Clinical Genetics
Friedreich Ataxia
Friedreich ataxia is an autosomal recessive neurodegenerative disorder, typically presenting in childhood or adolescence (usually before age 25), caused by GAA trinucleotide repeat expansions in the frataxin gene, leading to progressive gait and limb ataxia, dysarthria, loss of deep tendon reflexes, and hypertrophic cardiomyopathy.
Friedreich Ataxia (FRDA) — Paediatric-Focused Comprehensive Notes
Friedreich ataxia (FRDA) — from the Greek/Latin: "ataxia" = a- (without) + taxis (order), i.e., disordered movement — is an autosomal recessive (AR) progressive neurodegenerative disorder characterised by:
- Progressive spinocerebellar ataxia (both cerebellar and sensory components)
- Hypertrophic cardiomyopathy (leading cause of death)
- Skeletal deformities (scoliosis, pes cavus)
- Endocrinopathy (diabetes mellitus)
- Dysarthria and loss of deep tendon reflexes
It is caused by a GAA trinucleotide repeat expansion in the FXN gene on chromosome 9q21.11, leading to deficiency of the mitochondrial protein frataxin, resulting in mitochondrial iron accumulation and oxidative damage [1][2][3].
Key Definition — High Yield
Friedreich ataxia is the most common hereditary ataxia, caused by GAA trinucleotide repeat expansion in the FXN gene (chromosome 9q21), inherited in an autosomal recessive pattern, leading to frataxin deficiency, mitochondrial dysfunction, and progressive neurodegeneration with cardiomyopathy. [1][2]
2. Epidemiology
- Most common inherited ataxia worldwide
- Prevalence: approximately 1 in 50,000 in Caucasian populations
- Carrier frequency: approximately 1 in 100 in European populations
- Much rarer in East Asian populations, including Hong Kong Chinese — the prevalence is markedly lower compared to European populations. In Hong Kong and other East Asian settings, spinocerebellar ataxias (SCAs, autosomal dominant) are more common causes of hereditary ataxia than FRDA
- No sex predilection (autosomal recessive — affects males and females equally)
- Typical onset: 5–15 years of age (mean ~10–12 years)
- By definition, onset is almost always before age 25
- "Late-onset" FRDA (LOFA): onset between 25–50 years (milder phenotype, fewer GAA repeats)
- "Very late-onset" FRDA (VLOFA): onset > 50 years (uncommon)
- Important: this is predominantly a paediatric-onset disease, making it a key topic for paediatric neurology
- Progressive disability: most patients are wheelchair-bound within 10–15 years of symptom onset
- Mean age of death: ~35–40 years (range 20s–60s)
- Leading cause of death: cardiomyopathy (cardiac failure or arrhythmia) — accounts for ~60% of deaths
Hong Kong Context
FRDA is rare in the Hong Kong Chinese population compared to Caucasians. However, it remains examinable because it is the paradigmatic trinucleotide repeat disorder with AR inheritance and is a model for understanding mitochondrial iron metabolism. In Hong Kong, a child with progressive ataxia is more likely to have other hereditary ataxias (e.g., ataxia-telangiectasia) or acquired causes, but FRDA must be in the differential.
3. Anatomy and Function — Structures Affected
Understanding which structures are damaged in FRDA explains every clinical feature from first principles.
- Dorsal root ganglia (DRG): primary sensory neurones — the earliest and most severely affected structure
- DRG neurones are large cells with high metabolic demand → vulnerable to mitochondrial dysfunction
- Degeneration of DRG leads to → loss of proprioception and vibration sense (large fibre modalities carried by posterior columns)
- Posterior columns (fasciculus gracilis > cuneatus): carry proprioception, vibration, fine touch from DRG → medulla
- Degeneration → sensory ataxia (loss of position sense → cannot coordinate limbs without visual input)
- Spinocerebellar tracts (posterior > anterior): carry unconscious proprioception from peripheral receptors → cerebellum
- Degeneration → cerebellar ataxia component (cerebellum no longer receives afferent data about limb position)
- Corticospinal (pyramidal) tracts: lateral corticospinal tracts — upper motor neurone pathways
- Degeneration → extensor plantar responses (Babinski sign positive) and eventual spastic paraparesis
- This is why FRDA has an unusual combination: absent reflexes + upgoing plantars (see below)
- Dentate nucleus of cerebellum: the major output nucleus of the cerebellar hemisphere
- Degeneration → impaired motor planning, dysarthria, and limb coordination deficits
- Note: the cerebellar cortex itself is relatively spared (unlike spinocerebellar ataxias) — the damage is predominantly in deep nuclei and afferent tracts
- Myocardium: frataxin deficiency → mitochondrial iron overload in cardiomyocytes → hypertrophic cardiomyopathy (HCM)
- Later stages: dilated cardiomyopathy (as myocytes die and fibrosis supervenes)
- Cardiac conduction system involvement → arrhythmias
- Pancreatic β-cells: high metabolic demand, vulnerable to oxidative stress → diabetes mellitus (~10–30% of patients)
- Spinal column: progressive scoliosis due to paraspinal muscle weakness and imbalance
- Feet: pes cavus (high-arched foot) due to intrinsic foot muscle imbalance from denervation
- Optic atrophy may develop in some patients
4. Aetiology
High Yield — Trinucleotide Repeat Expansion
| Feature | Detail |
|---|---|
| Gene | FXN (frataxin gene) |
| Chromosome | 9q21.11 |
| Inheritance | Autosomal recessive (AR) [2][3] |
| Trinucleotide repeat | GAA [1][2] |
| Location of repeat | First intron (non-coding region of gene) |
| Normal repeat number | 5–33 GAA repeats |
| Premutation / borderline | 34–65 repeats |
| Full mutation (disease-causing) | > 66 repeats (typically 600–1200 repeats in most patients) |
| Mutation type in ~96% of cases | Homozygous GAA expansion (both alleles expanded) |
| Mutation type in ~4% of cases | Compound heterozygote: GAA expansion on one allele + point mutation/deletion on the other |
Key point from lecture slides: Examples of trinucleotide repeat expansion diseases include Fragile X syndrome (CGG), Friedreich ataxia (GAA), Myotonic dystrophy (CTG), Huntington disease (CAG), and Spinocerebellar ataxia (CAG). [1][2]
| Disease | Repeat | Gene | Inheritance | Coding/Non-coding | Key Mechanism |
|---|---|---|---|---|---|
| Friedreich ataxia | GAA | FXN | AR | Non-coding (intron 1) | ↓ Frataxin production |
| Fragile X syndrome | CGG | FMR1 | X-linked | Non-coding (5' UTR) | ↓ FMRP production |
| Huntington disease | CAG | HTT | AD | Coding | Toxic polyglutamine expansion |
| Myotonic dystrophy | CTG | DMPK | AD | Non-coding (3' UTR) | RNA toxic gain of function |
| Spinocerebellar ataxia | CAG | Various | AD | Coding | Toxic polyglutamine expansion |
Crucial Distinction — Coding vs Non-Coding Repeats
When the trinucleotide repeat is in a coding sequence, it produces a protein with excess amino acids (e.g., glutamine) → toxic polyglutamine expansion → neurodegeneration (e.g., Huntington disease). When the trinucleotide repeat is in a non-coding sequence, it decreases protein production (e.g., Friedreich ataxia → ↓ frataxin; Fragile X syndrome → ↓ FMRP). [1][2]
Students commonly confuse these mechanisms. FRDA does NOT produce a toxic protein — it produces too little normal protein.
Trinucleotide repeat disorders show anticipation: increasing severity and earlier age of onset in subsequent generations, because triplet repeats tend to expand during transmission. [1][2]
- In FRDA, anticipation is less prominent clinically compared to Huntington disease or myotonic dystrophy, because it is AR (requires both alleles to be affected)
- However, the underlying principle — that repeats are unstable and tend to expand during meiosis — still applies
- Larger GAA repeat size correlates with:
- Earlier age of onset
- More severe disease
- Higher risk of cardiomyopathy and diabetes
- Faster progression to wheelchair dependence
5. Pathophysiology — From Gene to Disease
This section explains the "why" behind every clinical feature. Understanding this chain lets you derive the entire clinical picture from first principles.
- The GAA expansion in intron 1 causes the DNA to form an abnormal triple-helical structure (R-loop / sticky DNA)
- This structure physically blocks RNA polymerase during transcription → gene silencing
- Also promotes heterochromatin formation (epigenetic silencing via histone deacetylation and DNA methylation)
- Result: markedly reduced (not absent) frataxin protein levels — typically 5–30% of normal
- Carriers (heterozygous) have ~50% frataxin — clinically unaffected
- Patients (homozygous) have 5–30% frataxin — clinically affected
- Complete absence of frataxin is embryonically lethal
-
Frataxin is a small mitochondrial protein (210 amino acids) that functions in:
- Iron-sulphur (Fe-S) cluster biogenesis — essential cofactors for mitochondrial respiratory chain complexes (Complexes I, II, III) and aconitase
- Iron homeostasis within mitochondria — acts as an iron chaperone, preventing free iron accumulation
- Heme biosynthesis — last step occurs in mitochondria and requires iron delivery
-
When frataxin is deficient:
- Iron accumulates in mitochondria as free (non-sequestered) iron
- Fe-S cluster assembly is impaired → dysfunctional respiratory chain complexes
- Cytoplasmic iron is depleted → upregulation of cellular iron uptake → even more iron floods into mitochondria (vicious cycle)
- Free mitochondrial iron participates in Fenton reactions:
- Fe²⁺ + H₂O₂ → Fe³⁺ + OH⁻ + OH• (hydroxyl radical — extremely damaging)
- This generates massive reactive oxygen species (ROS)
- ROS damage:
- Mitochondrial DNA (which lacks protective histones and has limited repair capacity)
- Mitochondrial membranes (lipid peroxidation)
- Respiratory chain enzymes (further ↓ ATP production)
- Combined effect: impaired ATP production + oxidative damage → cell death
Why certain tissues? The key is metabolic demand and dependence on oxidative phosphorylation:
| Tissue | Why Vulnerable? | Clinical Consequence |
|---|---|---|
| Dorsal root ganglia | Large neurones, high metabolic rate, long axons | Sensory ataxia, areflexia |
| Posterior columns | Dependent on DRG neuronal health | Loss of proprioception/vibration |
| Spinocerebellar tracts | Long axons, high energy demand | Cerebellar ataxia |
| Corticospinal tracts | Long upper motor neurones | Upgoing plantars, eventual spasticity |
| Dentate nucleus | Major cerebellar output, high firing rate | Dysarthria, intention tremor |
| Cardiomyocytes | Constantly contracting, entirely dependent on mitochondrial oxidative phosphorylation | Hypertrophic cardiomyopathy |
| Pancreatic β-cells | Metabolically active, sensitive to oxidative stress | Diabetes mellitus |
6. Classification
| Subtype | Age of Onset | GAA Repeat Size | Clinical Features |
|---|---|---|---|
| Classic / Typical FRDA | < 25 years (usually 5–15 years) | Large (typically 600–1200) | Full phenotype: ataxia, cardiomyopathy, scoliosis, diabetes |
| Late-Onset FRDA (LOFA) | 25–50 years | Smaller (typically < 500 on at least one allele) | Slower progression, milder cardiomyopathy, reflexes may be retained |
| Very Late-Onset FRDA (VLOFA) | > 50 years | Smallest expansions | Mildest phenotype |
| Genotype | Frequency | Features |
|---|---|---|
| Homozygous GAA expansion | ~96% | Typical FRDA phenotype |
| Compound heterozygote (GAA expansion + point mutation/deletion) | ~4% | May have atypical features depending on the nature of the second mutation |
- FRDA with retained reflexes (FARR): a subset of patients with smaller expansions who retain knee/ankle jerks — contradicts the "classic" teaching of universal areflexia
- Acadian FRDA: described in the Acadian population of Louisiana — slower progression despite typical repeat sizes
7. Clinical Features
- Typical presentation: a child aged 5–15 years presenting with progressive gait unsteadiness and frequent falls
- Initially may be mistaken for "clumsiness" or dismissed
- The progressive nature and combination of neurological + cardiac + skeletal findings should raise suspicion
- Family history may reveal consanguinity or affected siblings (AR inheritance)
7.2 Symptoms — With Pathophysiological Basis
| Symptom | Pathophysiological Basis |
|---|---|
| Progressive gait ataxia (earliest and most consistent symptom) | Combined sensory ataxia (posterior column degeneration → loss of proprioception) AND cerebellar ataxia (spinocerebellar tract + dentate nucleus degeneration). The child cannot sense where their limbs are AND cannot coordinate motor output. |
| Limb ataxia (clumsiness, difficulty with fine motor tasks, poor handwriting) | Cerebellar hemisphere dysfunction (dentate nucleus degeneration) → impaired motor planning + loss of proprioceptive feedback from spinocerebellar tract degeneration |
| Dysarthria (slow, slurred, scanning speech — described as "cerebellar speech") | Dentate nucleus degeneration → impaired coordination of muscles of speech production. Scanning dysarthria = each syllable given equal emphasis, losing normal speech prosody |
| Dysphagia (difficulty swallowing, especially in later stages) | Progressive bulbar dysfunction from brainstem involvement + cerebellar dysfunction affecting swallowing coordination |
| Fatigue / exercise intolerance | Mitochondrial dysfunction → impaired ATP production in skeletal muscle |
| Loss of balance, frequent falls | Combined proprioceptive loss + cerebellar dysfunction → inability to maintain balance, especially with eyes closed or on uneven surfaces |
| Visual symptoms (blurred vision, later stages) | Optic atrophy from degeneration of optic nerve fibres (some patients) |
| Hearing impairment (some patients) | Auditory nerve / cochlear neurone involvement |
| Symptom | Pathophysiological Basis |
|---|---|
| Dyspnoea on exertion | Hypertrophic cardiomyopathy → diastolic dysfunction → ↓ cardiac output on exercise |
| Palpitations | Cardiac conduction system involvement → arrhythmias (especially atrial fibrillation) |
| Chest pain | Myocardial ischaemia from hypertrophied myocardium outgrowing its blood supply |
| Syncope / presyncope | Arrhythmias or outflow obstruction in severe HCM |
| Symptoms of heart failure (oedema, orthopnoea — late) | Progression from HCM to dilated cardiomyopathy → systolic failure |
Cardiac involvement is often asymptomatic in childhood but is the leading cause of death. Regular echocardiographic screening is essential.
| Symptom | Pathophysiological Basis |
|---|---|
| Polyuria, polydipsia, weight loss | Diabetes mellitus from pancreatic β-cell oxidative damage → insulin deficiency / insulin resistance. Can be insulin-dependent or non-insulin-dependent |
| Symptom | Pathophysiological Basis |
|---|---|
| Back pain / deformity | Progressive scoliosis from paraspinal muscle weakness + imbalanced innervation |
| Foot deformity | Pes cavus → discomfort with footwear, abnormal gait biomechanics |
7.3 Signs — With Pathophysiological Basis
This is the most clinically important section. FRDA has a unique and characteristic combination of signs that is highly testable.
The FRDA Triad — Must Know for Exams
Friedreich ataxia is characterised by the unusual combination of:
- Absent deep tendon reflexes (areflexia) — from dorsal root ganglion / peripheral sensory neurone degeneration
- Extensor plantar responses (upgoing plantars / Babinski positive) — from corticospinal tract degeneration
- Progressive ataxia — from combined sensory and cerebellar pathways
This combination of areflexia + upgoing plantars is almost unique to FRDA and should trigger this diagnosis immediately in a paediatric patient with progressive ataxia.
Why is this combination unusual?
- Normally, absent reflexes suggest a lower motor neurone (LMN) lesion (e.g., peripheral neuropathy)
- Normally, upgoing plantars suggest an upper motor neurone (UMN) lesion (e.g., corticospinal tract disease)
- Having both simultaneously means there is concurrent LMN-type sensory neurone loss (DRG degeneration) AND UMN corticospinal tract degeneration — exactly what happens in FRDA
| Sign | Finding | Pathophysiological Basis |
|---|---|---|
| Gait ataxia | Wide-based, lurching, unsteady gait | Combined sensory + cerebellar ataxia |
| Romberg sign | Positive (worsens with eyes closed) | Proprioceptive (sensory) ataxia component — the patient is relying on vision to compensate for lost proprioception; removing vision → falls. This distinguishes the sensory component. Pure cerebellar ataxia = Romberg negative |
| Areflexia | Absent knee and ankle jerks (may be generalised) | DRG degeneration → loss of Ia afferent fibres that form the afferent limb of the monosynaptic stretch reflex arc |
| Extensor plantars (Babinski +) | Upgoing great toe on plantar stimulation | Corticospinal (pyramidal) tract degeneration → loss of UMN inhibition of the primitive extension reflex |
| Limb ataxia | Dysmetria (finger-nose and heel-shin test overshooting), intention tremor, dysdiadochokinesia | Spinocerebellar tract + dentate nucleus degeneration |
| Dysarthria | Scanning / cerebellar speech: slow, slurred, equal emphasis on each syllable | Cerebellar dysfunction affecting coordination of speech muscles |
| Loss of proprioception | Impaired joint position sense (tested at great toe, ankle, fingers) | Posterior column degeneration (fasciculus gracilis) |
| Loss of vibration sense | Impaired vibration perception (tuning fork, 128 Hz) | Posterior column degeneration |
| Nystagmus | May be present (horizontal or gaze-evoked) | Cerebellar / vestibular pathway involvement |
| Optic atrophy | Pale optic disc on fundoscopy | Optic nerve fibre degeneration |
| Sensorineural hearing loss | Audiometric abnormality (some patients) | Auditory nerve degeneration |
| Weakness (later stages) | Distal > proximal muscle weakness, especially lower limbs | Corticospinal tract degeneration (UMN) + possibly some anterior horn cell involvement |
| Spasticity (very late) | Increased tone in lower limbs | Corticospinal tract degeneration (becomes apparent as disease progresses and UMN signs dominate) |
Note: The cerebellar signs in FRDA are due to spinocerebellar tract and dentate nucleus degeneration, NOT primarily cerebellar cortical degeneration. The cerebellum itself is relatively preserved on imaging. [3][4]
| Sign | Finding | Pathophysiological Basis |
|---|---|---|
| Pes cavus | High-arched foot with hammer toes | Imbalance between intrinsic and extrinsic foot muscles due to denervation → the long extensors and flexors (extrinsic, still relatively preserved) overpower the weak intrinsic muscles → arch elevation and toe clawing |
| Scoliosis | Progressive kyphoscoliosis | Paraspinal muscle weakness + imbalanced neural input → asymmetric spinal forces → curvature. Can be severe enough to require surgical correction and may compromise respiratory function |
| Muscle wasting (late) | Distal wasting, especially in hands and feet | Combined neuropathic (DRG loss) and disuse atrophy |
| Sign | Finding | Pathophysiological Basis |
|---|---|---|
| Systolic murmur | Flow murmur or LVOT obstruction murmur | Hypertrophic cardiomyopathy — especially if asymmetric septal hypertrophy causes dynamic left ventricular outflow tract (LVOT) obstruction |
| S4 gallop | Presystolic sound | Stiff, hypertrophied ventricle → atrial contraction against non-compliant ventricle |
| Displaced apex beat | Laterally displaced (if cardiomegaly develops) | Progression to dilated cardiomyopathy |
| Signs of heart failure (late) | Elevated JVP, bibasal crackles, peripheral oedema | End-stage dilated cardiomyopathy with systolic failure |
| Irregular pulse | Irregularly irregular or tachycardia | Atrial fibrillation or other arrhythmias |
| Sign | Finding | Pathophysiological Basis |
|---|---|---|
| Diabetes mellitus | Glycosuria, hyperglycaemia | β-cell dysfunction from oxidative stress + possible insulin resistance |
| Short stature (sometimes) | Below expected height for age | Chronic disease, possibly scoliosis contribution |
| System | Features |
|---|---|
| Neurological | Progressive gait + limb ataxia (sensory + cerebellar), areflexia, extensor plantars, dysarthria, posterior column sensory loss (proprioception, vibration), nystagmus, optic atrophy, sensorineural hearing loss |
| Cardiac | Hypertrophic cardiomyopathy → dilated cardiomyopathy, arrhythmias, heart failure |
| Musculoskeletal | Pes cavus, scoliosis (kyphoscoliosis), foot deformity |
| Endocrine | Diabetes mellitus (~10–30%) |
| Other | Fatigue, dysphagia (late), bladder dysfunction (late) |
- Progressive ataxia beginning in childhood/adolescence (age 5–15)
- Areflexia with upgoing plantars — this combination is near-pathognomonic
- Pes cavus — especially bilateral in a child with gait difficulties
- Scoliosis — especially progressive, in combination with neurological signs
- Family history of ataxia, cardiomyopathy, or consanguinity (AR pattern)
- Cardiac murmur or ECG abnormalities in a child with ataxia
Clinical Pearl
In any child with progressive ataxia, always examine the feet for pes cavus, the spine for scoliosis, check reflexes carefully (looking for the areflexia + upgoing plantar combination), and listen to the heart. If you find this constellation → think Friedreich ataxia first.
| Feature | Friedreich Ataxia | Ataxia-Telangiectasia | Spinocerebellar Ataxia (SCA) |
|---|---|---|---|
| Inheritance | AR | AR | AD |
| Onset | Childhood (5–15 years) | Infancy/early childhood (1–4 years) | Usually adulthood |
| Reflexes | Absent | Variable | Usually brisk (UMN pattern) |
| Plantars | Extensor | Variable | Usually extensor |
| Cardiomyopathy | Yes (hallmark) | No | Variable by type |
| Pes cavus | Yes | Usually no | Variable |
| Telangiectasia | No | Yes (conjunctival + skin) | No |
| Immunodeficiency | No | Yes (recurrent sinopulmonary infections) | No |
| AFP | Normal | Elevated | Normal |
| Malignancy risk | Not increased | Increased (lymphoma, leukaemia) | Not typically |
8. Age-Specific Considerations in Paediatrics
- Progressive ataxia significantly impacts motor development milestones — initially the child may have achieved normal milestones, but regression or plateau is noted
- Cognitive function is typically preserved — this is an important distinction from many other neurodegenerative disorders. The child is intellectually intact but physically disabled
- Psychosocial impact is enormous: a previously active child who played sport becomes wheelchair-bound → depression, anxiety, school difficulties, social isolation → family-centred care and psychological support are essential
- The child (especially adolescents) should be involved in discussions about their condition (assent)
- Genetic counselling for the family is critical — AR inheritance means:
- Each sibling has a 25% chance of being affected
- Each sibling has a 50% chance of being a carrier
- Carrier testing and prenatal diagnosis are available
- As FRDA patients survive into adulthood, transition from paediatric to adult services is an important consideration
- Involves coordination between paediatric neurology, cardiology, endocrinology, orthopaedics, physiotherapy, occupational therapy, speech therapy, and psychological services
When assessing a child with suspected FRDA, know these reference points:
| Parameter | Normal for Age | Relevance |
|---|---|---|
| Deep tendon reflexes | Present (1+ to 3+) by age 1 year | Absent in FRDA |
| Plantar response | Flexor (downgoing) from ~12–18 months onwards | Extensor in FRDA (note: up to 12 months, upgoing plantars can be normal) |
| Gait | Independent walking by 12–18 months; mature gait pattern by 7–8 years | Progressive deterioration in FRDA |
| Fasting glucose | 3.3–5.6 mmol/L (children) | May be elevated in FRDA |
| HbA1c | < 5.7% (< 39 mmol/mol) | May be elevated |
| Echocardiographic LV wall thickness | Age-dependent (z-scores used); > +2 SD = hypertrophy | HCM in FRDA |
High Yield Summary
Friedreich Ataxia — Key Points for Exams:
- Most common hereditary ataxia; autosomal recessive inheritance
- GAA trinucleotide repeat expansion in intron 1 (non-coding) of FXN gene (chromosome 9q21) → ↓ frataxin
- Non-coding repeat → decreased protein production (not toxic protein accumulation)
- Frataxin deficiency → impaired Fe-S cluster assembly → mitochondrial iron accumulation → oxidative stress → cell death
- Onset typically age 5–15 years with progressive gait ataxia
- Pathognomonic sign combination: areflexia + extensor plantars (upgoing Babinski) — concurrent LMN (DRG) + UMN (corticospinal) degeneration
- Key affected structures: dorsal root ganglia, posterior columns, spinocerebellar tracts, corticospinal tracts, dentate nucleus, cardiomyocytes, pancreatic β-cells
- Cardinal features: progressive ataxia (sensory + cerebellar), dysarthria, pes cavus, scoliosis, hypertrophic cardiomyopathy, diabetes mellitus
- Leading cause of death: cardiomyopathy (cardiac failure/arrhythmia)
- Larger GAA repeat size → earlier onset, more severe disease (anticipation principle)
- Cognition typically preserved — distinguish from other neurodegenerative disorders
- Listed alongside Fragile X syndrome (CGG), Myotonic dystrophy (CTG), Huntington disease (CAG), and Spinocerebellar ataxia (CAG) as key trinucleotide repeat disorders
Active Recall — Friedreich Ataxia (Definition to Clinical Features)
[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p497 — Trinucleotide repeat expansion mutation section) [2] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p881 — Genetics of Fragile X syndrome / Triplet expansion disorders) [3] Senior notes: Ryan Ho Neurology.pdf (p117 — Approach to Cerebellar Syndrome, Aetiology table: Hereditary — Friedreich's ataxia (AR)) [4] Senior notes: Ryan Ho Fundamentals.pdf (p333 — Cerebellar Syndrome, D/dx of cerebellar ataxia)
Friedreich Ataxia — Differential Diagnosis
1. Approach to the Differential Diagnosis
Before jumping into the list, let's think about this from first principles. A child (typically 5–15 years old) walks into your clinic with progressive gait unsteadiness. Your job is to localise the lesion, then work through the aetiologies systematically.
The core presentation of Friedreich ataxia is:
- Progressive ataxia (combined sensory + cerebellar)
- Areflexia with extensor plantars (mixed LMN + UMN pattern)
- Pes cavus and scoliosis (skeletal deformities)
- Cardiomyopathy (hypertrophic)
- Onset in childhood/adolescence
Therefore, the differential diagnosis must address:
- Other causes of progressive ataxia in childhood (the primary differential)
- Conditions that mimic the mixed LMN/UMN pattern (areflexia + upgoing plantars)
- Other causes of childhood hypertrophic cardiomyopathy with neurological features
From GC lecture slides: The approach to any neurological presentation should systematically ask "Where is the lesion?" (anatomical localisation) then "What is the lesion?" (pathological differentials), using the mnemonic: Vascular, Infection, Neoplasm, Degenerative, Inflammatory, Congenital, Autoimmune, Trauma/Toxins, Endocrine [5][6]
Where is the lesion? [5][6] In FRDA, multiple sites are involved simultaneously:
- Posterior columns (sensory ataxia)
- Spinocerebellar tracts (cerebellar ataxia)
- Corticospinal tracts (UMN signs)
- Dorsal root ganglia (areflexia, sensory loss)
- Dentate nucleus of cerebellum
The differential must therefore include any condition that can affect multiple levels of the neuraxis — the spinal cord, cerebellum, peripheral nerves, and/or dorsal root ganglia.
Physical examination should assess: distribution and character of weakness (unilateral/bilateral, proximal/distal, UMN/LMN pattern), sensory impairment (proprioception, vibration, dermatomal/sensory level), cranial nerve and cerebellar signs, and sphincter disturbances. [7]
2. Differential Diagnosis — Structured by Category
2.2 Hereditary Ataxias (The Core Differential)
These are the conditions most commonly confused with FRDA. The table below is high-yield.
| Feature | Detail |
|---|---|
| Inheritance | Autosomal recessive (AR) — like FRDA |
| Gene / Protein | ATM gene (chromosome 11q22) → ATM kinase (DNA damage response) |
| Age of onset | Earlier than FRDA: typically 1–4 years (toddler stage) |
| Ataxia type | Primarily cerebellar (truncal > limb) — progressive |
| Key distinguishing features | Oculocutaneous telangiectasias (conjunctival blood vessels + ears/antecubital fossa — appear age 3–6 years), immunodeficiency (recurrent sinopulmonary infections from IgA and IgG subclass deficiency), elevated serum AFP, increased cancer risk (lymphoma, leukaemia) |
| Reflexes | Variable (may be reduced but not characteristically absent) |
| Cardiomyopathy | No |
| Why it's different from FRDA | Telangiectasias, immunodeficiency, and elevated AFP are NOT seen in FRDA. A-T onset is earlier. No cardiomyopathy in A-T |
High Yield — A-T vs FRDA
Both are AR childhood-onset progressive ataxias. The key discriminators are: A-T has telangiectasias + immunodeficiency + ↑AFP + cancer risk while FRDA has cardiomyopathy + diabetes + pes cavus + areflexia with upgoing plantars.
| Feature | Detail |
|---|---|
| Inheritance | Autosomal dominant (AD) — fundamentally different from FRDA (AR) [3][4] |
| Trinucleotide repeat | CAG repeat expansions (most types) — coding region → toxic polyglutamine protein [1][2] |
| Age of onset | Typically adulthood (20s–50s), though juvenile-onset forms exist |
| Ataxia type | Primarily cerebellar (gait + limb ataxia, dysarthria, nystagmus) |
| Reflexes | Usually brisk (hyperreflexia) — UMN predominant pattern (contrast with FRDA's areflexia) |
| Key distinguishing features | AD family history (affected parent), adult onset, brisk reflexes, NO cardiomyopathy, NO pes cavus typically |
| Hong Kong relevance | More common than FRDA in East Asian populations — SCA3 (Machado-Joseph disease) is the most common SCA subtype globally and in Chinese populations |
From lecture slides: Hereditary causes of chronic progressive bilateral cerebellar ataxia include Spinocerebellar ataxia (AD), Friedreich's ataxia (AR), Ataxia-telangiectasia (AR), Wilson's disease (AR), and Mitochondrial diseases. [3][4]
| Feature | Detail |
|---|---|
| Inheritance | AR |
| Gene | TTPA (α-tocopherol transfer protein) on chromosome 8q |
| Why important | Clinical phenocopy of FRDA — progressive ataxia, areflexia, pes cavus, cardiomyopathy, scoliosis |
| Key distinguishing feature | Very low serum vitamin E levels — FRDA has normal vitamin E |
| Why it matters clinically | Treatable! Vitamin E supplementation halts or reverses progression |
Don't Miss This
Ataxia with Vitamin E Deficiency (AVED) is a clinical mimic of FRDA that is treatable. Always check serum vitamin E levels in any child with an FRDA-like phenotype. Missing this diagnosis means missing a chance to halt disease progression with simple vitamin E supplementation.
| Feature | Detail |
|---|---|
| Inheritance | AR |
| Gene | SACS (sacsin) |
| Clinical features | Early-onset cerebellar ataxia + spasticity + peripheral neuropathy |
| Key distinguishing features | Prominent spasticity (unlike FRDA where spasticity is late); retinal nerve fibre layer thickening on OCT; less prominent cardiomyopathy |
| Feature | Detail |
|---|---|
| Inheritance | AR |
| Defect | Phytanic acid oxidase deficiency → phytanic acid accumulation |
| Clinical features | Cerebellar ataxia, peripheral neuropathy (areflexia), retinitis pigmentosa, ichthyosis, cardiomyopathy |
| Key distinguishing features | Retinitis pigmentosa and ichthyosis (dry, scaly skin) — not seen in FRDA. Elevated serum phytanic acid diagnostic. Treatable with dietary restriction of phytanic acid |
2.3 Non-Hereditary Ataxias in the Differential (Paediatric)
These must be considered and excluded, especially when the presentation is not classical.
| Feature | Detail |
|---|---|
| Tempo | Acute onset (hours to days) — unlike FRDA's insidious progressive course |
| Age | Typically 2–6 years |
| Cause | Post-viral immune-mediated cerebellar inflammation (varicella, EBV, enterovirus) |
| Course | Self-limiting — resolves completely within weeks to months |
| Why different from FRDA | Acute onset, non-progressive, no skeletal deformities, no cardiomyopathy, no sensory loss, reflexes preserved |
| Feature | Detail |
|---|---|
| Types | Medulloblastoma, ependymoma, cerebellar astrocytoma (pilocytic) [8] |
| Tempo | Subacute to chronic progressive (weeks to months) |
| Key features | Raised intracranial pressure (headache worse in morning, vomiting, papilloedema), cranial nerve palsies, hydrocephalus |
| Why different from FRDA | Signs of raised ICP, often unilateral cerebellar signs, no sensory loss, no areflexia, no cardiomyopathy. MRI brain diagnostic |
From lecture slides: Brain tumours must be considered in any child with progressive neurological symptoms. Mass in the brain — think brain tumours. [8]
| Feature | Detail |
|---|---|
| Tempo | Relapsing-remitting (MS) or acute monophasic (ADEM) |
| Age | Paediatric MS uncommon but occurs; ADEM more common in young children |
| Key features | Relapsing course with dissemination in time and space (MS); optic neuritis, transverse myelitis. ADEM: post-infectious, encephalopathy, multifocal white matter lesions |
| Why different from FRDA | Relapsing course, MRI white matter lesions, CSF oligoclonal bands (MS), NO pes cavus or cardiomyopathy |
The signature finding in FRDA is areflexia + upgoing plantars. Other conditions with this mixed pattern:
| Condition | Mechanism | Distinguishing Features |
|---|---|---|
| Subacute combined degeneration (Vitamin B12 deficiency) | Posterior column + corticospinal tract degeneration + peripheral neuropathy | Adults typically; macrocytic anaemia; low serum B12; responds to B12 replacement. Rare in paediatrics but can occur with strict vegan diets or inborn errors of B12 metabolism |
| Adrenomyeloneuropathy (X-linked) | Spinal cord (corticospinal + posterior column) + peripheral neuropathy | Males; elevated very long chain fatty acids (VLCFA); adrenal insufficiency; progressive spastic paraparesis |
| Motor neurone disease (ALS) | Combined UMN + LMN degeneration | Adults (not paediatric); NO sensory loss; fasciculations; rapidly progressive. Included for completeness but NOT a paediatric differential [9] |
| Tabes dorsalis (neurosyphilis) | Posterior column + dorsal root degeneration | Extremely rare in paediatrics; historical interest; Argyll Robertson pupils |
| Feature | Detail |
|---|---|
| Inheritance | AR [3][4] |
| Gene | ATP7B (chromosome 13q14) |
| Pathophysiology | Defective copper excretion → copper accumulation in liver, brain (basal ganglia, cerebellum), cornea |
| Neurological features | Ataxia, dystonia, tremor, dysarthria, parkinsonism [10] |
| Key distinguishing features | Kayser-Fleischer rings (corneal copper deposits), liver disease (acute hepatitis, chronic hepatitis, cirrhosis, fulminant liver failure with Coombs-negative haemolytic anaemia), low serum caeruloplasmin, elevated 24-hour urine copper |
| Why crucial | Treatable! Copper chelation (penicillamine, trientine) and zinc supplementation can prevent progression |
| Paediatric onset | Liver disease typically presents first in children (5–15 years); neurological features more common in adolescents/young adults |
From senior notes: Wilson disease can mimic Parkinsonism (extrapyramidal deposition of copper). Penicillamine causes worsened neurological symptoms initially. Fulminant hepatic failure from Wilson disease presents with Coombs-negative haemolytic anaemia. [10]
Two Treatable Mimics — Must Not Miss
In any child with progressive ataxia, you MUST exclude:
- Vitamin E deficiency (AVED) — check serum vitamin E
- Wilson disease — check slit-lamp for KF rings, serum caeruloplasmin, 24-hour urine copper
Both are treatable AR conditions that can mimic FRDA. Missing them is clinically catastrophic.
2.6 Other Conditions in the Paediatric Differential
| Feature | Detail |
|---|---|
| Inheritance | AD (most common, CMT1A), AR, or X-linked |
| Core problem | Peripheral nerve demyelination or axonal degeneration |
| Shared features with FRDA | Pes cavus, hammer toes, areflexia, distal weakness, scoliosis |
| Key differences | No cerebellar ataxia (pure peripheral neuropathy → sensory ataxia possible but no dysarthria/nystagmus/intention tremor), no cardiomyopathy, no upgoing plantars (LMN pattern only — downgoing plantars). Nerve conduction studies show demyelinating or axonal neuropathy |
| Feature | Detail |
|---|---|
| Inheritance | AR; caused by SMN1 gene deletion on chromosome 5q13 [11] |
| Core problem | Progressive degeneration of anterior horn cells → pure LMN disease [11] |
| Key differences | Motor-only (no sensory involvement), proximal weakness predominant, tongue fasciculations, NO ataxia, NO upgoing plantars, NO cardiomyopathy, NO pes cavus |
SMA = anterior horn cell degeneration → hypotonia, generalized weakness, areflexia. Unlike FRDA, SMA is pure motor (no sensory or cerebellar involvement). [11]
| Feature | Detail |
|---|---|
| Nature | Non-progressive motor disorder due to prenatal/perinatal brain injury [12] |
| Why considered | The ataxic subtype of CP can present with gait ataxia and coordination difficulties |
| Key differences | Non-progressive (FRDA is progressive), onset from birth/early infancy (not age 5–15), no cardiomyopathy, no sensory loss, often associated with intellectual disability (FRDA preserves cognition) |
CP remains a clinical diagnosis. Specific CP subtypes are best recognised after 5 years of age. Ataxia may not be apparent even later. [12]
| Feature | Detail |
|---|---|
| Inheritance | Maternal (mitochondrial) or AR/AD (nuclear-encoded mitochondrial genes) |
| Examples | MELAS, MERRF, Kearns-Sayre syndrome, Leigh disease |
| Shared features | Ataxia, cardiomyopathy, diabetes — all overlap with FRDA |
| Key differences | Multi-system features (stroke-like episodes, seizures, myoclonus, ophthalmoplegia, lactic acidosis, ragged red fibres on muscle biopsy), maternal inheritance pattern in many cases. MRI often shows basal ganglia or white matter abnormalities (not typical of FRDA) |
Mitochondrial diseases are listed as a cause of hereditary chronic progressive bilateral cerebellar ataxia. [3][4]
| Feature | Detail |
|---|---|
| Inheritance | AR |
| Core problem | Lysosomal storage disorder → accumulation of ceroid lipofuscin in neurones |
| Clinical features | Progressive ataxia, seizures, myoclonus, visual loss (retinal degeneration), cognitive decline |
| Key differences | Seizures and visual loss are prominent (not typical of FRDA); cognitive decline (FRDA preserves cognition). Electron microscopy shows characteristic inclusions |
| Feature | Detail |
|---|---|
| Inheritance | AR |
| Core problem | Inability to synthesise apolipoprotein B → fat malabsorption → secondary vitamin E deficiency |
| Clinical features | Progressive ataxia, areflexia, retinitis pigmentosa, acanthocytosis (spiky RBCs on blood film) |
| Key differences | Acanthocytes on peripheral blood smear, fat malabsorption (steatorrhoea), very low serum cholesterol and triglycerides, retinitis pigmentosa. Like AVED, responds to vitamin E supplementation |
| Condition | Inheritance | Key Discriminating Features vs FRDA |
|---|---|---|
| Ataxia-telangiectasia | AR | Earlier onset (1–4y), telangiectasias, immunodeficiency, ↑AFP, cancer risk, NO cardiomyopathy |
| Spinocerebellar ataxias | AD | Adult onset, brisk reflexes, AD family history, NO cardiomyopathy, NO pes cavus |
| AVED (Vitamin E deficiency) | AR | Phenocopy of FRDA — distinguish by low vitamin E. Treatable! |
| Wilson disease | AR | KF rings, liver disease, dystonia/tremor, low caeruloplasmin, ↑urine copper. Treatable! |
| CMT (HMSN) | AD/AR/XL | Pure peripheral neuropathy, NO cerebellar signs, NO cardiomyopathy, NO upgoing plantars |
| SMA | AR | Pure motor (anterior horn cells), NO sensory or cerebellar involvement |
| Cerebral palsy (ataxic) | N/A | Non-progressive, onset from birth |
| Mitochondrial disorders | Maternal/AR/AD | Multi-system (stroke-like episodes, seizures, lactic acidosis), maternal inheritance |
| Posterior fossa tumour | N/A | Raised ICP, unilateral signs, MRI abnormal |
| Acute cerebellar ataxia | N/A | Acute onset, self-limiting, post-viral |
| Refsum disease | AR | Retinitis pigmentosa, ichthyosis, ↑phytanic acid. Treatable! |
| Abetalipoproteinaemia | AR | Acanthocytes, fat malabsorption, retinitis pigmentosa. Treatable! |
5. Key Principles for the Paediatric Differential
In any child with progressive ataxia, the priority is to identify treatable conditions before settling on an untreatable diagnosis like FRDA:
| Treatable Mimic | Screening Test | Treatment |
|---|---|---|
| AVED | Serum vitamin E | Vitamin E supplementation |
| Wilson disease | Caeruloplasmin, 24h urine copper, slit-lamp exam | Copper chelation (penicillamine/trientine) + zinc |
| Refsum disease | Serum phytanic acid | Dietary restriction of phytanic acid, plasmapheresis |
| Abetalipoproteinaemia | Fasting lipid panel, peripheral blood film (acanthocytes) | Fat-soluble vitamin supplementation (especially vitamin E) |
| B12 deficiency | Serum B12, methylmalonic acid | B12 supplementation |
| Posterior fossa tumour | MRI brain with contrast | Surgery ± chemotherapy ± radiotherapy |
| Hypothyroidism | TFT | Thyroxine replacement |
If any of the following are present, reconsider the diagnosis:
- Cognitive decline or intellectual disability → think metabolic/storage disorders, NCL, mitochondrial
- Seizures → think NCL, mitochondrial, metabolic
- Ophthalmoplegia → think mitochondrial (Kearns-Sayre), SCA
- Skin findings (telangiectasia, ichthyosis) → think A-T, Refsum
- Hepatosplenomegaly or liver disease → think Wilson, metabolic/storage
- Brisk reflexes throughout → think SCA, HSP (not FRDA)
- Non-progressive course → think CP
- Acute onset → think post-infectious, tumour, stroke
| Age Group | More Likely Differentials |
|---|---|
| Infant / Toddler (0–3 years) | Ataxic CP, ataxia-telangiectasia (onset 1–4y), SMA, metabolic/storage disorders |
| Early childhood (3–8 years) | Acute cerebellar ataxia (post-viral), posterior fossa tumour, A-T, early FRDA |
| Late childhood / Adolescence (8–18 years) | FRDA (classic onset), Wilson disease, AVED, CMT, SCA (juvenile forms), mitochondrial |
High Yield Summary — Differential Diagnosis of Friedreich Ataxia
- FRDA is the most common hereditary ataxia — but always exclude treatable mimics first (AVED, Wilson, Refsum, abetalipoproteinaemia, B12 deficiency, tumour)
- The pathognomonic triad (areflexia + upgoing plantars + progressive ataxia) distinguishes FRDA from most differentials
- Ataxia-telangiectasia is the main AR childhood ataxia differential — distinguished by telangiectasias, immunodeficiency, ↑AFP, cancer risk
- Spinocerebellar ataxias (AD) are more common than FRDA in East Asian / Hong Kong Chinese populations — adult onset, brisk reflexes, AD inheritance
- AVED is a clinical phenocopy of FRDA that is treatable with vitamin E — always check serum vitamin E
- Wilson disease must be excluded in any child with progressive ataxia — slit-lamp exam, caeruloplasmin, urine copper
- SMA (AR, motor-only) and CMT (peripheral neuropathy only) lack cerebellar and sensory features of FRDA
- Non-progressive ataxia → think cerebral palsy; acute onset → think post-infectious or tumour
Active Recall — Differential Diagnosis of Friedreich Ataxia
[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p497 — Trinucleotide repeat expansion mutation section) [2] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p881 — Genetics of Fragile X syndrome / Triplet expansion disorders) [3] Senior notes: Ryan Ho Neurology.pdf (p117 — Approach to Cerebellar Syndrome, Aetiology table) [4] Senior notes: Ryan Ho Fundamentals.pdf (p333 — Cerebellar Syndrome, D/dx of cerebellar ataxia) [5] Lecture slides: CFB_Neuro clinical skills demonstration_01.08.22_file to students.pdf (p7 — Where is the lesion; p8 — What is the lesion) [6] Lecture slides: GC 094. Where is the lesion I.pdf [7] Lecture slides: Neurology- Two cases of lower limb weakness.pdf (p20 — Physical Examination and localisation) [8] Lecture slides: GC 108. A mass in the brain brain tumours.pdf [9] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p1289 — ALS diagnostic criteria) [10] Senior notes: Ryan Ho GI.pdf (p297 — Wilson disease clinical features) [11] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p535-538 — Spinal muscular atrophy) [12] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p464 — Differential diagnosis and diagnosis of CP)
Friedreich Ataxia — Diagnostic Criteria, Diagnostic Algorithm & Investigations
1. Diagnostic Criteria
Unlike many conditions (e.g., rheumatic fever with Jones criteria, or SLE with SLICC criteria), Friedreich ataxia does not have a universally adopted clinical diagnostic criteria set published by an international body. This is because:
- Genetic testing is definitive — since 1996, when the FXN gene and GAA expansion were identified, diagnosis has shifted from clinical criteria to molecular confirmation
- Historical clinical criteria (e.g., Harding 1981, Geoffroy 1976) were used before the genetic era and remain useful for clinical suspicion — telling you when to order the genetic test
These criteria were developed by Professor Anita Harding and remain the most widely cited clinical diagnostic framework. They define who should be suspected of having FRDA based on clinical features alone.
Harding Essential (Mandatory) Criteria:
| # | Criterion | Rationale |
|---|---|---|
| 1 | Autosomal recessive inheritance | Both parents are carriers; affected siblings, consanguinity may be present [1][2] |
| 2 | Onset before age 25 years | Classic FRDA is a paediatric-onset disease (now relaxed with recognition of late-onset forms, but the original criterion stands) |
| 3 | Progressive limb and gait ataxia | The core neurological feature — combined sensory + cerebellar ataxia |
| 4 | Absent knee and ankle jerks | DRG degeneration → loss of Ia afferent limb of the reflex arc |
| 5 | Electrophysiological evidence of axonal sensory neuropathy | Motor NCS normal but sensory nerve action potentials (SNAPs) are absent or severely reduced |
Harding Additional (Supportive) Criteria — present within 5 years of onset:
| Feature | Comment |
|---|---|
| Dysarthria | Scanning/cerebellar speech — from dentate nucleus degeneration |
| Extensor plantar responses (Babinski +) | Corticospinal tract involvement — the hallmark "mixed LMN + UMN" sign |
| Pes cavus | Foot muscle imbalance from denervation |
| Scoliosis | Paraspinal muscle weakness |
| Cardiomyopathy (ECG abnormalities) | T-wave inversions, LVH — hypertrophic cardiomyopathy |
High Yield — When to Suspect FRDA Clinically
Suspect Friedreich ataxia in any child or adolescent with: (1) progressive ataxia, (2) onset before 25 years, (3) absent lower limb reflexes, (4) extensor plantar responses, and (5) autosomal recessive family pattern. The presence of pes cavus, scoliosis, or cardiomyopathy further strengthens suspicion.
In current clinical practice (2024–2026), the diagnosis of FRDA is confirmed by genetic testing:
| Genotype | Frequency | Diagnostic Interpretation |
|---|---|---|
| Homozygous GAA expansion (both alleles ≥ 66 repeats in FXN intron 1) | ~96% of FRDA cases | Confirms diagnosis |
| Compound heterozygote (GAA expansion on one allele + point mutation / deletion on the other) | ~4% of FRDA cases | Confirms diagnosis — requires sequencing of FXN coding region if only one expanded allele found |
| One expanded allele only, no point mutation found | — | Does not confirm FRDA — consider alternative diagnoses or deep intronic / regulatory variants |
| No expanded alleles | — | Excludes FRDA — pursue other differential diagnoses |
Key principle: Friedreich ataxia is caused by GAA trinucleotide repeat expansion in the non-coding intron 1 of the FXN gene (chromosome 9q21). Homozygous expansion in ~96% of cases. Compound heterozygotes account for ~4%. [1][2][13]
| Repeat Size | Classification | Clinical Significance |
|---|---|---|
| 5–33 | Normal | No disease, not a carrier |
| 34–65 | Borderline / Premutation | Unclear clinical significance; may be unstable during transmission |
| ≥ 66 (typically 600–1200 in patients) | Full mutation / Pathogenic | Disease-causing when homozygous or compound heterozygous |
Severity depends on number of expansions: earlier onset and loss of ambulation, more cardiomyopathy with larger expansions. [13]
2. Diagnostic Algorithm
The diagnostic pathway for a paediatric patient with suspected FRDA involves:
- Clinical suspicion — based on history and examination findings
- Exclusion of treatable mimics — AVED, Wilson disease (as discussed in DDx section)
- Molecular genetic testing — the definitive diagnostic step
- Baseline assessment of multi-system involvement — cardiac, endocrine, skeletal, ophthalmological
Why exclude treatable mimics before genetic testing?
- Genetic testing may take weeks to return results
- If the child has AVED (vitamin E deficiency), every week of delay means ongoing neuronal damage that could have been prevented
- Wilson disease can cause irreversible neurological damage if untreated
- These screening tests (vitamin E, caeruloplasmin, slit-lamp) are cheap, fast, and widely available
Why sequence the coding region if only one expanded allele is found?
- ~4% of FRDA patients are compound heterozygotes — they carry a GAA expansion on one allele and a point mutation, missense mutation, or deletion on the other
- Standard GAA repeat analysis only detects expansions, NOT point mutations
- If you find one expanded allele in a patient with a convincing clinical picture, you must sequence the FXN coding region to look for the second pathogenic variant
3. Investigation Modalities — Detailed Findings and Interpretation
| Test | Method | Key Findings | Interpretation |
|---|---|---|---|
| GAA repeat analysis of FXN gene | Triplet-repeat primed PCR (TP-PCR) or Southern blot | Homozygous GAA expansion ≥ 66 repeats (typically 600–1200) | Diagnostic of FRDA in ~96% of cases |
| FXN gene sequencing | Sanger sequencing or next-generation sequencing of coding exons | Point mutation, missense, or small deletion on one allele | Confirms compound heterozygote FRDA (~4%) |
| MLPA or array CGH | Multiplex ligation-dependent probe amplification | Whole-exon or partial gene deletion | Rare cause of second allele pathogenicity |
Paediatric consideration: In Hong Kong, genetic testing for FRDA is available through referral centres (e.g., Clinical Genetic Service, Department of Health). Genetic counselling should be offered to the family before and after testing, covering implications for siblings (25% recurrence risk in AR), carrier testing, and prenatal diagnosis options.
Interpreting repeat sizes:
- The smaller of the two GAA alleles (GAA1) is the strongest predictor of disease severity and age of onset
- Why? Because the allele with the fewer repeats produces more residual frataxin than the allele with more repeats, so it is the "rate-limiting" allele
3.2 Neurophysiological Studies
| Parameter | Expected Finding in FRDA | Explanation |
|---|---|---|
| Sensory nerve action potentials (SNAPs) | Absent or severely reduced amplitude | DRG neuronal loss → axonal degeneration of sensory fibres → SNAP amplitude reflects axon number, not myelin. This is the earliest and most consistent electrophysiological abnormality |
| Sensory nerve conduction velocity | Normal or mildly reduced | Because this is an axonal (not demyelinating) process — the remaining axons conduct normally, but there are fewer of them |
| Motor nerve conduction | Normal or mildly reduced amplitude in late disease | Motor neurones (anterior horn cells) are relatively spared — corticospinal tract degeneration is a central (UMN) process, not peripheral |
| F-wave latencies | Normal or mildly prolonged | Minimal peripheral motor involvement |
Key NCS Interpretation
FRDA shows an axonal sensory neuropathy pattern: absent/reduced SNAPs with preserved motor conduction. This is one of Harding's essential diagnostic criteria. If motor NCS is markedly abnormal, reconsider the diagnosis (think CMT or other motor neuropathies).
| Finding | Interpretation |
|---|---|
| Usually normal or shows mild chronic denervation changes in distal muscles | Anterior horn cells are relatively preserved; any denervation is secondary and late |
| No active denervation (fibrillations/positive sharp waves) in early disease | Distinguishes from SMA (which shows florid denervation) |
| Finding | Interpretation |
|---|---|
| Absent or markedly delayed cortical potentials (especially from lower limbs) | Posterior column degeneration → impaired conduction of proprioceptive signals from periphery to cortex |
| More severely affected in lower limbs than upper limbs | Longer axonal pathway (fasciculus gracilis > cuneatus) → more vulnerable |
| Finding | Interpretation |
|---|---|
| May show prolonged latency or reduced amplitude | Optic nerve involvement (subclinical optic atrophy) — present in a subset of patients |
| Finding | Interpretation |
|---|---|
| Abnormal in many patients — absent or delayed waves | Auditory pathway (cochlear nerve / brainstem auditory nuclei) involvement. Often subclinical — patient may not notice hearing loss, but audiometric testing is abnormal |
3.3 Neuroimaging
| Finding | Interpretation |
|---|---|
| Often normal in early disease | Unlike SCAs where cerebellar atrophy is prominent early, FRDA predominantly affects spinal cord and DRG, NOT cerebellar cortex |
| Cerebellar atrophy may develop in late disease | Dentate nucleus degeneration ± secondary cortical atrophy over years |
| No white matter lesions | Distinguishes from MS, ADEM, leukodystrophies |
| No basal ganglia abnormalities | Distinguishes from Wilson disease (which shows T2-hyperintensity in putamen/caudate), mitochondrial disorders (basal ganglia necrosis) |
| Finding | Interpretation |
|---|---|
| Spinal cord atrophy (especially cervical cord) | Degeneration of posterior columns, spinocerebellar tracts, and corticospinal tracts → loss of white matter volume → visible cord thinning |
| No focal lesions or contrast enhancement | Distinguishes from demyelinating disease (MS plaques), tumours, or infections |
Why is the brain MRI often normal early but the spinal cord is atrophic? Because the primary pathology in FRDA is in the dorsal root ganglia, spinal cord tracts, and dentate nucleus — NOT the cerebellar cortex. The cerebellum loses its afferent input (from dead spinocerebellar tract axons) and its major output nucleus (dentate) but the cortex itself is relatively preserved.
| Finding | Interpretation |
|---|---|
| Left ventricular hypertrophy (concentric or asymmetric) | Hypertrophic cardiomyopathy — the most common cardiac phenotype |
| Myocardial iron deposition (T2* mapping — shortened T2*) | Direct evidence of mitochondrial iron accumulation in cardiomyocytes — correlates with disease severity |
| Late gadolinium enhancement (LGE) | Myocardial fibrosis — indicates irreversible damage; associated with progression to dilated cardiomyopathy |
| Reduced ejection fraction (in advanced disease) | Transition from HCM to dilated cardiomyopathy (DCM) |
3.4 Cardiac Investigations
| Finding | Frequency | Interpretation |
|---|---|---|
| T-wave inversions (especially in inferior and lateral leads) | Very common (~80%) | Often the earliest cardiac abnormality; reflects repolarisation abnormality from hypertrophied/fibrotic myocardium |
| Left ventricular hypertrophy (LVH) voltage criteria | Common | Increased LV mass |
| ST-segment changes | Variable | Subendocardial ischaemia in hypertrophied ventricle |
| Short PR interval | Some patients | May reflect enhanced AV conduction or pre-excitation (not classic WPW but short PR can occur) |
| Atrial fibrillation or flutter | Later disease | Atrial dilation from diastolic dysfunction |
| Ventricular ectopics | Variable | Arrhythmogenic substrate from fibrosis |
Paediatric note: ECG should be performed at diagnosis and then annually as part of cardiac surveillance. T-wave inversions may be the ONLY abnormality initially — do NOT dismiss them as "non-specific" in a child with ataxia.
| Finding | Interpretation |
|---|---|
| Concentric left ventricular hypertrophy (increased wall thickness > +2 SD z-score for age/BSA) | Hallmark finding — hypertrophic cardiomyopathy. Use paediatric z-scores (not adult absolute values) for wall thickness and LV mass |
| Preserved or supranormal LVEF (in HCM phase) | Diastolic dysfunction predominates initially; systolic function preserved |
| Diastolic dysfunction (impaired relaxation pattern on tissue Doppler) | Stiff, hypertrophied ventricle → impaired filling |
| Reduced LVEF (in later DCM phase) | Transition to dilated cardiomyopathy — poor prognosis |
| Dynamic LVOT obstruction (SAM of mitral valve) | If asymmetric septal hypertrophy causes outflow tract narrowing — less common than in sarcomeric HCM |
Paediatric Echo — Use Z-Scores
In paediatric cardiology, do NOT use adult absolute cutoff values for LV wall thickness or chamber dimensions. Instead, use age- and body-surface-area-corrected z-scores. An interventricular septum thickness z-score > +2 is considered hypertrophic. This is a common exam mistake.
| Finding | Interpretation |
|---|---|
| Supraventricular or ventricular arrhythmias | Risk stratification for sudden cardiac death |
| Atrial fibrillation (paroxysmal) | May be asymptomatic — Holter is needed to detect |
| Test | Expected Finding | Interpretation |
|---|---|---|
| Fasting glucose | May be elevated (> 5.6 mmol/L) | Screen for diabetes mellitus (β-cell dysfunction from oxidative stress) |
| HbA1c | May be elevated (≥ 5.7% / ≥ 39 mmol/mol) | Pre-diabetes or diabetes |
| Oral glucose tolerance test (OGTT) | Impaired glucose tolerance or diabetic pattern | More sensitive than fasting glucose alone — recommended as baseline and for surveillance |
| Serum vitamin E | Normal in FRDA | Excludes AVED (which is the treatable phenocopy) |
| Serum caeruloplasmin | Normal in FRDA | Excludes Wilson disease |
| 24-hour urine copper | Normal in FRDA | Excludes Wilson disease |
| Serum AFP | Normal in FRDA | Excludes ataxia-telangiectasia (where AFP is elevated) |
| Immunoglobulins (IgA, IgG subclasses) | Normal in FRDA | Excludes ataxia-telangiectasia (which has immunodeficiency) |
| Serum B12 | Normal in FRDA | Excludes subacute combined degeneration |
| Thyroid function tests (TFT) | Normal in FRDA | Excludes hypothyroidism as a cause of ataxia |
| Complete blood count (CBC) | Usually normal | Rule out anaemia; acanthocytes on film would suggest abetalipoproteinaemia |
| Fasting lipid profile | Usually normal | Very low cholesterol/TG → think abetalipoproteinaemia |
| Serum phytanic acid | Normal in FRDA | Excludes Refsum disease |
| Frataxin protein levels (research / specialised labs) | Markedly reduced (5–30% of normal) | Research tool; available in some centres. Can support diagnosis but is not the standard diagnostic test |
| Examination | Finding | Interpretation |
|---|---|---|
| Fundoscopy | Optic disc pallor (optic atrophy) in some patients | Optic nerve fibre degeneration — may be subclinical |
| Optical coherence tomography (OCT) | Retinal nerve fibre layer (RNFL) thinning | Quantitative measure of optic nerve degeneration — increasingly used in research |
| Visual acuity | May be reduced in advanced disease | Gradual visual decline from optic atrophy |
| Slit-lamp examination | Normal (no Kayser-Fleischer rings) | Confirms this is NOT Wilson disease |
| Test | Finding | Interpretation |
|---|---|---|
| Pure tone audiometry | Sensorineural hearing loss (variable severity) | Cochlear nerve / auditory pathway degeneration |
| Brainstem auditory evoked responses (BAERs) | Abnormal (as above) | Central auditory pathway involvement, often subclinical |
| Investigation | Finding | Interpretation |
|---|---|---|
| Spine X-ray (AP + lateral) | Scoliosis (may be significant enough to require Cobb angle measurement) | Progressive kyphoscoliosis — affects respiratory function if severe. Orthopaedic referral if Cobb angle > 20–25° |
| Foot X-ray | Pes cavus with hammer toes | Documented for baseline; may need orthotics or surgical correction |
| Test | Finding | Interpretation |
|---|---|---|
| Pulmonary function tests (spirometry) | Restrictive pattern (reduced FVC with preserved FEV1/FVC ratio) | Scoliosis → chest wall restriction + respiratory muscle weakness → reduced lung volumes |
| Nocturnal oximetry / polysomnography | Desaturations, hypoventilation | Late disease — may need non-invasive ventilation |
Once FRDA is genetically confirmed, multi-system assessment should be initiated and repeated at regular intervals. This is a multidisciplinary team (MDT) approach in paediatrics:
| System | Investigation | Frequency |
|---|---|---|
| Cardiac | ECG + Echocardiography (+ cardiac MRI if available) | At diagnosis, then annually |
| 24-hour Holter monitor | Annual or if symptomatic | |
| Endocrine | Fasting glucose + HbA1c + OGTT | At diagnosis, then annually |
| Neurological | Clinical neurological assessment + functional scales (FARS, mFARS, SARA) | Every 6–12 months |
| NCS (baseline) | At diagnosis | |
| MRI spinal cord (baseline) | At diagnosis | |
| Skeletal | Spine X-ray / clinical scoliosis assessment | At diagnosis, then annually (especially pre/peri-pubertal growth spurt) |
| Ophthalmology | Visual acuity + fundoscopy ± OCT ± VEPs | At diagnosis, then annually |
| Audiology | Pure tone audiometry ± BAERs | At diagnosis, then as indicated |
| Respiratory | Spirometry (from age ~6 years when cooperation allows) | Annual (especially if scoliosis present) |
| Growth | Height, weight, BMI, pubertal staging | Every clinic visit |
Family-Centred Care — Paediatric Emphasis
After genetic confirmation:
- Genetic counselling for the entire family — carrier testing for siblings, reproductive options for parents, prenatal diagnosis discussion
- Psychological support for the child and family — adjustment to chronic progressive disability
- School liaison — educational support, exam accommodations, wheelchair access
- Physiotherapy and occupational therapy — maximise function, prevent contractures
- Transition planning — begin discussing transition to adult services from early adolescence
| Step | What to Do | What You're Looking For |
|---|---|---|
| 1. Clinical suspicion | History + neurological exam + cardiac auscultation + skeletal exam | Progressive ataxia + areflexia + upgoing plantars + pes cavus + scoliosis ± murmur |
| 2. Exclude treatable mimics | Vitamin E, caeruloplasmin, slit-lamp, B12 | Normal in FRDA; abnormal → treat the mimic |
| 3. Genetic confirmation | FXN GAA repeat analysis → if one allele expanded, sequence coding region | Homozygous expansion (96%) or compound heterozygote (4%) |
| 4. Baseline multi-system assessment | ECG, echo, glucose/HbA1c/OGTT, NCS, MRI spine, scoliosis X-ray, ophthalmology, audiology | HCM, diabetes/prediabetes, axonal sensory neuropathy, cord atrophy, scoliosis, optic atrophy |
| 5. Ongoing surveillance | Annual cardiac + endocrine + skeletal + functional assessment | Detect progression, guide intervention |
High Yield Summary — Diagnosis of Friedreich Ataxia
- Diagnosis is confirmed by genetic testing — GAA trinucleotide repeat expansion in FXN gene (chromosome 9q21), ≥ 66 repeats on both alleles (homozygous, 96%) or one expanded allele + point mutation (compound heterozygote, 4%)
- Harding essential criteria (clinical suspicion): AR inheritance, onset before 25 years, progressive ataxia, absent knee and ankle jerks, axonal sensory neuropathy on NCS
- NCS shows axonal sensory neuropathy: absent or severely reduced SNAPs with normal motor conduction — an essential diagnostic criterion
- ECG abnormalities (T-wave inversions, LVH) are often the earliest cardiac sign — do NOT dismiss in a child with ataxia
- Echocardiography shows concentric LVH using paediatric z-scores (not adult cutoffs)
- MRI brain is often normal early (unlike SCAs); MRI spinal cord shows cervical cord atrophy
- Always exclude treatable mimics first: serum vitamin E (AVED), caeruloplasmin/slit-lamp (Wilson), B12
- The smaller GAA allele (GAA1) best predicts age of onset and severity
- Larger GAA repeat size → earlier onset, more severe disease, more cardiomyopathy [13]
- Multi-system annual surveillance (cardiac, endocrine, skeletal, respiratory, ophthalmology, audiology) is mandatory after diagnosis
Active Recall — Diagnosis of Friedreich Ataxia
[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p497 — Trinucleotide repeat expansion mutation section) [2] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p881 — Genetics of Fragile X syndrome / Triplet expansion disorders) [3] Senior notes: Ryan Ho Neurology.pdf (p117 — Approach to Cerebellar Syndrome, Aetiology table) [4] Senior notes: Ryan Ho Fundamentals.pdf (p333 — Cerebellar Syndrome, D/dx of cerebellar ataxia) [5] Lecture slides: CFB_Neuro clinical skills demonstration_01.08.22_file to students.pdf (p7–8 — Where / What is the lesion) [13] Senior notes: Maksim Medicine Notes.pdf (p254 — Friedreich's ataxia genetics, severity depends on number of expansions)
Friedreich Ataxia — Management Algorithm & Treatment Modalities
1. Principles of Management
There is currently no cure for Friedreich ataxia. Until very recently, management was entirely supportive and symptomatic. However, in 2023 the first disease-modifying therapy — omaveloxolone (Skyclarys®) — was approved by the FDA, representing a paradigm shift.
Management of Friedreich ataxia is supportive. [14]
Despite this historic teaching point, the management framework in 2025–2026 has evolved to include:
- Disease-modifying pharmacotherapy (omaveloxolone — approved FDA 2023, EMA 2024)
- Symptomatic and supportive multidisciplinary care (the backbone of management)
- Surveillance and prevention of complications (cardiac, endocrine, skeletal, respiratory)
- Genetic counselling and family-centred care (central to paediatric practice)
- Emerging therapies (gene therapy, frataxin replacement — investigational)
FRDA is a multi-system disease affecting the nervous system, heart, endocrine pancreas, skeleton, eyes, and ears. No single specialist can manage all aspects. The paediatric MDT should include:
| Team Member | Role |
|---|---|
| Paediatric neurologist (lead clinician) | Neurological assessment, disease-modifying therapy, functional monitoring, coordination of care |
| Paediatric cardiologist | Cardiac surveillance (echo, ECG, Holter), management of HCM/arrhythmias/heart failure |
| Paediatric endocrinologist | Diabetes screening and management |
| Orthopaedic surgeon | Scoliosis management (bracing, surgery), foot deformities |
| Physiotherapist | Gait training, balance exercises, prevention of contractures, wheelchair skills |
| Occupational therapist | Adaptive equipment, ADL strategies, upper limb function |
| Speech and language therapist | Dysarthria management, swallowing assessment (dysphagia), communication aids |
| Ophthalmologist | Visual surveillance |
| Audiologist | Hearing surveillance and aids |
| Clinical psychologist / psychiatrist | Adjustment to chronic illness, depression, anxiety, family support |
| Social worker | Disability support, school accommodations, financial assistance |
| Clinical geneticist / genetic counsellor | Family counselling, sibling testing, reproductive options |
| Respiratory physician | PFTs, NIV when needed (late disease) |
3. Treatment Modalities — Detailed
3.1 Disease-Modifying Therapy
This is the first and currently only FDA-approved disease-modifying therapy for Friedreich ataxia (approved February 2023; EMA approved February 2024).
Drug name breakdown:
- "Omaveloxolone" — a synthetic oleanane triterpenoid (derived from oleanolic acid, found in olive leaves)
- Brand name: Skyclarys®
Mechanism of action — explained from first principles:
- FRDA causes frataxin deficiency → mitochondrial iron accumulation → massive ROS production → oxidative cell death
- Normally, cells defend against oxidative stress using the Nrf2 (nuclear factor erythroid 2-related factor 2) pathway:
- Nrf2 is a transcription factor that activates genes encoding antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase, heme oxygenase-1)
- Under normal conditions, Nrf2 is kept inactive by its inhibitor Keap1 (Kelch-like ECH-associated protein 1)
- Under oxidative stress, Nrf2 is released from Keap1, translocates to the nucleus, and activates the antioxidant response element (ARE) — upregulating protective genes
- In FRDA, the Nrf2 pathway is impaired — despite massive oxidative stress, the cells cannot mount an adequate antioxidant defence
- Omaveloxolone activates Nrf2 by inhibiting the Keap1-Nrf2 interaction → releases Nrf2 → enhances transcription of antioxidant and anti-inflammatory genes → reduces oxidative damage to neurones and cardiomyocytes
| Parameter | Detail |
|---|---|
| Class | Nrf2 activator (antioxidant pathway enhancer) |
| Route | Oral (capsule) |
| Dose | 150 mg once daily on an empty stomach (≥ 1 hour before or 2 hours after food) |
| Approved age | ≥ 16 years (FDA); adolescents ≥ 16 years can be started in paediatric services |
| Evidence | MOXIe trial (Phase 2, randomised, double-blind): showed statistically significant improvement in modified Friedreich Ataxia Rating Scale (mFARS) score at 48 weeks compared to placebo. Mean improvement ~2.4 points on mFARS |
| Effect | Slows neurological progression; does NOT reverse existing damage or restore frataxin levels |
Key side effects and monitoring:
| Side Effect | Mechanism | Monitoring |
|---|---|---|
| Elevated transaminases (ALT/AST) | Drug-induced hepatotoxicity — dose-dependent | LFTs at baseline, monthly for first 3 months, then every 3 months. Discontinue if ALT/AST > 5× ULN or if clinical signs of liver injury |
| Elevated BNP / NT-proBNP | Fluid retention, Nrf2 effects on natriuretic peptide metabolism | Monitor BNP; assess for clinical heart failure |
| Decreased body weight | Appetite suppression | Monitor weight at each visit (especially important in adolescents — growth impact) |
| Headache, nausea, abdominal pain | GI intolerance | Symptomatic management |
| Reduced LVEF | Rare but reported — unclear mechanism | Echocardiography surveillance |
Contraindications and cautions:
| Contraindication / Caution | Rationale |
|---|---|
| Concomitant moderate-to-strong CYP3A4 inhibitors | Omaveloxolone is metabolised by CYP3A4; inhibitors (e.g., ketoconazole, clarithromycin, grapefruit juice) increase drug exposure and toxicity risk |
| Avoid with strong CYP3A4 inducers | Reduces drug levels (e.g., rifampicin, phenytoin, carbamazepine) |
| Hepatic impairment | Hepatotoxicity risk; avoid if baseline ALT/AST significantly elevated |
| Pregnancy | Insufficient safety data; effective contraception required |
| Age < 16 years | Not yet approved; clinical trials ongoing for younger paediatric patients |
Paediatric Prescribing Note
Omaveloxolone is approved for age ≥ 16 years only. For children < 16, it is NOT yet licensed. Clinical trials (e.g., MOXIe-Pediatric) are underway. Do NOT prescribe off-label in younger children without specialist guidance and ideally within a clinical trial framework. Always check for drug interactions — many anti-epileptic drugs are CYP3A4 inducers and would reduce efficacy.
| Parameter | Detail |
|---|---|
| Class | Synthetic analogue of coenzyme Q10 (ubiquinone) |
| Mechanism | Electron carrier in the mitochondrial respiratory chain; antioxidant |
| Evidence | Multiple clinical trials (IONIA, NICOSIA, MICONOS) showed inconsistent results — some showed cardiac benefit (reduced LV mass) but no consistent neurological benefit |
| Current status | NOT recommended by most international guidelines. Was never FDA-approved for FRDA. Some centres still use it off-label for cardiac protection, but evidence is weak |
| Why mentioned | Still appears in older textbooks and may be referenced in exams — students should know it was tried but is not standard of care |
| Parameter | Detail |
|---|---|
| Rationale | Both are antioxidants; theoretical benefit in reducing mitochondrial oxidative stress |
| Evidence | Small studies showed possible cardiac benefit (reduced LV hypertrophy) but no convincing neurological benefit in clinical trials |
| Current status | Not standard of care; sometimes used as adjunctive therapy by individual centres |
3.2 Symptomatic and Supportive Treatment — By System
This is the cornerstone of management regardless of disease-modifying therapy.
| Intervention | Purpose | Detail |
|---|---|---|
| Physiotherapy | Maintain mobility, balance, strength | Regular sessions (2–3× weekly); focus on gait training, balance exercises, stretching to prevent contractures, core strengthening. Hydrotherapy (aquatic therapy) is particularly beneficial — buoyancy reduces fall risk while exercising |
| Aerobic exercise programme | Maintain cardiovascular fitness, delay functional decline | Moderate-intensity exercise is safe and beneficial in FRDA (unlike historical advice to avoid exercise). Swimming, stationary cycling, seated exercises recommended. Monitor with cardiac clearance |
| Occupational therapy | Maintain independence in ADLs | Adaptive devices (modified cutlery, writing aids, dressing aids), home modifications (grab rails, wheelchair ramps), computer access technology |
| Wheelchair assessment | Mobility when walking becomes unsafe | Timely provision is important — delaying wheelchair prescription leads to falls and fractures. Power wheelchair usually needed (upper limb ataxia makes manual wheelchair difficult). Typically needed ~10–15 years after onset |
| Assistive technology | Communication and education | Speech-generating devices when dysarthria becomes severe; adapted computer interfaces for school work |
| Anti-spasticity agents (late disease) | Manage lower limb spasticity | Baclofen (oral or intrathecal), tizanidine — used when spasticity becomes functionally limiting or painful. Start low, titrate slowly. Baclofen paediatric dose: 0.75–2 mg/kg/day in divided doses |
Exercise in FRDA — Important Teaching Point
Historically, patients with FRDA were told to "rest" and avoid exertion. This is now known to be wrong. Current evidence supports regular, moderate aerobic and resistance exercise as beneficial for cardiovascular fitness, functional capacity, and potentially mitochondrial function. Exercise should be prescribed with cardiac clearance and supervision.
The heart is the primary target organ for mortality. Management depends on the cardiac phenotype:
| Stage | Management | Rationale |
|---|---|---|
| Asymptomatic HCM | ACE inhibitor or ARB (e.g., enalapril, losartan) | Reduce cardiac workload, attenuate LVH, reduce fibrosis. Enalapril paediatric dose: 0.08–0.1 mg/kg/dose once or twice daily, titrate to effect |
| HCM with LVOT obstruction | Beta-blocker (e.g., propranolol, metoprolol) | Reduce heart rate → longer diastolic filling → reduce dynamic LVOT gradient. Avoid vasodilators (which worsen obstruction) |
| Symptomatic heart failure (reduced EF) | Standard HF therapy: ACE-I/ARB + beta-blocker + diuretics | Transition to dilated cardiomyopathy — treat as per paediatric heart failure guidelines. May need digoxin, spironolactone. Consider referral for cardiac transplantation in refractory cases |
| Arrhythmias (AF, VT) | Anti-arrhythmic therapy; DC cardioversion if haemodynamically unstable; anticoagulation for AF | Rate or rhythm control depending on clinical scenario |
| High risk of sudden cardiac death | ICD (implantable cardioverter-defibrillator) | If sustained VT, VF, or high-risk features on Holter. Decision made in conjunction with paediatric electrophysiologist |
| End-stage heart failure | Cardiac transplantation | Considered in selected patients with refractory heart failure. FRDA-specific considerations: progressive neurological disability may affect transplant candidacy — ethical discussions needed |
Drugs to AVOID in FRDA cardiomyopathy:
| Drug | Why Avoid |
|---|---|
| Verapamil / Diltiazem | Negative inotropes — risk of worsening heart failure in patients with impaired systolic function |
| Nifedipine and other vasodilators (in obstructive HCM) | Reduce afterload → worsen dynamic LVOT obstruction |
| NSAIDs (regular use) | Fluid retention, renal impairment, interact with ACE-I/ARB |
| Scenario | Management |
|---|---|
| Impaired glucose tolerance | Dietary modification (reduce refined carbohydrates), regular exercise, weight management. Metformin may be considered — paediatric dose: 500 mg once daily, titrate to 500 mg BD or TDS (max 2 g/day). Metformin has additional theoretical mitochondrial benefits |
| Overt diabetes mellitus — predominantly insulin deficiency | Insulin therapy — often required because FRDA diabetes has a significant β-cell failure component (unlike typical type 2 DM). May need basal-bolus insulin regimen similar to type 1 DM management |
| Mixed insulin resistance + deficiency | Combination: metformin + insulin |
| Monitoring | Self-monitoring of blood glucose, HbA1c every 3 months, annual retinal screening, annual renal function/microalbumin |
Why does FRDA diabetes differ from typical type 1 or type 2? FRDA diabetes is caused by pancreatic β-cell oxidative destruction (mitochondrial-mediated) — resulting in insulin deficiency (like type 1). However, there may also be peripheral insulin resistance (like type 2). It is therefore a mixed picture. Treatment must be individualised — some patients need insulin from the outset, others can be managed initially with metformin.
| Problem | Management | When |
|---|---|---|
| Scoliosis — mild (Cobb angle < 20°) | Observation and clinical surveillance every 6 months | Monitor especially during pubertal growth spurt (rapid progression risk) |
| Scoliosis — moderate (Cobb 20–40°) | Bracing (thoracolumbosacral orthosis, TLSO) | Aim to slow progression; most effective in skeletally immature children |
| Scoliosis — severe (Cobb > 40–50°) or rapidly progressive | Spinal fusion surgery | Prevents further curve progression, improves sitting posture (for wheelchair users), and preserves respiratory function. Surgical timing must balance skeletal maturity vs curve progression |
| Pes cavus — mild | Custom orthotics (insoles, ankle-foot orthoses) | Improve comfort and gait stability |
| Pes cavus — severe, with pain or skin breakdown | Surgical correction (soft tissue releases, osteotomies, tendon transfers) | When orthotics fail |
| Problem | Management |
|---|---|
| Dysarthria | Speech therapy — exercises to strengthen orofacial muscles, slow speech rate strategies, augmentative and alternative communication (AAC) devices when speech becomes unintelligible |
| Dysphagia (late disease) | Videofluoroscopic swallowing study (VFSS) to assess; texture-modified diet (thickened fluids, soft foods); positioning advice; supervised feeding. If severe/unsafe swallowing → nasogastric tube or percutaneous gastrostomy (PEG) |
| Nutritional deficiency | Dietetic input — ensure adequate caloric intake (difficult with dysphagia), micronutrient supplementation |
| Problem | Management |
|---|---|
| Restrictive lung disease (from scoliosis + respiratory muscle weakness) | Annual spirometry; chest physiotherapy; respiratory muscle training |
| Nocturnal hypoventilation | Nocturnal oximetry/capnography screening → non-invasive ventilation (NIV, e.g., BiPAP) if nocturnal desaturation or hypercapnia |
| Respiratory infections | Aggressive treatment (antibiotics, chest physiotherapy); influenza and pneumococcal vaccination |
| Aspect | Approach |
|---|---|
| Adjustment to diagnosis | Age-appropriate explanation of condition; involve child in discussions (assent); use visual aids for younger children |
| Depression and anxiety | Screen at every clinic visit; CBT or supportive psychotherapy; SSRIs if needed (fluoxetine from age 8 years — paediatric licensed) |
| School support | Liaise with school for accommodations — extra time for exams, scribe, wheelchair access, adapted PE |
| Peer support | Connect with patient organisations (e.g., Friedreich's Ataxia Research Alliance, Ataxia UK — no HK-specific organisation but international resources available) |
| Sibling support | Siblings may experience guilt, anxiety, or neglect — include them in family sessions |
| Aspect | Detail |
|---|---|
| Inheritance pattern | AR — both parents are obligate carriers |
| Recurrence risk | Each pregnancy: 25% affected, 50% carrier, 25% unaffected non-carrier |
| Carrier testing for siblings | Offered to all siblings — important for reproductive planning |
| Prenatal diagnosis | Available by chorionic villus sampling (CVS) at 10–12 weeks or amniocentesis at 15–18 weeks — test for GAA expansion |
| Preimplantation genetic testing (PGT) | Available for couples who are both carriers — IVF with embryo selection for unaffected embryos |
| Consent/assent | In paediatrics, genetic testing of a child should be for the child's direct medical benefit. Predictive carrier testing of minors for reproductive purposes is generally deferred until the individual can provide autonomous consent (≥ 16–18 years) |
| Aspect | Approach |
|---|---|
| When to begin | Discussions should start at age 12–14 years |
| Key elements | Self-management education (medications, symptoms), understanding own condition, appointment management, knowing when to seek help |
| Transfer | Usually at age 16–18 years to adult neurology, cardiology, and endocrinology services, depending on local arrangements |
| Challenges | Loss of continuity, different care philosophy (paediatrics = family-centred vs adult = individual-centred), gaps in MDT support |
These are NOT standard of care but are important to know as a medical student, as they represent the future direction of FRDA treatment.
| Therapy | Mechanism | Status (2025–2026) |
|---|---|---|
| Gene therapy | AAV-based delivery of functional FXN gene to cells → restore frataxin production | Phase 1/2 clinical trials (e.g., LX2006 by Lexeo Therapeutics — intracardiac delivery for cardiac FRDA) |
| Frataxin protein replacement | Direct delivery of recombinant frataxin protein (e.g., CTI-1601) | Phase 1/2 trials — subcutaneous frataxin showed increased frataxin levels in blood cells |
| Frataxin gene reactivation (epigenetic approaches) | HDAC inhibitors (e.g., nicotinamide / niacinamide) — reverse heterochromatin silencing of FXN gene → ↑ frataxin transcription | Nicotinamide at high doses showed modest frataxin increase in Phase 2 trials; ongoing research |
| Interferon gamma | Upregulates frataxin expression via JAK-STAT pathway | Small studies showed frataxin increase; larger trials ongoing |
| Etravirine (repurposed antiretroviral) | Increases frataxin protein levels via unclear mechanism (possibly stabilises mRNA) | Early-phase investigation |
| Deuterated polyunsaturated fatty acids (RT001) | Reduce lipid peroxidation — protect cell membranes from ROS damage | Phase 2/3 trials |
| Iron chelation (deferiprone) | Remove excess mitochondrial iron → reduce Fenton reaction → ↓ ROS | Mixed results — some cardiac benefit but risk of systemic iron depletion (anaemia). Not standard of care — use only in clinical trials |
Iron Chelation — A Cautionary Note
Although mitochondrial iron overload is central to FRDA pathophysiology, systemic iron chelation with deferiprone must be used with extreme caution. Unlike haemochromatosis (where total body iron is elevated), in FRDA the total body iron is NORMAL — iron is simply misdistributed (accumulating in mitochondria, depleted in cytoplasm). Aggressive chelation causes systemic iron depletion → anaemia, neutropaenia. This is a common exam misconception.
| Priority | Intervention | Rationale |
|---|---|---|
| 1. Disease-modifying | Omaveloxolone (≥ 16 years) | Only approved therapy to slow neurological progression |
| 2. Cardiac surveillance + treatment | Annual echo/ECG; ACE-I/ARB for HCM; HF therapy if needed | Cardiomyopathy is the #1 cause of death |
| 3. Rehabilitation | PT, OT, speech therapy, wheelchair | Maximise function and independence |
| 4. Endocrine | Annual glucose/HbA1c/OGTT; metformin or insulin | Diabetes affects 10–30% of patients |
| 5. Orthopaedic | Scoliosis surveillance, bracing/surgery; foot orthotics | Prevent respiratory compromise, maintain sitting balance |
| 6. Psychological | Depression/anxiety screening, family support | Chronic progressive disability — high psychosocial burden |
| 7. Genetic counselling | Carrier testing, reproductive options | AR inheritance — 25% recurrence risk per pregnancy |
| 8. Transition | Begin at 12–14 years, transfer at 16–18 years | Ensure continuity of multi-system care into adulthood |
High Yield Summary — Management of Friedreich Ataxia
- Management has traditionally been supportive [14] — but omaveloxolone (Nrf2 activator) is now the first FDA-approved disease-modifying therapy (approved ≥ 16 years, 150 mg daily oral)
- Omaveloxolone slows neurological decline but does NOT cure or reverse existing damage; monitor LFTs monthly then quarterly
- Cardiac management is the most critical aspect — cardiomyopathy is the leading cause of death. ACE-I/ARB for HCM; standard HF therapy if DCM develops; ICD for high-risk arrhythmias
- FRDA diabetes is a mixed picture (β-cell destruction + insulin resistance) — may need insulin early (unlike typical T2DM)
- Rehabilitation (PT, OT, speech therapy) is the backbone of care at ALL stages — exercise is beneficial, not harmful
- Scoliosis must be monitored aggressively during pubertal growth spurt — brace if 20–40°, surgical fusion if > 40–50° or rapidly progressive
- Iron chelation is NOT standard of care — total body iron is normal; only mitochondrial iron is misdistributed
- Genetic counselling is essential: AR, 25% recurrence risk, prenatal diagnosis and PGT available
- Family-centred care with psychological support, school liaison, and transition planning from age 12–14 years
Active Recall — Management of Friedreich Ataxia
[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p497 — Trinucleotide repeat expansion mutation section) [2] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p881 — Genetics of Fragile X syndrome / Triplet expansion disorders) [3] Senior notes: Ryan Ho Neurology.pdf (p117 — Approach to Cerebellar Syndrome, Aetiology table: Hereditary — Friedreich's ataxia) [13] Senior notes: Maksim Medicine Notes.pdf (p254 — Friedreich's ataxia genetics, severity depends on number of expansions) [14] Senior notes: Adrian Lui Pediatrics Notes.pdf (p129 — Hereditary Ataxia: Friedreich's ataxia — Mx: supportive)
Friedreich Ataxia — Complications
Friedreich ataxia is a relentlessly progressive multi-system disease. Understanding its complications requires revisiting the core pathophysiology: frataxin deficiency → mitochondrial iron accumulation → oxidative stress → selective cell death in tissues with high metabolic demand. Complications arise from progressive damage to these vulnerable tissues and from the secondary consequences of immobility and chronic disability.
The complications can be organised into:
- Cardiac complications (the leading cause of death)
- Neurological complications (the leading cause of disability)
- Endocrine complications (diabetes and its sequelae)
- Orthopaedic complications (scoliosis, foot deformity)
- Respiratory complications (often the final common pathway)
- Complications of immobility (secondary to wheelchair dependence)
- Psychosocial complications (enormous burden in paediatric patients)
- Treatment-related complications (omaveloxolone, surgical)
2. Cardiac Complications
Cardiomyopathy is the most common cause of death in Friedreich ataxia. [14]
| Aspect | Detail |
|---|---|
| Frequency | Present in ~60–80% of FRDA patients |
| Pathophysiology | Frataxin deficiency → mitochondrial iron overload in cardiomyocytes → ROS generation → compensatory hypertrophy (initially adaptive, later maladaptive) → concentric LVH → diastolic dysfunction (stiff ventricle cannot relax properly → impaired filling → ↓ cardiac output on exertion) |
| Clinical consequence | Initially asymptomatic → exertional dyspnoea → exercise intolerance → eventually symptomatic heart failure |
| Paediatric importance | HCM may be the first detectable abnormality — ECG changes (T-wave inversions, LVH criteria) or echo findings may precede neurological symptoms in some children |
Why does HCM develop rather than DCM initially?
- In the early phase, cardiomyocytes are stressed but still viable → they hypertrophy as a compensatory response to impaired energy production (trying to maintain contractile force with more muscle mass)
- This is similar to how skeletal muscle hypertrophies under resistance training — except here the stimulus is pathological
| Aspect | Detail |
|---|---|
| Pathophysiology | As oxidative damage progresses → cardiomyocyte death → replacement fibrosis → the ventricle thins, dilates, and loses contractile function → systolic heart failure |
| Clinical consequence | Reduced LVEF → symptoms of congestive heart failure: dyspnoea at rest, orthopnoea, peripheral oedema, hepatomegaly (in children, hepatomegaly is a more prominent early sign of right heart failure than peripheral oedema) |
| Prognosis | Transition from HCM → DCM indicates a poor prognosis — end-stage cardiac disease |
| Management | Standard heart failure therapy: ACE-I/ARB + beta-blocker + diuretics ± digoxin. Consider cardiac transplantation referral in refractory cases |
| Arrhythmia | Mechanism | Clinical Impact |
|---|---|---|
| Atrial fibrillation / flutter | Atrial dilation from diastolic dysfunction → altered atrial electrophysiology → re-entrant circuits | Palpitations, haemodynamic compromise (loss of atrial kick is particularly harmful in a non-compliant ventricle), thromboembolic risk (stroke) |
| Supraventricular tachycardia | Atrial stretch and fibrosis | Palpitations, syncope |
| Ventricular tachycardia / fibrillation | Myocardial fibrosis creates arrhythmogenic substrate → re-entry circuits in ventricular myocardium | Sudden cardiac death — the most feared complication. May be the first manifestation in previously asymptomatic patients |
| Conduction abnormalities | Fibrosis of the conduction system (His bundle, bundle branches) | Heart block — may require pacemaker |
Sudden Cardiac Death in FRDA — Must Know
Sudden cardiac death from ventricular arrhythmias can occur at any age, including in childhood and adolescence, even before significant neurological disability develops. This is why annual cardiac surveillance (ECG + echo + Holter) is mandatory from the time of diagnosis. An ICD should be considered in patients with high-risk features (sustained VT, severely reduced LVEF, unexplained syncope).
- ~60% of FRDA patients die from cardiac causes: either progressive heart failure or sudden arrhythmic death
- Mean age of death: ~35–40 years (range 20s–60s; larger GAA repeats → earlier cardiac death)
- In paediatric patients, cardiac death can occur in the late teens or twenties — emphasising the need for aggressive cardiac monitoring from childhood
3. Neurological Complications
| Aspect | Detail |
|---|---|
| Timeline | Most patients become wheelchair-dependent within 10–15 years of symptom onset (typically by age 15–25 years) |
| Mechanism | Progressive combined sensory ataxia (posterior column degeneration) + cerebellar ataxia (spinocerebellar tract + dentate nucleus) + corticospinal tract degeneration → loss of balance, coordination, and eventually strength |
| Consequence | Loss of independence, requirement for full-time wheelchair, dependence on carers for all mobility. Major psychological impact, especially in adolescents |
| Mitigation | Physiotherapy to maintain mobility as long as possible; timely wheelchair provision (delaying wheelchair → falls → fractures) |
| Aspect | Detail |
|---|---|
| Progression | Scanning cerebellar dysarthria → progressively unintelligible speech → eventual anarthria (complete loss of speech) in some patients |
| Impact | Social isolation, frustration, impaired education, reduced quality of life |
| Mechanism | Dentate nucleus degeneration → impaired coordination of orofacial musculature, tongue, palate, and respiratory muscles during speech |
| Management | Speech therapy; augmentative and alternative communication (AAC) devices — e.g., tablet-based speech-generating applications; eye-gaze technology in severe cases |
| Aspect | Detail |
|---|---|
| Mechanism | Progressive bulbar and cerebellar dysfunction → impaired coordination of swallowing phases (oral preparatory, oral propulsive, pharyngeal) → coughing, choking, silent aspiration |
| Complications | Aspiration pneumonia — a significant cause of morbidity and mortality. Also leads to malnutrition and dehydration |
| Assessment | Videofluoroscopic swallowing study (VFSS) or fibreoptic endoscopic evaluation of swallowing (FEES) |
| Management | Texture-modified diet (thickened fluids, pureed foods); postural strategies during eating (chin tuck); supervised meals. If unsafe swallowing → PEG (percutaneous endoscopic gastrostomy) tube feeding |
| Aspect | Detail |
|---|---|
| Frequency | Occurs in a subset of patients (~10–30%) |
| Mechanism | Degeneration of retinal ganglion cell axons (optic nerve fibres) — similar mechanism to other mitochondrial optic neuropathies (e.g., Leber hereditary optic neuropathy) |
| Impact | Gradual visual loss → difficulty reading, recognising faces. Adds to functional disability in a patient who already has impaired fine motor skills |
| Aspect | Detail |
|---|---|
| Frequency | Subclinical auditory neuropathy in many patients; clinically significant hearing loss in ~10–20% |
| Mechanism | Degeneration of cochlear nerve (auditory nerve) and/or brainstem auditory pathways |
| Impact | Difficulty with communication (compounding dysarthria), social isolation |
| Management | Hearing aids; FM systems for school; cochlear implant consideration in severe cases (efficacy variable due to neural component) |
| Aspect | Detail |
|---|---|
| Frequency | Develops in later disease stages (~20–40% of patients) |
| Mechanism | Degeneration of autonomic pathways in the spinal cord → detrusor-sphincter dyssynergia or neurogenic bladder |
| Symptoms | Urgency, frequency, incontinence, or urinary retention |
| Management | Bladder training; anticholinergics (oxybutynin) for overactive bladder; intermittent catheterisation for retention |
4.1 Diabetes Mellitus
| Aspect | Detail |
|---|---|
| Frequency | ~10–30% of FRDA patients develop overt diabetes; an additional ~20–30% have impaired glucose tolerance |
| Mechanism | Oxidative destruction of pancreatic β-cells (mitochondrial iron overload in β-cells → ROS → apoptosis) → insulin deficiency (resembling type 1 DM) + possible peripheral insulin resistance (resembling type 2 DM). The result is a mixed picture |
| Complications of the diabetes itself | Microvascular: retinopathy, nephropathy, neuropathy [15]. Macrovascular: ischaemic heart disease, peripheral vascular disease, cerebrovascular disease [15]. These are superimposed on the pre-existing FRDA cardiomyopathy and neuropathy — compounding the disease burden |
| Screening | Annual fasting glucose + HbA1c ± OGTT from time of FRDA diagnosis. For pre-pubertal patients with DM, screen annually after 5 years of diabetes [16] |
| Management | Dietary modification; metformin if insulin resistance predominates; insulin if β-cell failure predominates (often needed early). HbA1c target individualised — typically < 7% (< 53 mmol/mol) but balance against hypoglycaemia risk in a neurologically impaired child |
Double Hit — Neuropathy in FRDA + Diabetes
FRDA patients who develop diabetes experience a "double hit" to their peripheral nerves — the pre-existing axonal sensory neuropathy from DRG degeneration is compounded by diabetic neuropathy (both small and large fibre). This accelerates sensory loss, increases fall risk, and makes foot care critical (risk of undetected ulcers on already deformed feet).
5. Orthopaedic Complications
| Aspect | Detail |
|---|---|
| Frequency | Present in ~60–80% of patients |
| Mechanism | Paraspinal muscle weakness and asymmetric innervation → imbalanced forces on the growing spine → progressive curvature. Worsens rapidly during the pubertal growth spurt |
| Complications of scoliosis itself | Restrictive lung disease (reduced chest wall compliance → ↓ FVC), chronic back pain, impaired sitting balance in wheelchair, cosmetic deformity, skin breakdown over prominent bony points |
| Management | Bracing (TLSO) for curves 20–40°; spinal fusion surgery for curves > 40–50° or rapidly progressive curves |
| Aspect | Detail |
|---|---|
| Frequency | Present in ~55–75% |
| Mechanism | Intrinsic foot muscle weakness from denervation → imbalance with preserved extrinsic muscles → arch elevation, hammer toes, metatarsal head prominence |
| Complications | Pressure sores on prominent metatarsal heads (especially when combined with diabetic neuropathy → loss of protective sensation), difficulty with footwear, abnormal gait biomechanics accelerating falls |
| Management | Custom orthotics; appropriate footwear; surgical correction (osteotomies, tendon transfers) if severe |
| Aspect | Detail |
|---|---|
| Mechanism | Progressive ataxia → frequent falls (especially before wheelchair use) + possible osteoporosis (reduced weight-bearing, vitamin D deficiency from reduced outdoor activity, endocrine dysfunction) |
| Common sites | Wrists (FOOSH — fall on outstretched hand), hips, vertebral compression fractures |
| Prevention | Timely wheelchair provision; physiotherapy for balance; bone health assessment (vitamin D, calcium intake); fall-proofing the home environment |
6. Respiratory Complications
| Aspect | Detail |
|---|---|
| Mechanism | Kyphoscoliosis → reduced chest wall compliance + respiratory muscle weakness (diaphragm and intercostal muscles) + reduced exercise → progressive restrictive ventilatory defect |
| Spirometry | Reduced FVC and TLC with preserved FEV₁/FVC ratio (restrictive pattern) |
| Clinical consequence | Reduced respiratory reserve → vulnerability to respiratory infections → respiratory failure |
| Aspect | Detail |
|---|---|
| Mechanism | Dysphagia → silent aspiration of oral contents into the lower airways → chemical pneumonitis → secondary bacterial pneumonia |
| Organisms | Oral anaerobes, Streptococcus species, gram-negative rods |
| Prevention | Swallowing assessment, texture-modified diet, PEG feeding if unsafe swallow, oral hygiene, aspiration precautions (upright positioning during and after feeds) |
| Aspect | Detail |
|---|---|
| Mechanism | Combined restrictive defect + respiratory muscle weakness + impaired cough (weak expiratory muscles → ineffective airway clearance) → hypoventilation → type 2 respiratory failure |
| Management | NIV (BiPAP) for nocturnal hypoventilation; chest physiotherapy; cough-assist devices; influenza and pneumococcal vaccination |
| Significance | Respiratory failure is the second most common cause of death after cardiac causes, especially in patients with severe scoliosis |
These are often underappreciated but contribute significantly to morbidity.
| Complication | Mechanism | Prevention |
|---|---|---|
| Pressure ulcers | Sustained pressure on bony prominences (sacrum, ischial tuberosities, heels) in wheelchair-bound patients → tissue ischaemia → necrosis | Pressure-relieving wheelchair cushions, regular repositioning (every 2 hours), skin inspection, nutrition optimisation |
| Deep vein thrombosis (DVT) | Immobility → venous stasis → thrombosis (Virchow's triad: stasis, endothelial damage, hypercoagulability) | Passive limb exercises, compression stockings, adequate hydration. Prophylactic anticoagulation if hospitalised |
| Osteoporosis | Reduced weight-bearing → decreased bone loading → ↓ osteoblast activity → bone loss. Also vitamin D deficiency (reduced sun exposure), possible endocrine contributions | Weight-bearing exercises where possible, vitamin D + calcium supplementation, bone density monitoring (DXA scan) |
| Constipation | Immobility + reduced physical activity + possible autonomic involvement + medication side effects (anticholinergics) → slowed gut transit | Dietary fibre, adequate fluids, regular toileting, laxatives if needed |
| Joint contractures | Prolonged immobility → muscle shortening → fixed joint deformity (especially ankles, knees, hips) | Regular stretching programme (PT-supervised), splinting, standing frames |
| Urinary tract infections | Incomplete bladder emptying (neurogenic bladder) + catheterisation | Bladder management programme, avoid unnecessary catheterisation, adequate hydration |
8. Psychosocial Complications
These are arguably the most impactful on quality of life, especially in the paediatric population.
| Aspect | Detail |
|---|---|
| Frequency | Depression affects ~20–40% of FRDA patients; anxiety is also common |
| Mechanism | Psychological reaction to chronic progressive disability (loss of independence, body image changes, social isolation, anticipatory grief about the future). Note: FRDA itself does NOT cause cognitive decline, so the child is fully aware of their deterioration |
| Impact in adolescents | Identity formation disrupted; peer relationships affected; school participation limited; romantic and sexual development complicated by disability |
| Management | Regular mental health screening; CBT (cognitive-behavioural therapy); SSRIs if pharmacotherapy needed (fluoxetine licensed from age 8 in paediatrics); peer support groups; family therapy |
| Aspect | Detail |
|---|---|
| Mechanism | Dysarthria → communication difficulty; wheelchair dependence → access barriers; fatigue → reduced participation |
| Mitigation | School accommodations, inclusive extracurricular activities, technology-assisted communication, online communities |
| Aspect | Detail |
|---|---|
| Parents | Grief (diagnosis of incurable progressive disease in their child); guilt (carrier status — "I passed this on"); caregiver burden (progressive physical dependence); financial strain (equipment, adaptations, reduced work capacity); marital stress |
| Siblings | May feel neglected (attention focused on affected child); may feel guilt (if unaffected); anxiety about own carrier status; may become young carers |
| Management | Family-centred care model; respite care; sibling support programmes; genetic counselling addressing guilt and reproductive options; social work involvement for practical support |
| Aspect | Detail |
|---|---|
| Cognitive function | Typically preserved — this is crucial. FRDA children have NORMAL intelligence and should be supported to achieve their full academic potential |
| Barriers | Physical access (wheelchair), writing difficulty (limb ataxia), speech difficulty (dysarthria), fatigue, frequent medical appointments |
| Accommodations | Extra time in exams, scribe or voice-to-text technology, wheelchair-accessible facilities, modified PE curriculum, flexibility for medical appointments |
9. Treatment-Related Complications
| Complication | Detail |
|---|---|
| Hepatotoxicity | Elevated ALT/AST — dose-dependent; monitor LFTs monthly then quarterly. Discontinue if > 5× ULN |
| Elevated BNP | May indicate fluid retention; assess for clinical heart failure |
| Weight loss | Appetite suppression — particularly concerning in growing adolescents; monitor weight and nutritional status |
| Drug interactions | CYP3A4 metabolism — concomitant inhibitors (ketoconazole, macrolides) increase toxicity; inducers (anti-epileptics) reduce efficacy |
| Surgery | Complications |
|---|---|
| Spinal fusion for scoliosis | Anaesthetic risk (cardiomyopathy, restrictive lung disease); wound infection; hardware failure; blood loss; neurological injury (rare); prolonged recovery in a patient with limited mobility reserve |
| Cardiac surgery / transplant | Standard surgical risks; immunosuppression complications; ongoing neurological progression despite cardiac improvement |
| PEG insertion | Insertion-site infection, tube migration, aspiration during procedure |
Anaesthetic Risk in FRDA — Critical for Exams
Children with FRDA undergoing any surgery carry increased anaesthetic risk due to:
- Cardiomyopathy (arrhythmia risk under general anaesthesia, sensitivity to negative inotropes)
- Restrictive lung disease (difficult ventilation, slower post-operative respiratory recovery)
- Autonomic dysfunction (exaggerated hypotensive response to induction agents)
- Scoliosis (difficult intubation positioning, reduced chest wall compliance)
Always request pre-operative cardiac assessment (echo + ECG) and involve the paediatric anaesthesia team early.
| Time from Onset | Expected Complications |
|---|---|
| 0–5 years | Progressive gait ataxia, pes cavus, scoliosis (early), ECG changes (T-wave inversions), subclinical HCM on echo |
| 5–10 years | Significant gait deterioration (may need walking aids), worsening dysarthria, progressive scoliosis (especially during pubertal growth spurt), impaired glucose tolerance |
| 10–15 years | Wheelchair dependence, overt HCM (may be symptomatic), possible diabetes onset, dysphagia beginning |
| 15–25 years | Severe dysarthria (may need AAC), significant dysphagia (may need PEG), respiratory compromise (NIV), arrhythmias, possible transition from HCM to DCM |
| 25+ years | Heart failure, respiratory failure, aspiration pneumonia — the common terminal events |
| System | Investigation | Frequency | Purpose |
|---|---|---|---|
| Cardiac | ECG + Echo + Holter | Annual | Detect progression from HCM → DCM, arrhythmias |
| Endocrine | Fasting glucose + HbA1c ± OGTT | Annual | Detect pre-diabetes/diabetes early |
| Skeletal | Spine examination ± X-ray (Cobb angle) | Every 6–12 months (more frequent during pubertal growth spurt) | Detect progressive scoliosis requiring intervention |
| Respiratory | Spirometry (FVC) + nocturnal oximetry | Annual (from when cooperation allows, ~age 6) | Detect restrictive decline, hypoventilation |
| Neurological | Functional assessment (mFARS/SARA scale) | Every 6–12 months | Track progression, guide rehabilitation goals |
| Ophthalmology | Visual acuity + fundoscopy ± OCT | Annual | Detect optic atrophy |
| Audiology | Pure tone audiometry | Annual | Detect hearing loss |
| Swallowing | Clinical assessment ± VFSS/FEES | As clinically indicated (at least annually from late disease) | Detect unsafe swallow → prevent aspiration |
| Mental health | Depression/anxiety screening (e.g., PHQ-A in adolescents) | Every clinic visit | Early intervention for psychological complications |
| Bone health | Vitamin D level; DXA scan if concerns | Annually (vitamin D); DXA as indicated | Prevent osteoporotic fractures |
High Yield Summary — Complications of Friedreich Ataxia
- Cardiomyopathy (HCM → DCM) is the #1 cause of death (~60% of deaths) [14] — sudden cardiac death from arrhythmias can occur at any age
- Respiratory failure is the #2 cause of death — from restrictive lung disease (scoliosis + respiratory muscle weakness) + aspiration pneumonia (dysphagia)
- Diabetes mellitus affects 10–30% — mixed insulin deficiency + insulin resistance; diabetic complications superimpose on FRDA neuropathy and cardiomyopathy ("double hit")
- Progressive loss of ambulation within 10–15 years → wheelchair dependence → complications of immobility (pressure ulcers, DVT, osteoporosis, contractures, constipation)
- Scoliosis (60–80%) — accelerates during pubertal growth spurt; severe scoliosis → restrictive lung disease
- Dysarthria → dysphagia → aspiration is a progressive sequence leading to pneumonia, malnutrition, and ultimately PEG dependence
- Cognition is preserved — the child is intellectually aware of their progressive decline → depression and anxiety are common (~20–40%)
- Family impact is enormous (parental guilt, caregiver burden, sibling effects) — family-centred care and genetic counselling are essential
- Anaesthetic risk is increased — cardiomyopathy, restrictive lung disease, autonomic dysfunction, scoliosis all complicate surgical procedures
- Annual multi-system surveillance is mandatory — early detection of complications allows timely intervention
Active Recall — Complications of Friedreich Ataxia
[14] Senior notes: Adrian Lui Pediatrics Notes.pdf (p129 — Hereditary Ataxia: Friedreich's ataxia — cardiomyopathy most common cause of death; Mx: supportive) [15] Senior notes: Ryan Ho Endocrine.pdf (p94 — Chronic diabetic complications: microvascular retinopathy/nephropathy/neuropathy; macrovascular IHD/PVD/CVD) [16] Senior notes: Block A - Polyuria and polydipsia_ glucose metabolism; diabetes mellitus; diabetic ketoacidosis.pdf (p20 — Screening for chronic complications: for pre-pubertal patients, screen annually after 5 years of diabetes)
High Yield Summary
Friedreich Ataxia — Key Points for Exams:
- Most common hereditary ataxia; autosomal recessive inheritance
- GAA trinucleotide repeat expansion in intron 1 (non-coding) of FXN gene (chromosome 9q21) → ↓ frataxin
- Non-coding repeat → decreased protein production (not toxic protein accumulation)
- Frataxin deficiency → impaired Fe-S cluster assembly → mitochondrial iron accumulation → oxidative stress → cell death
- Onset typically age 5–15 years with progressive gait ataxia
- Pathognomonic sign combination: areflexia + extensor plantars (upgoing Babinski) — concurrent LMN (DRG) + UMN (corticospinal) degeneration
- Key affected structures: dorsal root ganglia, posterior columns, spinocerebellar tracts, corticospinal tracts, dentate nucleus, cardiomyocytes, pancreatic β-cells
- Cardinal features: progressive ataxia (sensory + cerebellar), dysarthria, pes cavus, scoliosis, hypertrophic cardiomyopathy, diabetes mellitus
- Leading cause of death: cardiomyopathy (cardiac failure/arrhythmia)
- Larger GAA repeat size → earlier onset, more severe disease (anticipation principle)
- Cognition typically preserved — distinguish from other neurodegenerative disorders
- Listed alongside Fragile X syndrome (CGG), Myotonic dystrophy (CTG), Huntington disease (CAG), and Spinocerebellar ataxia (CAG) as key trinucleotide repeat disorders
High Yield Summary — Differential Diagnosis of Friedreich Ataxia
- FRDA is the most common hereditary ataxia — but always exclude treatable mimics first (AVED, Wilson, Refsum, abetalipoproteinaemia, B12 deficiency, tumour)
- The pathognomonic triad (areflexia + upgoing plantars + progressive ataxia) distinguishes FRDA from most differentials
- Ataxia-telangiectasia is the main AR childhood ataxia differential — distinguished by telangiectasias, immunodeficiency, ↑AFP, cancer risk
- Spinocerebellar ataxias (AD) are more common than FRDA in East Asian / Hong Kong Chinese populations — adult onset, brisk reflexes, AD inheritance
- AVED is a clinical phenocopy of FRDA that is treatable with vitamin E — always check serum vitamin E
- Wilson disease must be excluded in any child with progressive ataxia — slit-lamp exam, caeruloplasmin, urine copper
- SMA (AR, motor-only) and CMT (peripheral neuropathy only) lack cerebellar and sensory features of FRDA
- Non-progressive ataxia → think cerebral palsy; acute onset → think post-infectious or tumour
High Yield Summary — Diagnosis of Friedreich Ataxia
- Diagnosis is confirmed by genetic testing — GAA trinucleotide repeat expansion in FXN gene (chromosome 9q21), ≥ 66 repeats on both alleles (homozygous, 96%) or one expanded allele + point mutation (compound heterozygote, 4%)
- Harding essential criteria (clinical suspicion): AR inheritance, onset before 25 years, progressive ataxia, absent knee and ankle jerks, axonal sensory neuropathy on NCS
- NCS shows axonal sensory neuropathy: absent or severely reduced SNAPs with normal motor conduction — an essential diagnostic criterion
- ECG abnormalities (T-wave inversions, LVH) are often the earliest cardiac sign — do NOT dismiss in a child with ataxia
- Echocardiography shows concentric LVH using paediatric z-scores (not adult cutoffs)
- MRI brain is often normal early (unlike SCAs); MRI spinal cord shows cervical cord atrophy
- Always exclude treatable mimics first: serum vitamin E (AVED), caeruloplasmin/slit-lamp (Wilson), B12
- The smaller GAA allele (GAA1) best predicts age of onset and severity
- Larger GAA repeat size → earlier onset, more severe disease, more cardiomyopathy [13]
- Multi-system annual surveillance (cardiac, endocrine, skeletal, respiratory, ophthalmology, audiology) is mandatory after diagnosis
High Yield Summary — Management of Friedreich Ataxia
- Management has traditionally been supportive [14] — but omaveloxolone (Nrf2 activator) is now the first FDA-approved disease-modifying therapy (approved ≥ 16 years, 150 mg daily oral)
- Omaveloxolone slows neurological decline but does NOT cure or reverse existing damage; monitor LFTs monthly then quarterly
- Cardiac management is the most critical aspect — cardiomyopathy is the leading cause of death. ACE-I/ARB for HCM; standard HF therapy if DCM develops; ICD for high-risk arrhythmias
- FRDA diabetes is a mixed picture (β-cell destruction + insulin resistance) — may need insulin early (unlike typical T2DM)
- Rehabilitation (PT, OT, speech therapy) is the backbone of care at ALL stages — exercise is beneficial, not harmful
- Scoliosis must be monitored aggressively during pubertal growth spurt — brace if 20–40°, surgical fusion if > 40–50° or rapidly progressive
- Iron chelation is NOT standard of care — total body iron is normal; only mitochondrial iron is misdistributed
- Genetic counselling is essential: AR, 25% recurrence risk, prenatal diagnosis and PGT available
- Family-centred care with psychological support, school liaison, and transition planning from age 12–14 years
High Yield Summary — Complications of Friedreich Ataxia
- Cardiomyopathy (HCM → DCM) is the #1 cause of death (~60% of deaths) [14] — sudden cardiac death from arrhythmias can occur at any age
- Respiratory failure is the #2 cause of death — from restrictive lung disease (scoliosis + respiratory muscle weakness) + aspiration pneumonia (dysphagia)
- Diabetes mellitus affects 10–30% — mixed insulin deficiency + insulin resistance; diabetic complications superimpose on FRDA neuropathy and cardiomyopathy ("double hit")
- Progressive loss of ambulation within 10–15 years → wheelchair dependence → complications of immobility (pressure ulcers, DVT, osteoporosis, contractures, constipation)
- Scoliosis (60–80%) — accelerates during pubertal growth spurt; severe scoliosis → restrictive lung disease
- Dysarthria → dysphagia → aspiration is a progressive sequence leading to pneumonia, malnutrition, and ultimately PEG dependence
- Cognition is preserved — the child is intellectually aware of their progressive decline → depression and anxiety are common (~20–40%)
- Family impact is enormous (parental guilt, caregiver burden, sibling effects) — family-centred care and genetic counselling are essential
- Anaesthetic risk is increased — cardiomyopathy, restrictive lung disease, autonomic dysfunction, scoliosis all complicate surgical procedures
- Annual multi-system surveillance is mandatory — early detection of complications allows timely intervention
Fragile X Syndrome
Fragile X syndrome is an X-linked trinucleotide repeat expansion disorder in the FMR1 gene, representing the most common inherited cause of intellectual disability and autism spectrum features in children, particularly boys, typically presenting in early childhood with developmental delay, characteristic facial features, and behavioral difficulties.
Huntington Disease
Huntington disease is an autosomal dominant neurodegenerative disorder caused by a CAG trinucleotide repeat expansion in the HTT gene, with the rare juvenile form (onset before age 20) typically presenting with rigidity, cognitive decline, and seizures rather than the classic adult chorea.