Alport syndrome is a hereditary nephropathy caused by mutations in type IV collagen genes, characterized by progressive glomerulonephritis, sensorineural hearing loss, and ocular abnormalities.

Exam domain	One-glance essentials
Definition / diagnosis	Inherited COL4A3/COL4A4/COL4A5 type IV collagen disorder affecting GBM, cochlea and eye ^[1]^[2] Most cases are X-linked COL4A5; autosomal recessive/dominant forms involve COL4A3/4 ^[2]
Epidemiology / risks	*No father-to-son transmission in X-linked disease* ^[1] Male X-linked and autosomal-recessive disease usually progress earlier; females may still develop CKD ^[2]
Core mechanism	Defective α3α4α5 collagen network → fragile GBM → splitting/lamellation → glomerulosclerosis and CKD ^[2] The same collagen network defect causes high-frequency SNHL and ocular lesions ^[1]^[2]
Clinical picture	Persistent haematuria from childhood → proteinuria, hypertension and progressive renal impairment ^[2] High-tone sensorineural deafness + anterior lenticonus/retinal flecks are key extrarenal clues ^[1]^[2]
Investigations	Genetic testing for COL4A3/4/5 establishes subtype and inheritance ^[2] EM: alternating thinning/thickening and lamina-densa splitting (basket weave); standard IF is negative ^[2] PTA, ophthalmic examination and cascade family urinalysis/genetics ^[1]^[2]
Management	Start ACEI/ARB when albuminuria/proteinuria emerges to slow progression ^[2] Avoid nephrotoxins; manage CKD, hearing and visual needs; transplant is preferred for ESKD ^[2] Provide genetic counselling and assess relatives before living donation ^[2]
Complications	Progressive CKD/ESKD, hearing disability and ocular disease ^[2] A minority develop de novo anti-GBM disease after transplantation ^[2]
Prevention / follow-up	Cascade screening, genetic counselling and early RAAS blockade reduce avoidable family morbidity ^[2] Annual BP, urine protein, eGFR and hearing follow-up; exclude carriers from unsafe kidney donation ^[2]
Exam traps	*Almost all female X-linked carriers have haematuria; some develop renal failure through lyonisation* ^[1] TBMD lacks progressive CKD, deafness/ocular signs and basket-weave GBM in the typical low-risk phenotype ^[2] Anterior lenticonus is a highly specific clue ^[2]

References

^[1] Lecture slides: GC 057. Glomerular and Tubulo-interstitial Diseases and Acute Kidney Injury.pdf (p18 — Alport inheritance and clinical differentiation) ^[2] Senior notes: Ryan Ho Urogenital.pdf (p60–61 — Alport syndrome diagnosis, inheritance, complications and management)

Alport Syndrome (Hereditary Nephritis)

Alport syndrome is an inherited disorder of type IV collagen that primarily affects the glomerular basement membrane (GBM), the cochlea, and the eye. The name tells you what it is: "Alport" = after Cecil Alport, the South African physician who first described the association of hereditary nephritis with deafness in 1927; "syndrome" = a constellation of features occurring together.

At its core, this is a basement membrane disease. Type IV collagen is the structural scaffold of basement membranes throughout the body, but the GBM, cochlea (organ of Corti), and lens capsule are particularly dependent on the α3-α4-α5 type IV collagen network — which is precisely what is defective in Alport syndrome ^[1]^[2].

Key Concept

Alport syndrome = inherited mutation in type IV collagen genes (COL4A3, COL4A4, or COL4A5) → defective α3-α4-α5 collagen IV network → progressive glomerular disease + sensorineural hearing loss ± ocular abnormalities.

Prevalence: approximately 1 in 5,000 live births ^[2]
Accounts for 0.3–2.3% of new cases of ESRD (end-stage renal disease) ^[2]
One of the most common inherited causes of kidney failure — often underdiagnosed because early disease presents only as "asymptomatic haematuria"
Males with X-linked Alport syndrome are more severely affected; median age of ESRD is 16–35 years for X-linked and autosomal recessive forms ^[2]
In Hong Kong and East Asia, Alport syndrome is an important cause of familial haematuria and should always be considered when a young patient (especially male) presents with persistent glomerular haematuria + family history of renal failure or deafness

Since this is a genetic disease, "risk factors" really means genetic risk:

Family history of renal failure, deafness, or haematuria — the single most important risk factor
Male sex (for X-linked form): males are hemizygous (only one X chromosome), so a single mutant copy of COL4A5 = full-blown disease
Specific genotype: truncating mutations (nonsense, frameshift, large deletions) in COL4A5 tend to cause earlier ESRD than missense mutations
Proteinuria > 1 g/day and hearing loss before age 30 are clinical predictors of faster progression to ESRD

Anatomy & Function: Type IV Collagen and the GBM

The GBM is a specialized extracellular matrix lying between the glomerular endothelium and the podocytes. It has three layers:

Lamina rara interna (endothelial side)
Lamina densa (central dense layer — the main filtration barrier)
Lamina rara externa (podocyte side)

The GBM's structural integrity depends on a network of type IV collagen, which forms a mesh-like scaffold.

Type IV collagen has six α-chains (α1 through α6), encoded by genes COL4A1 through COL4A6. These chains assemble into triple-helix trimers (protomers) that then cross-link into a network:

Network	Chains	Where found	Role
α1-α1-α2	COL4A1 + COL4A2	Ubiquitous (all basement membranes); also the embryonic/fetal GBM	Basic structural scaffold
α3-α4-α5	COL4A3 + COL4A4 + COL4A5	Mature GBM, cochlear basement membrane, lens capsule, retina	Replaces the embryonic network; provides mechanical strength and resistance to proteolysis
α5-α5-α6	COL4A5 + COL4A6	Bowman's capsule, skin, smooth muscle	Tissue-specific functions

Why does Alport syndrome target the kidney, ear, and eye? Because the α3-α4-α5 network is specifically expressed in the GBM, the basement membrane of the cochlea (supporting the organ of Corti), and the lens capsule/retina. Other basement membranes (e.g., skin, gut) use the ubiquitous α1-α1-α2 network and are therefore spared.

The organ of Corti is the sensory organ of hearing, sitting on the basilar membrane in the cochlea. The basement membrane connecting the organ of Corti to the basilar membrane contains the α3-α4-α5 collagen IV network. Defective collagen → ↓ adhesion of the organ of Corti to the basilar membrane → progressive sensorineural hearing loss, beginning in the high-frequency range ^[1]^[2].

The lens capsule (the thickest basement membrane in the body) and retinal basement membranes also express α3-α4-α5 collagen IV. Defects here cause anterior lenticonus (forward protrusion of the lens), perimacular retinal flecks, and other ocular pathology.

Aetiology & Genetics

Alport syndrome is caused by inherited mutations in the type IV collagen genes ^[1]^[2]:

Pattern	Frequency	Gene(s)	Key Points
X-linked (XL)	~80%	COL4A5 (Xq22.3)	Most common form. Father-to-son transmission does not occur (father passes Y to son). Males = full-blown disease; females = heterozygous carriers with variable expression ^[1]
Autosomal recessive (AR)	~15%	COL4A3 or COL4A4 (chromosome 2q36)	Both alleles must be mutated. Males and females equally affected. Similar severity to XL males.
Autosomal dominant (AD)	< 5%	Heterozygous COL4A3 or COL4A4	Associated with slower disease progression (ESRD typically > 45 years). Some develop thin basement membrane disease instead (reason unknown) ^[2]

X-linked Inheritance — Key Exam Points

Father-to-son transmission does not occur in X-linked Alport — because fathers pass the Y chromosome to sons ^[1].
An affected father passes the mutant X to all daughters → they become carriers.
Women with X-linked Alport syndrome are heterozygous carriers. Almost all have some degree of haematuria, and some develop renal failure due to lyonization (random X-inactivation) ^[1].
Lyonization = in each cell, one X chromosome is randomly inactivated. If the normal X is preferentially inactivated in a carrier female's kidneys, she may express significant disease.

The type of mutation in COL4A5 predicts severity in X-linked Alport:

Truncating mutations (nonsense, frameshift, splice-site, large deletions): → complete absence of α5 chain → no α3-α4-α5 network assembled → severe disease, ESRD by ~20 years
Missense mutations: → structurally abnormal but partially functional α5 chain → milder disease, ESRD at ~30 years or later
Splice-site mutations: variable severity

Pathophysiology

This is best understood as a stepwise process from gene to disease:

Collagen IV malformation: COL4A3-5 encodes the 3 α-chains that form α3-4-5 collagen IV fibres in GBM ^[2]
Glomerular injury: malformation of α3-4-5 network → persistence of embryonic α1-1-2 network ^[2]
- Why does the embryonic network persist? During normal kidney development, the GBM transitions from the fetal α1-α1-α2 network to the mature α3-α4-α5 network (a process called the "collagen IV switch"). In Alport syndrome, the α3-α4-α5 network cannot be made, so the fetal α1-α1-α2 network persists by default.
↑ susceptibility to endoproteolysis and oxidative stress → GBM splitting and damage ^[2]
- The α1-α1-α2 network lacks the extensive disulfide cross-links that make the α3-α4-α5 network resistant to proteases. It is essentially a "weaker" scaffold.
Progressive CKD: GBM damage → secondary glomerulosclerosis (GS) + tubulointerstitial fibrosis (TIF) → proteinuria and progressive CKD ^[2]
- As the GBM deteriorates, podocytes are injured (foot process effacement), mesangial expansion occurs, and the typical scarring cascade follows.

Defective α-3-4-5 type IV collagen → ↓ adhesion of the Organ of Corti (the auditory sensory cells) to the basilar membrane → high-tone deafness ^[1]
This is a structural problem: the organ of Corti literally loses its mechanical coupling to the basilar membrane, impairing sound transduction starting with high frequencies (because the basal turn of the cochlea, responsible for high frequencies, is most vulnerable).

Defective α3-α4-α5 collagen in the lens capsule → anterior lenticonus (the lens bulges forward because its capsule is weak)
Defective collagen in retinal basement membranes → perimacular flecks (dot-and-fleck retinopathy)

Classification

Type	Gene	Inheritance	Severity
Type 1 (X-linked)	COL4A5	X-linked	Severe in males; variable in carrier females
Type 2 (Autosomal recessive)	COL4A3 or COL4A4	AR	Severe, similar to XL males
Type 3 (Autosomal dominant)	COL4A3 or COL4A4 (heterozygous)	AD	Milder; may overlap with thin basement membrane disease

Classic Alport syndrome: haematuria + progressive CKD + sensorineural hearing loss ± ocular features
Alport syndrome without hearing loss: some patients (especially with milder missense mutations) may not develop hearing loss
Alport syndrome with leiomyomatosis: rare variant (contiguous gene deletion involving COL4A5 and COL4A6 on Xq22) → diffuse leiomyomatosis of the oesophagus, tracheobronchial tree, and female genital tract

Clinical Features

A. Symptoms (with pathophysiological basis)

Symptom	Pathophysiological Basis
Asymptomatic persistent haematuria, usually in early childhood (< 10 years) ^[2]	Defective GBM → RBCs leak through the damaged basement membrane. Haematuria is glomerular in origin: smoky/cola-coloured, dysmorphic RBCs, no clots (urokinase in glomerular filtrate lyses clots) ^[3]
Episodic gross (macroscopic) haematuria — often triggered by URTIs	Intercurrent infections cause transient haemodynamic and inflammatory stress on the already-damaged GBM, transiently worsening RBC leakage
Later develop proteinuria (< 1–2 g/day) ^[2]	Progressive podocyte injury secondary to GBM damage → loss of slit-diaphragm integrity → protein leakage. Proteinuria is usually subnephrotic (< 3.5 g/day)
Oedema (rare, late)	If proteinuria becomes nephrotic range (uncommon), hypoalbuminaemia → reduced oncotic pressure → oedema
Symptoms of CKD (fatigue, nausea, anorexia, pruritus) — late	Progressive CKD: GBM damage → secondary glomerulosclerosis + tubulointerstitial fibrosis → declining GFR → uraemic symptoms ^[2]

Symptom	Pathophysiological Basis
Bilateral sensorineural hearing loss, beginning in high-frequency range and progressing to affect lower frequencies ^[2]	↓ adhesion of Organ of Corti to basilar membrane via defective α-3-4-5 collagen IV ^[1]^[2]. High frequencies are affected first because the basal cochlear turn (high-frequency zone) has the highest mechanical demands
Difficulty hearing conversations in noisy environments (early)	High-frequency hearing loss impairs speech discrimination, especially against background noise
Not present at birth — develops progressively in late childhood/adolescence	The cochlear basement membrane undergoes cumulative mechanical stress; the fetal α1-α1-α2 network gradually fails under ongoing acoustic vibration

Key point: Hearing deficit is common → pure-tone audiometry (PTA) is the investigation ^[1]. In any young patient with haematuria, ALWAYS ask about hearing and arrange PTA.

Symptom	Pathophysiological Basis
Progressive visual deterioration (if anterior lenticonus is present)	Anterior lenticonus = forward bulging of the lens due to weak capsule (defective collagen IV) → irregular refraction → progressive myopia and astigmatism
Visual disturbance from retinal flecks (usually asymptomatic)	Perimacular dot-and-fleck retinopathy — deposits in the retina around the macula; usually does not significantly impair vision

B. Signs (with pathophysiological basis)

Sign	Pathophysiological Basis
Urinalysis: haematuria (microscopic or macroscopic)	GBM defect → glomerular RBC leak
Dysmorphic RBCs and RBC casts on urine microscopy	RBCs are distorted as they squeeze through the damaged GBM and conform to tubular shape
Hypertension (develops in adolescence/early adulthood)	Progressive glomerulosclerosis → sodium retention + RAAS activation → hypertension
Oedema (late)	Significant proteinuria → hypoalbuminaemia
Signs of uraemia (late): asterixis, pericardial rub, uraemic frost	End-stage renal failure → accumulation of uraemic toxins

Sign	Pathophysiological Basis
Sensorineural hearing loss on PTA — initially high-frequency (2000–8000 Hz), later involving lower frequencies ^[2]	Structural failure of cochlear basement membrane
Weber test: lateralizes to the better ear (or midline if bilateral)	Sensorineural loss = inner ear problem → sound not conducted more efficiently via bone
Rinne test: air conduction > bone conduction bilaterally (positive Rinne) — but both are reduced	Sensorineural loss preserves the AC > BC relationship but at lower absolute levels

Sign	Pathophysiological Basis
Anterior lenticonus (pathognomonic for Alport syndrome) ^[2]	Forward bulging of the central portion of the lens due to thinning and weakness of the anterior lens capsule (defective collagen IV). Seen on slit-lamp exam as an "oil droplet" reflex on retroillumination
Perimacular retinal flecks (dot-and-fleck retinopathy) ^[2]	Yellow-white deposits around the macula on fundoscopy — due to abnormal Bruch's membrane (which also contains type IV collagen)
Posterior polymorphous corneal dystrophy ^[2]	Defective collagen IV in Descemet's membrane (corneal basement membrane) → corneal endothelial vesicular lesions
Recurrent corneal erosion ^[4]	Defective adhesion of corneal epithelium to its basement membrane

Sign	Pathophysiological Basis
Leiomyomatosis (2–5%) ^[2]	Contiguous deletion of COL4A5 and COL4A6 → abnormal smooth muscle basement membranes → benign smooth muscle tumours of the oesophagus, tracheobronchial tree, or female genital tract
Thoracic/abdominal aortic aneurysms ^[2]	Rare; defective collagen IV in the vascular basement membrane → structural weakness of the aortic wall

Clinical Pearl: Anterior Lenticonus

Anterior lenticonus is virtually pathognomonic for Alport syndrome. If you see this on slit-lamp examination in a patient with haematuria, the diagnosis is essentially confirmed. No other common condition causes anterior lenticonus.

Histopathology

Non-specific ^[2] in early disease
Later characterised by focal ↑ cellularity, glomerulosclerosis (GS), tubulointerstitial fibrosis (TIF) ^[2]
May see foam cells (lipid-laden interstitial cells) — a relatively characteristic but not pathognomonic finding

EM shows: thinning (earliest change), splitting of lamina densa (laminated), alternate thinning/thickening (basket-weave appearance) ^[2]
The "basket-weave" pattern is the hallmark EM finding: the GBM shows irregular thickening with splitting of the lamina densa into multiple interlacing layers, with electron-dense granular deposits within the splits

Why does the GBM look like a basket-weave? The defective α1-α1-α2 network that persists in place of the normal α3-α4-α5 network is mechanically unstable. Under ongoing filtration pressure, it undergoes cycles of damage, attempted repair, and re-damage → layered splitting and irregular thickening.

Severity of histologic changes increases with age ^[2]
- Children may show only thinning of the GBM (may be confused with thin basement membrane disease)
- Adolescents/adults show the classic basket-weave pattern

Should be negative on standard IF (no immune complex deposition — this is NOT an immune-mediated disease) ^[2]
Negative for α3, α4, α5 chain immunostains if special collagen IV chain-specific antibodies are used ^[2]
- In X-linked Alport males: absent staining for α3, α4, and α5 in GBM (all three chains are needed to form the heterotrimer; if α5 is absent, α3 and α4 cannot be incorporated)
- In carrier females: mosaic pattern (some segments of GBM stain, others do not — reflecting lyonization)

Histology Summary — High Yield for Exams

Feature	Finding
LM	Non-specific early; later GS + TIF + foam cells
EM	Basket-weave appearance — alternating thinning and thickening with lamina densa splitting
IF	Negative (no immune deposits); absent α3-α4-α5 staining with specific antibodies

This is a classic exam question ^[1]^[4]:

How can the three glomerular causes of haematuria be distinguished? ^[1]

Feature	IgA Nephropathy	Alport Syndrome	Thin Basement Membrane Disease (TBMD)
Gross haematuria	Common	Common	Unusual (< 10%) ^[1]
Timing	Synpharyngitic (concurrent with URTI)	Persistent from childhood	Persistent, often detected incidentally
Family history	May run in families but no particular mode of inheritance, no one gene ^[1]	Renal failure / deafness primarily in males, X-linked dominant mode of inheritance ^[1]	Runs in families ^[1]; 30–50% have FHx of haematuria; generally benign course ^[4]
Inheritance	Non-Mendelian	X-linked (80%), AR, AD	AD
Hearing loss	No	Yes (SNHL)	No
Ocular features	No	Yes (anterior lenticonus, retinal flecks)	No
Prognosis	Variable (20–40% progress to ESRD over 20 years)	Progressive → ESRD	Benign (usually no CKD)
EM	Mesangial deposits	Basket-weave GBM	Thin GBM (diffusely < 250 nm; best visualised by electron microscopy ^[1])
IF	Mesangial IgA	Negative	Negative

Key evaluation approach: History + urinalysis of family members ^[1]

Exam Tip

Do NOT confuse thin basement membrane disease with early Alport syndrome. In young children, the GBM in Alport may be thin (before the basket-weave develops), and this can mimic TBMD on EM. The key differentiators are: (1) family history pattern, (2) hearing loss, (3) genetic testing for COL4A mutations, and (4) serial follow-up — Alport progresses while TBMD does not.

ESRD usually occurs at 16–35 years old (for X-linked and AR cases) ^[2]
AD Alport: ESRD typically > 45 years ^[2]

High Yield Summary

Alport Syndrome — Key Points for Exams:

Definition: Inherited type IV collagen disorder (COL4A3/A4/A5) → defective α3-α4-α5 collagen IV network in GBM, cochlea, eye
Inheritance: X-linked 80% (COL4A5), AR 15% (COL4A3/A4), AD < 5%
No father-to-son transmission in X-linked form
Female carriers (X-linked): almost all have haematuria, some develop renal failure (lyonization)
Pathogenesis: Absent α3-4-5 network → persistence of embryonic α1-1-2 network → susceptible to proteolysis → GBM splitting → basket-weave on EM → GS + TIF → CKD → ESRD
Clinical triad: Haematuria/CKD + SNHL (high-tone first) + ocular abnormalities (anterior lenticonus = pathognomonic)
EM: Basket-weave GBM (alternating thinning/thickening, lamina densa splitting)
IF: Negative (NOT immune-mediated)
PTA: Investigation of choice for hearing loss
Distinguished from TBMD: TBMD is AD, benign course, thin GBM, no hearing/eye involvement; Alport progresses to ESRD
ESRD age: 16–35y (XL males, AR); > 45y (AD)

Active Recall - Alport Syndrome

Differential Diagnosis of Alport Syndrome

When a patient presents with the core features of Alport syndrome — persistent glomerular haematuria, sensorineural hearing loss (SNHL), ocular abnormalities, and/or a family history of renal failure — the clinician must systematically consider alternative diagnoses that can mimic one or more of these features. The differential diagnosis should be approached from two angles:

What else presents as isolated/persistent glomerular haematuria? (the most common initial presentation)
What else presents as a combined renal + deafness syndrome? (the more specific presentation)

We also need to consider mimics of the progressive CKD component and conditions that share histological features.

This is the classic "three causes of isolated glomerular haematuria" framework, which is extremely high-yield ^[1]^[2]^[4]:

The three classic causes of isolated glomerular haematuria are: (1) IgA nephropathy, (2) Alport syndrome, and (3) thin basement membrane disease (TBMD) ^[1]^[4]

Feature	IgA Nephropathy	Alport Syndrome	Thin Basement Membrane Disease
Age of onset	Usually adult (20–30y)	Childhood (< 10 years) ^[2]	Childhood (often detected incidentally)
Gross haematuria	Common — classically synpharyngitic (concurrent with URTI) ^[4]	Common — may be triggered by intercurrent illness	Unusual (< 10%) ^[1]
Pattern of haematuria	Episodic macroscopic on background of microscopic	Persistent microscopic with occasional macroscopic	Persistent microscopic; rarely macroscopic
Proteinuria	Variable; can become nephrotic	< 1–2 g/day, develops later ^[2]	Usually minimal (< 0.5 g/day)
Family history	Runs in families but no particular mode of inheritance, no one gene ^[1]	Renal failure / deafness primarily in males, X-linked dominant mode of inheritance ^[1]	Runs in families — AD; 30–50% FHx of haematuria; generally benign course ^[4]
SNHL	No	Yes — bilateral, high-frequency first	No
Ocular features	No	Yes — anterior lenticonus (pathognomonic), retinal flecks	No
Prognosis	Variable (20–40% → ESRD over 20y)	Progressive → ESRD (16–35y for XL/AR)	Benign — vast majority never develop CKD
EM	Mesangial electron-dense deposits	Basket-weave GBM (splitting of lamina densa) ^[2]	Thin GBM (diffusely < 250 nm; best visualised by electron microscopy ^[1])
IF	Mesangial IgA deposits	Negative ^[2]; absent α3-α4-α5 staining	Negative
Serology	Elevated serum IgA in ~50%	No specific serological marker	No specific serological marker

Key Distinguishing Approach

History + urinalysis of family members is the first-line approach to distinguish these three conditions ^[1]. Ask about:

Family history of renal failure and deafness (→ Alport)
Family history of haematuria without progression (→ TBMD)
No clear Mendelian pattern (→ IgA nephropathy)
Hearing assessment (PTA) and slit-lamp examination can clinch Alport syndrome without biopsy

Why TBMD and Alport Overlap — and How to Tell Them Apart

This is a frequent source of confusion. The reason they overlap is genetic: TBMD is caused by heterozygous COL4A3 or COL4A4 mutations — i.e. carriers of the autosomal recessive form of Alport syndrome carry one defective allele, which is enough to thin the GBM and cause haematuria, but not enough to cause the full progressive disease ^[5].

Some patients with heterozygous COL4A3/A4 mutations develop thin BM disease instead of Alport syndrome (reason unknown) ^[2]
In young children, early Alport syndrome can show GBM thinning only (before the basket-weave develops) — indistinguishable from TBMD on a single biopsy
Serial follow-up is key: TBMD stays stable; Alport progresses (proteinuria increases, GFR declines, hearing worsens)

Common Exam Mistake

Do NOT diagnose "thin basement membrane disease" from a single paediatric renal biopsy showing thin GBM — this may be early Alport syndrome. Always correlate with family history, PTA, genetic testing, and longitudinal follow-up.

When a patient has both nephropathy and sensorineural hearing loss, the differential narrows significantly:

Condition	Renal Feature	Hearing Feature	Key Differentiator
Alport syndrome	Progressive GN → ESRD	Bilateral high-frequency SNHL	Basket-weave GBM on EM; COL4A mutation; anterior lenticonus
Branchio-oto-renal (BOR) syndrome	Structural renal anomalies (renal agenesis, dysplasia, duplex collecting systems)	Mixed or SNHL + branchial cleft anomalies + preauricular pits/tags	EYA1 gene mutation; structural malformations rather than GN
CHARGE syndrome	Variable renal anomalies	SNHL (cochlear malformation)	Coloboma, heart defects, choanal atresia, genital/ear anomalies; CHD7 mutation
Distal RTA (Type 1) with SNHL	Nephrocalcinosis, metabolic acidosis, hypokalemia	SNHL	ATP6V1B1 or ATP6V0A4 mutation (encodes H+-ATPase in kidney AND cochlea); acidosis + stones, not haematuria-predominant ^[7]
Mitochondrial diseases (e.g., MELAS, MIDD)	FSGS, tubulopathy	SNHL (often maternal inheritance)	Maternal inheritance; lactic acidosis; diabetes mellitus; myopathy
Fabry disease	Proteinuria → CKD; podocyte inclusion bodies (zebra bodies on EM)	SNHL (variable)	X-linked; angiokeratomas, acroparaesthesias, cornea verticillata; α-galactosidase A deficiency
Bartter syndrome (neonatal)	Salt-wasting, hypokalaemic metabolic alkalosis, nephrocalcinosis	SNHL (Bartter type IV — BSND mutation)	Polyhydramnios, prematurity; alkalosis not acidosis; no haematuria ^[8]

The key differentiator for Alport is the combination of glomerular haematuria (not structural anomalies or tubulopathy) + progressive CKD + high-frequency SNHL + ocular abnormalities (especially anterior lenticonus).

Alport syndrome is one cause of CKD presenting in adolescence/young adulthood. When evaluating a young patient with unexplained CKD:

Causes of CKD (from CKD lecture) ^[6]:

Diabetes → 51% of CKD cases in HK ^[6]
Hypertension / vascular ^[6]
Chronic glomerulonephritis e.g. IgA GN ^[6]
Chronic pyelonephritis ^[6]
Polycystic kidney disease ^[6]
Drug-induced, TIN, TCM ^[6]
Myeloma (CRAB), monoclonal gammopathy ^[6]
Vasculitis, SLE, other autoimmune diseases ^[6]
Obstruction, kidney stones ^[6]
Alport's or other hereditary or rare diseases ^[6]
Obesity ^[6]

In a young patient specifically, the likely causes shift:

IgA nephropathy (most common primary GN worldwide)
Lupus nephritis (especially young females in Asia)
Alport syndrome (if FHx of renal failure + deafness)
FSGS (primary or secondary — including HIV-associated in endemic areas)
Reflux nephropathy
ADPKD (if family history + bilateral large cystic kidneys on imaging)

Since renal biopsy is sometimes performed before the clinical picture is clear, it helps to know what other conditions may be confused with Alport on biopsy:

Histological Finding	Alport Syndrome	Potential Mimics
Thin GBM (early)	Early Alport (especially in children)	TBMD (most common mimic); early diabetic nephropathy (uniform thickening later, not thinning)
Basket-weave GBM splitting (EM)	Classic Alport	Almost pathognomonic — no common mimic
Negative IF	Alport (non-immune)	TBMD (also negative); Minimal change disease (but no GBM changes); Pauci-immune crescentic GN (but crescents present)
FSGS pattern on LM (late)	Secondary FSGS from progressive Alport	Primary FSGS; HIV-associated FSGS; reflux nephropathy; obesity-related FSGS
Foam cells (interstitial)	Characteristic but not pathognomonic	Nephrotic syndrome of any cause (lipid-laden macrophages from heavy proteinuria)

This is a unique differential relevant to Alport patients who have received a renal transplant ^[5]:

May develop de novo anti-GBM disease (3%) after transplantation ^[5]
Mechanism: the donor kidney expresses normal α3-α4-α5 collagen IV — which the Alport patient's immune system has never been exposed to → the recipient may form anti-α5 (or anti-α3) antibodies that attack the graft GBM → crescentic GN ^[5]
This must be differentiated from transplant rejection (cellular or antibody-mediated) and recurrent disease (not applicable in Alport since the original disease is genetic, not immune)

Diagnostic Clue	Points Toward	Points Away From
FHx renal failure + deafness in males	Alport syndrome	TBMD, IgA nephropathy
Synpharyngitic haematuria (concurrent URTI)	IgA nephropathy	Alport (haematuria is persistent, not timed to URTI onset)
Anterior lenticonus	Alport (pathognomonic)	Everything else
Benign course, no proteinuria, no CKD	TBMD	Alport
Elevated serum IgA	IgA nephropathy	Alport, TBMD
Low C3	Lupus nephritis, MPGN, PSGN	Alport (complement is normal)
Structural renal anomalies	BOR syndrome, CHARGE	Alport (kidneys are structurally normal)
Metabolic acidosis + nephrocalcinosis + SNHL	Distal RTA with deafness	Alport
Angiokeratomas + acroparaesthesias	Fabry disease	Alport
Father-to-son transmission	AR or AD Alport (or non-Alport)	X-linked Alport ^[1]

High Yield Summary

Differential Diagnosis of Alport Syndrome — Exam Essentials:

Three classic causes of isolated glomerular haematuria: IgA nephropathy, Alport syndrome, TBMD — distinguish by FHx pattern, gross haematuria frequency, hearing/eye involvement, and EM findings.
TBMD vs early Alport: genetically related (heterozygous COL4A3/A4 carriers can present as either); differentiated by longitudinal course, genetic testing, and EM evolution.
Renal + deafness syndromes: BOR, CHARGE, distal RTA with SNHL, Fabry, mitochondrial diseases, Bartter type IV — each has distinct non-renal features that separate them from Alport.
Post-transplant: de novo anti-GBM disease in ~3% of Alport recipients (immune system attacks novel α3-α4-α5 collagen in graft).
Anterior lenticonus is pathognomonic — no other common condition in the DDx causes it.
Normal complement levels in Alport — if C3 is low, think lupus nephritis, MPGN, or PSGN instead.
History + urinalysis of family members ^[1] is the first-line distinguishing approach.

Active Recall - Differential Diagnosis of Alport Syndrome

References

Diagnostic Criteria, Diagnostic Algorithm & Investigations for Alport Syndrome

Unlike diseases such as SLE (which has formal ACR/EULAR classification criteria) or AKI (which has KDIGO staging), Alport syndrome is diagnosed through a combination of clinical features, family history, histopathology, and genetic testing. There is no universally accepted single-score diagnostic criterion. Instead, the diagnosis is established when a patient meets a sufficient constellation of findings. The 2013 Alport Syndrome Classification Working Group (later refined) proposed a practical framework that integrates clinical, pathological, and genetic data ^[2]^[4]^[9].

Think of it as a convergence of evidence approach — the more lines of evidence you have, the more certain the diagnosis.

Diagnostic Criteria Framework

The most widely used approach (adapted from the Alport Syndrome Classification Working Group / KDIGO guidelines) recognizes the diagnosis when at least one of the following is met:

Molecular genetic testing for COL4A3-5 mutations is now considered the first-line definitive diagnostic test ^[4]^[9].

Identification of a pathogenic or likely pathogenic variant in COL4A3, COL4A4, or COL4A5 confirms the diagnosis
With modern next-generation sequencing (NGS) panels, detection rate is > 90% in clinically suspected cases
Genetic testing also determines the inheritance pattern (X-linked vs AR vs AD) and can predict severity (truncating vs missense mutations)

A renal biopsy demonstrating:

Basket-weave appearance on EM (alternating thinning and thickening with splitting of lamina densa) ^[2]
AND/OR absent α3, α4, α5 collagen IV chain staining on immunofluorescence using chain-specific antibodies ^[2]
In the appropriate clinical context (haematuria ± proteinuria ± SNHL ± FHx)

The Flinter criteria require at least 3 of the following 4 features in a family:

#	Criterion	Rationale
1	Positive family history of macro/microscopic haematuria ± CKD progressing to ESRD	Establishes hereditary nature
2	Electron microscopy showing GBM splitting/lamellation (basket-weave) on renal biopsy	Characteristic histological finding
3	Progressive high-frequency sensorineural hearing loss (bilateral)	Cochlear basement membrane involvement
4	Characteristic ocular signs: anterior lenticonus, perimacular retinal flecks, or posterior polymorphous corneal dystrophy	Ocular basement membrane involvement

If only 2 criteria are met → "probable Alport syndrome" — genetic testing is essential
If the individual is a sporadic case (no FHx) → must rely on biopsy + genetics

Current Best Practice — Genetic-First Approach

In 2025 clinical practice, genetic testing has largely superseded renal biopsy as the primary diagnostic modality for suspected Alport syndrome, especially in children. Biopsy is reserved for cases where: (1) genetics are inconclusive, (2) there is significant proteinuria requiring histological characterisation, or (3) there is diagnostic uncertainty about other glomerulopathies.

The following algorithm integrates the clinical approach taught in HKUMed nephrology lectures ^[1]^[4]^[9]^[10]:

Investigation Modalities: Detailed Interpretation

Test	Expected Finding in Alport	Interpretation / Why
Urine dipstick	Blood positive (1+ to 3+), protein variable (trace to 2+)	Detects haemoglobin/myoglobin — must confirm with microscopy ^[9]^[10]
Urine microscopy	Dysmorphic RBCs, RBC casts	Dysmorphic RBCs = squeezed through damaged GBM (membrane distortion). RBC casts = RBCs trapped in Tamm-Horsfall protein in tubules, conforming to tubular shape. Diagnostic of glomerular origin ^[9]^[10]
Urine protein quantification	< 1–2 g/day initially ^[2]; may increase with disease progression	24-hour urine protein is the gold standard but cumbersome; urine protein-to-creatinine ratio (uPCR) or urine albumin-to-creatinine ratio (UACR) on spot morning sample is used clinically ^[10]
Urine culture, cytology, AFB	Should be negative	Exclusion of non-glomerular haematuria ^[4]: UTI, urinary tract TB, urothelial malignancy

Lecture Point — Urine Protein Quantification

Gold standard is 24-hour urine protein quantification → but very cumbersome. Urine protein-to-creatinine ratio (uPCR) measured on first morning void is the practical alternative. In QMH, uPCR is used instead of UACR ^[10]. UACR is preferred for diabetic nephropathy screening specifically.

All Hb-positive dipstick should be accompanied by urine microscopy to differentiate haematuria vs pigmenturia ^[3]

Test	Expected Finding	Interpretation
RFT (Na, K, Cl, urea, creatinine, eGFR)	Normal early; progressive rise in creatinine and fall in eGFR with age	Documents degree of renal impairment. When creatinine rises, GFR has already been reduced by at least 50% ^[11]
CBC	Usually normal early; normocytic normochromic anaemia develops with CKD	Anaemia of CKD (↓ erythropoietin from damaged kidneys). Not a primary feature of Alport itself
Serum albumin	Normal unless significant proteinuria develops	Low albumin → nephrotic range proteinuria (uncommon in Alport)
Serum complement (C3/C4)	Normal	Critical exclusionary test: ↓C3/C4 → lupus nephritis, MPGN, PSGN, cryoglobulinaemia. Normal C3/C4 generally indicates non-immune-complex-mediated GN ^[4]^[12]
ANA, anti-dsDNA	Negative	Excludes lupus nephritis ^[4]^[12]
ANCA	Negative	Excludes ANCA-associated vasculitis ^[4]^[12]
Anti-GBM antibodies	Negative	Excludes Goodpasture disease. Important: these antibodies target the α3 chain of collagen IV — the same chain that is absent in Alport patients (so Alport patients cannot form anti-GBM antibodies against their own GBM, but can after transplant) ^[4]^[12]
ASLO titre	Negative / not elevated	Excludes post-streptococcal GN ^[4]^[12]
HBV/HCV serology	Negative (unless concurrent infection)	Excludes viral-associated MPGN ^[4]^[12]
Serum IgA	Normal	Elevated in ~50% of IgA nephropathy — but not specific

Key Exam Point: Serology in Alport

Alport syndrome is NOT an immune-mediated disease. All autoimmune serologies (ANA, ANCA, anti-GBM, complement) should be normal. Serological testing is performed to exclude other glomerulonephritides that can mimic Alport's haematuria/proteinuria pattern. If serologies are positive, reconsider the diagnosis.

Hearing deficit common → pure-tone audiometry (PTA) ^[1]

Finding	Interpretation
Bilateral high-frequency sensorineural hearing loss (2000–8000 Hz initially)	Due to ↓ adhesion of Organ of Corti to basilar membrane via defective α-3-4-5 type IV collagen → high-tone deafness ^[1]^[2]
Normal PTA in young children	Does not exclude Alport — SNHL develops progressively (typically late childhood/adolescence). Repeat annually
Weber lateralises to better ear; Rinne positive bilaterally	Confirms sensorineural (not conductive) loss

PTA should be performed on every patient with suspected Alport syndrome AND all first-degree family members during cascade screening
Pure tone audiometry is the definitive clinical test for the hearing component of Alport syndrome ^[4]

Finding	Significance
Anterior lenticonus — "oil droplet" reflex on slit-lamp retroillumination	Virtually pathognomonic for Alport syndrome ^[2]^[4]. Forward bulging of lens due to weak capsule (defective collagen IV). No other common condition causes this.
Perimacular retinal flecks (dot-and-fleck retinopathy) — on fundoscopy	Common in Alport (~60–70% of X-linked males); due to abnormal Bruch's membrane ^[2]
Posterior polymorphous corneal dystrophy — on slit-lamp	Descemet's membrane involvement ^[2]
Recurrent corneal erosion	Defective corneal epithelial basement membrane adhesion ^[4]

Eye findings are not always present at initial presentation (especially in children) but develop with time
Annual ophthalmological review is recommended

Molecular genetic testing for COL4A3-5 mutations ^[4]:

Aspect	Detail
Genes tested	COL4A3 (chr 2), COL4A4 (chr 2), COL4A5 (chr X)
Method	Next-generation sequencing (NGS) panel covering all exons + intron-exon boundaries; ± MLPA (multiplex ligation-dependent probe amplification) for large deletions/duplications
Detection rate	> 90% in clinically suspected cases
Result categories	Pathogenic / Likely pathogenic / Variant of uncertain significance (VUS) / Likely benign / Benign
If pathogenic variant found	Diagnosis confirmed; determines inheritance pattern; informs prognosis (truncating = severe; missense = milder)
If VUS	Cannot confirm or exclude diagnosis — correlate with clinical/histological data; consider functional studies or re-classification over time
If negative	Consider deep intronic variants, mosaicism, or alternative diagnosis; renal biopsy may be needed

Why genetic testing first?

Non-invasive (blood draw)
Avoids renal biopsy in children (biopsy carries risk of bleeding, infection, and requires sedation/anaesthesia in young children)
Provides definitive inheritance pattern for genetic counselling of the family
Enables cascade screening of family members

Lecture Point — Genetic Testing vs Biopsy

Definitive tests: pure tone audiometry for Alport syndrome; molecular genetic testing for COL4A3-5 mutations in Alport syndrome or TBMD; kidney biopsy: usually reserved for those with significant proteinuria (> 1g/d) or other features of progressive renal diseases ^[4]

Kidney biopsy is usually reserved for those with significant proteinuria (> 1g/d) or other features ^[4] of progressive disease, or when genetic testing is inconclusive.

Contraindications to renal biopsy (relevant general principle) ^[10]:

Contracted/small kidneys (hard to find; may only yield fibrous tissue)
Large cysts (cannot stop the bleeding)
Solitary kidney (no backup if complication occurs)
Uncontrolled bleeding diathesis, severe uncontrolled hypertension

Biopsy Processing — Three Modalities:

Modality	Finding in Alport	Interpretation
Light Microscopy (LM)	Non-specific early; later focal ↑ cellularity, glomerulosclerosis (GS), tubulointerstitial fibrosis (TIF) ^[2]. May see foam cells (lipid-laden interstitial macrophages)	LM alone cannot diagnose Alport. Foam cells are suggestive but not pathognomonic
Electron Microscopy (EM)	Thinning (earliest), splitting of lamina densa (laminated), alternate thinning/thickening = basket-weave appearance ^[2]	Hallmark finding. In children may show only thinning (mimics TBMD) — severity increases with age. Normal GBM thickness is 300–400 nm; Alport shows irregular areas from < 150 nm to > 500 nm
Immunofluorescence (IF)	Should be negative on standard IF; negative for α3, α4, α5 chain immunostains if chain-specific antibodies are used ^[2]	Standard IF excludes immune-complex GN (IgA, lupus). Chain-specific staining distinguishes Alport from TBMD (TBMD retains normal α3-α4-α5 staining)

Collagen IV Chain Immunostaining — Pattern Interpretation:

Genotype	GBM staining	Bowman's capsule / EBM	Skin biopsy (epidermal BM)
XL male (COL4A5 mutation)	Absent α3, α4, α5	Absent α5	Absent α5
XL female carrier	Mosaic pattern (some segments +, some –) for α3, α4, α5	Mosaic α5	Mosaic α5
AR Alport (COL4A3 or A4 mutation)	Absent α3, α4; α5 may be present in Bowman's capsule	Variable	α5 present (since COL4A5 is normal)
TBMD (heterozygous COL4A3/A4)	Normal α3, α4, α5 staining	Normal	Normal

Why does absence of ONE chain cause absence of ALL three? The α3-α4-α5 network requires all three chains to form the triple helix. If α5 is absent (X-linked), α3 and α4 cannot be incorporated into the GBM and are degraded intracellularly → all three are absent on staining.

Skin Biopsy as a Surrogate

Skin biopsy of the epidermal basement membrane can be used as a less invasive alternative to renal biopsy for collagen IV chain immunostaining, particularly in X-linked Alport. The epidermal BM normally expresses α5 chain — absence on skin biopsy suggests COL4A5 mutation. However, skin biopsy has limitations in AR Alport (where α5 is normal in skin) and cannot provide EM or LM information about the kidneys.

Modality	Finding	Role
USG kidneys	Normal size early (10–12 cm); normal parenchymal echogenicity initially. Small kidneys with increased echogenicity + loss of corticomedullary differentiation in advanced CKD ^[10]^[6]	Best non-invasive way to assess and visualize kidneys ^[6]. Excludes obstruction, cysts (ADPKD), structural anomalies. Must confirm kidneys are not shrunken before biopsy
Doppler USG	Normal renal vasculature	Excludes renal artery stenosis as cause of hypertension

USG is performed before renal biopsy to ensure adequate kidney size and exclude contraindications ^[10]
Differential diagnosis of a small kidney on imaging: chronic kidney disease (dysplastic kidney, scarred/shrunken kidney) ^[6]
Normal-sized kidneys with high creatinine → worry about acute process (AKI, GN) → may need biopsy ^[6]

Test	Purpose
Calcium, phosphate, PTH, vitamin D	CKD-mineral bone disease (CKD-MBD) monitoring
Fasting glucose, HbA1c, lipid profile	Cardiovascular risk assessment (CKD patients have accelerated atherosclerosis)
Iron studies (ferritin, TSAT)	Anaemia of CKD workup
Serum/urine protein electrophoresis	Excludes myeloma kidney (relevant in older patients with CKD of unclear aetiology)

Once a proband is diagnosed, all first-degree relatives should be screened:

Test	Who	Why
Urinalysis (dipstick + microscopy)	All first-degree relatives	History + urinalysis of family members ^[1] — detect haematuria in carriers/affected individuals
RFT + BP	All first-degree relatives	Detect early CKD or hypertension
PTA	All first-degree relatives	Detect subclinical SNHL
Slit-lamp examination	All first-degree relatives	Detect ocular features
Genetic testing for the known familial mutation	At-risk relatives (especially in X-linked: all daughters of affected males; all sons/daughters of carrier females)	Definitive carrier identification; guides reproductive counselling

Important Counselling Point

Should evaluate carefully for any co-existent Alport syndrome before living-related donor transplantation ^[5]. A family member being considered as a living kidney donor must be genetically tested to confirm they are NOT a carrier — even if they have normal urinalysis. Carrier females (X-linked) often have haematuria but may still have near-normal renal function; however, donating a kidney may accelerate their progression to CKD.

Stage	Action	Key Test
1. Confirm glomerular haematuria	Urine dipstick + microscopy	Dysmorphic RBCs, RBC casts
2. Exclude non-glomerular causes	Urine culture, cytology, AFB; USG kidneys; ± cystoscopy	Negative for UTI, TB, stones, malignancy
3. Exclude other GN	Serology panel (C3/C4, ANA, ANCA, anti-GBM, ASLO, HBV/HCV)	All should be normal in Alport
4. Assess for extrarenal features	PTA + slit-lamp examination	High-frequency SNHL; anterior lenticonus
5. Definitive diagnosis	Genetic testing (COL4A3/A4/A5) ± renal biopsy with EM + chain-specific IF	Pathogenic mutation OR basket-weave GBM + absent α-chain staining
6. Cascade screening	Urinalysis, PTA, genetics for all first-degree relatives	Identify carriers and affected individuals

High Yield Summary

Diagnosis of Alport Syndrome — Exam Essentials:

No single diagnostic criterion — diagnosis by convergence of clinical, genetic, and histological evidence
Flinter criteria (clinical): ≥ 3 of 4: (i) FHx haematuria/ESRD, (ii) basket-weave GBM on EM, (iii) bilateral SNHL, (iv) ocular signs
Genetic testing = modern gold standard: COL4A3/A4/A5 sequencing; detection rate > 90%; determines inheritance and prognosis
Renal biopsy reserved for: proteinuria > 1g/day, inconclusive genetics, or diagnostic uncertainty. Must confirm normal kidney size on USG first
EM hallmark: basket-weave GBM (alternating thinning/thickening, lamina densa splitting)
IF: negative standard IF; absent α3-α4-α5 on chain-specific staining (XL males); mosaic in carrier females
PTA: essential — bilateral high-frequency SNHL; arrange for patient AND all family members
Anterior lenticonus on slit-lamp = virtually pathognomonic
All autoimmune serologies should be NORMAL — Alport is NOT immune-mediated; serologies are exclusionary
Cascade screening: urinalysis + PTA + genetics for all first-degree relatives; mandatory before considering living-related kidney donation

Active Recall - Diagnosis of Alport Syndrome

References

^[1] Senior notes: Block A - Glomerular and Tubulo-interstitial Diseases and Acute Kidney Injury.pdf (p10, Alport syndrome section) ^[2] Senior notes: Ryan Ho Urogenital.pdf (p60–61, Section 3.2.3 Alport Syndrome) ^[3] Senior notes: Maksim Medicine Notes.pdf (p230, Nephrology — haematuria section) ^[4] Senior notes: Ryan Ho Fundamentals.pdf (p358, Section 3.5.4 Isolated Glomerular Haematuria) ^[5] Senior notes: Ryan Ho Urogenital.pdf (p61, Management — transplant section) ^[6] Senior notes: Block A - Chronic Kidney Disease and its Complications.pdf (p8–13, Causes of CKD and kidney sizes) ^[9] Senior notes: Adrian Lui Pediatrics Notes.pdf (p323, Section 9.2.2 Approach to Isolated Hematuria) ^[10] Senior notes: Block A - Introduction to Renal Investigations (RFT, urine tests and US kidneys).pdf (p1–5) ^[11] Senior notes: Block A - Nephrology Interactive Tutorial.pdf (p3, creatinine interpretation) ^[12] Senior notes: Ryan Ho Urogenital.pdf (p63, Evaluation of nephritic syndrome — serology panel)

Management Algorithm & Treatment Modalities for Alport Syndrome

Before diving into specifics, understand the management philosophy for Alport syndrome:

There is no cure — Alport syndrome is a genetic structural defect in type IV collagen. You cannot fix the gene (yet).
No specific treatment exists ^[2] — management is about slowing progression and managing complications.
The disease trajectory is predictable: haematuria → proteinuria → hypertension → progressive CKD → ESRD → renal replacement therapy. Our job is to delay each transition for as long as possible.
The two pillars of management are: (a) RAAS inhibition to reduce proteinuria and slow CKD progression, and (b) renal transplantation when ESRD is reached.

Think of it like a bridge with structural cracks — you can't replace the steel, but you can reduce the traffic load (proteinuria/haemodynamic stress) to slow the collapse.

Treatment Modalities — Detailed Discussion

ACEI/ARB if overt proteinuria (UPCR > 2 mg/mg or proteinuria > 4 mg/m²/h) or male with high-risk mutations or microalbuminuria ^[2]

Why RAAS inhibition works in Alport syndrome:

The GBM in Alport is structurally defective and under constant haemodynamic stress from glomerular filtration pressure. The renin-angiotensin-aldosterone system (RAAS) contributes to:

Efferent arteriolar vasoconstriction → increased intraglomerular pressure → accelerated GBM damage
Podocyte injury via angiotensin II–mediated oxidative stress and TGF-β signalling → fibrosis
Proteinuria via increased filtration pressure across the damaged GBM

By blocking RAAS:

ACEI (e.g., ramipril, enalapril): inhibit angiotensin-converting enzyme → less angiotensin II → efferent arteriolar vasodilation → reduced intraglomerular pressure → less proteinuria → slower progression
ARB (e.g., losartan, valsartan): block angiotensin II type 1 receptors → same downstream effect

Aspect	Detail
Drug class	ACE inhibitor (first-line) or ARB (if ACEI-intolerant, e.g., persistent dry cough)
Examples	Ramipril 2.5–10 mg/day; enalapril 5–20 mg/day; losartan 25–100 mg/day
Indication	Overt proteinuria (UPCR > 2 mg/mg); or male with high-risk mutation; or microalbuminuria ^[2]
Target	Reduce proteinuria by ≥ 50% or to < 0.5 g/day; BP < 130/80 (adults) or < 90th percentile (children)
When to start	Current evidence (EARLY-PRO-TECT trial, 2022) supports starting at the microalbuminuria stage or even pre-emptively in high-risk males (truncating COL4A5 mutations) before overt proteinuria develops
Monitoring	Check serum K⁺ and creatinine 1–2 weeks after initiation or any dose change. Acceptable rise in creatinine: up to 20–30% from baseline (reflects haemodynamic effect). If > 30%, suspect other causes (bilateral renal artery stenosis, dehydration)

Contraindications to ACEI/ARB:

Absolute	Relative
Bilateral renal artery stenosis	Pre-existing hyperkalaemia (K⁺ > 5.5)
Pregnancy / women of childbearing age without contraception (teratogenic — renal agenesis, oligohydramnios)	Severe CKD (eGFR < 15) — can still be used cautiously with close monitoring
History of angioedema with ACEI (for ACEI specifically; can try ARB cautiously)	Hypotension (SBP < 90)
Allergy to the specific drug

Exam Point: Why NOT combine ACEI + ARB?

Dual RAAS blockade (ACEI + ARB together) was historically tried to maximise proteinuria reduction. However, the ONTARGET and VA NEPHRON-D trials showed that combination therapy increases the risk of hyperkalaemia, AKI, and hypotension without clear benefit in slowing CKD progression. Do not combine ACEI + ARB — use one or the other.

Aspect	Detail
Drug class	Sodium-glucose cotransporter-2 inhibitors
Examples	Dapagliflozin 10 mg/day; empagliflozin 10 mg/day
Mechanism	Block glucose and sodium reabsorption in proximal tubule → (a) afferent arteriolar vasoconstriction via tubuloglomerular feedback → reduced intraglomerular pressure (complements ACEI/ARB's efferent effect); (b) natriuresis; (c) anti-inflammatory and anti-fibrotic effects
Evidence	DAPA-CKD trial (2020) included patients with proteinuric CKD (some with Alport); showed 39% RR reduction in composite kidney endpoint. 2025 KDIGO guidelines recommend SGLT2i for proteinuric CKD regardless of aetiology
Indication in Alport	Add-on to ACEI/ARB when proteinuria remains > 0.5 g/day despite maximised RAAS inhibition, AND eGFR ≥ 20 mL/min
Contraindications	eGFR < 20 (can continue if already started and eGFR drops below); Type 1 diabetes (risk of DKA); recurrent genital infections
Monitoring	eGFR may dip 10–20% on initiation (haemodynamic, similar to ACEI) — acceptable and expected; stabilises after 2–4 weeks

Control hypertension ^[6] is a key therapeutic objective in CKD.

Target: < 130/80 mmHg in adults with proteinuria; < 90th percentile in children
First-line: ACEI or ARB (as above — dual benefit of BP lowering + renoprotection)
Add-on if needed: calcium channel blockers (amlodipine), beta-blockers, diuretics (loop or thiazide depending on eGFR)
Avoid thiazides once eGFR < 30 (ineffective); use loop diuretics (furosemide) instead
Low-salt diet (< 5 g/day NaCl) potentiates the effect of RAAS inhibitors

Measure	Rationale
Low-salt diet (< 5 g/day NaCl)	Potentiates ACEI/ARB effect; reduces BP and proteinuria
Adequate hydration	Maintains renal perfusion; avoids dehydration-induced AKI on top of CKD
Avoid nephrotoxins	NSAIDs, aminoglycosides, iodinated contrast — all worsen CKD. Consider and reverse use of any nephrotoxic drugs ^[13]
Exercise	Regular moderate exercise improves cardiovascular fitness (major cause of death in CKD patients is CV disease)
Smoking cessation	Smoking accelerates CKD progression and worsens cardiovascular risk
Hearing aids	For SNHL — referral to ENT/audiologist when PTA shows functionally significant loss. Does not halt progression but greatly improves quality of life
Ophthalmological management	Anterior lenticonus → progressive myopia/astigmatism → may need lens replacement surgery (phacoemulsification + IOL) when visual impairment is significant

Avoid Nephrotoxins — Practical List

Drug/Agent	Why Harmful	Alternative
NSAIDs	Inhibit prostaglandin-mediated afferent arteriolar vasodilation → ↓ GFR → AKI; also can cause interstitial nephritis	Paracetamol for analgesia
Aminoglycosides (gentamicin)	Direct proximal tubular toxicity	Use alternative antibiotics; if aminoglycoside essential, monitor drug levels and adjust for eGFR
Iodinated contrast	Contrast-induced nephropathy via renal vasoconstriction + direct tubular toxicity	Pre-hydration with IV saline; minimise contrast volume; use low-osmolality contrast; consider MRI (no iodine)
TCM / herbal remedies	Unpredictable nephrotoxicity (aristolochic acid nephropathy well-documented in HK)	Avoid entirely

As Alport syndrome progresses to CKD stages 3–5, the same CKD complications arise as in any CKD of other aetiologies. The management principles are identical:

Therapeutic objectives for CKD: delay kidney failure, control hypertension, reduce albuminuria, treat anaemia and MBD disorder, treat acidosis and high K, control lipid and CV risk ^[6]

Complication	Pathophysiology	Management
Anaemia of CKD	↓ erythropoietin production by damaged kidneys; iron deficiency from reduced absorption and chronic inflammation	Iron supplementation (IV iron if on dialysis; oral if pre-dialysis); erythropoiesis-stimulating agents (ESA) — epoetin alfa, darbepoetin — target Hb 10–11.5 g/dL (do NOT over-correct → thrombosis risk)
CKD-MBD (mineral bone disease)	↓ phosphate excretion → hyperphosphataemia; ↓ 1,25-dihydroxyvitamin D production → hypocalcaemia; → secondary hyperparathyroidism	Phosphate binders (calcium carbonate with meals, sevelamer, lanthanum); active vitamin D (calcitriol or alfacalcidol); calcimimetics (cinacalcet) for refractory secondary hyperPTH
Metabolic acidosis	↓ ammoniagenesis and ↓ bicarbonate regeneration by damaged tubules	Oral sodium bicarbonate (target serum HCO₃⁻ ≥ 22 mmol/L). Correcting acidosis slows CKD progression, improves muscle wasting, and reduces bone buffering
Hyperkalaemia	↓ K⁺ excretion by damaged distal nephrons; exacerbated by ACEI/ARB	Low-potassium diet; loop diuretics; potassium binders (sodium polystyrene sulphonate / patiromer / sodium zirconium cyclosilicate)
Cardiovascular risk	CKD is an independent CV risk factor (accelerated atherosclerosis, vascular calcification)	Statins (atorvastatin); BP control; smoking cessation; glucose control if diabetic; antiplatelet therapy if indicated
Fluid overload	↓ sodium and water excretion	Salt restriction; loop diuretics (furosemide); fluid restriction if severe

6. Renal Replacement Therapy — When ESRD is Reached

Renal transplant: preferred option over dialysis ^[2]

Aspect	Detail
Timing	Pre-emptive transplantation (before dialysis is needed) is ideal; typically planned when eGFR < 15–20 mL/min
Why preferred over dialysis	Better long-term survival, better quality of life, freedom from dialysis schedule, better cardiovascular outcomes
Living vs deceased donor	Living donor transplant has superior graft survival. However, in Alport syndrome, living-related donors must be carefully evaluated (see below)
Special considerations	Should evaluate carefully for any co-existent Alport syndrome before living-related donor transplantation ^[2]

Why is living-related donor evaluation critical in Alport?

Because the family members of an Alport patient may themselves be:

Affected (especially in AR Alport — siblings may be homozygous)
Carriers (in X-linked — all daughters of affected males are carriers; in AR — parents are obligate carriers)
Carrier females (X-linked) may have haematuria and subclinical disease that would worsen after uninephrectomy

Mandatory workup before accepting a living-related donor:

Genetic testing for the known familial COL4A mutation
Urinalysis (haematuria screening)
PTA (hearing loss screening)
Full renal function assessment (eGFR, proteinuria quantification)
If carrier status confirmed → NOT suitable as donor (unless fully counselled about risks and consented in exceptional circumstances)

May develop de novo anti-GBM disease (3%) as some may express anti-α5 or anti-α3 Ab → attack graft kidney GBM → crescentic GN ^[2]

Aspect	Detail
Mechanism	Alport patient's immune system has never been exposed to normal α3-α4-α5 collagen IV. The transplanted kidney expresses these "new" antigens → recipient forms anti-GBM antibodies (typically anti-α5 or anti-α3) → linear IgG deposition on graft GBM → crescentic GN
Frequency	~3% of transplanted Alport patients ^[2]
Risk factors	Males with X-linked Alport + truncating COL4A5 mutations (complete absence of α5 chain → strongest neoantigen response)
Timing	Usually within the first year post-transplant
Presentation	Rapid decline in graft function; haematuria; proteinuria; → graft biopsy shows crescentic GN with linear IgG on IF
Treatment	Plasmapheresis and cyclophosphamide ^[2] — same as treatment for native anti-GBM disease
Prognosis	Poor — often leads to graft loss despite treatment. If graft is lost, re-transplantation carries high risk of recurrence

Modality	Considerations
Haemodialysis	Requires AV fistula (ideally created ≥ 6 months before anticipated need); 3 sessions/week. Many Alport patients are young and active — HD significantly impacts lifestyle
Peritoneal dialysis	Home-based; preserves residual renal function longer; may suit younger patients for initial RRT; requires intact peritoneal membrane

Indications for dialysis initiation (same as any CKD → ESRD) — remember the mnemonic AEIOU ^[13]:

Acidosis: refractory metabolic acidosis (pH < 7.1)
Electrolytes: refractory hyperkalaemia (K⁺ > 6.5)
Intoxication: drug overdose requiring removal (less relevant in Alport)
Overload: fluid overload refractory to diuretics
Uraemia: uraemic symptoms (pericarditis, neuropathy, encephalopathy)

Therapy	Mechanism	Status (2025)
Bardoxolone methyl	Nrf2 activator → anti-inflammatory, anti-fibrotic effects in the kidney	Phase 3 trials (CARDINAL) showed improvement in eGFR but concerns about heart failure events. Not yet standard of care
Gene therapy	Corrective gene replacement or editing (CRISPR-based) for COL4A5	Preclinical studies; not yet in human trials for Alport
Chaperone therapy	Small molecules that stabilise misfolded collagen IV chains (for missense mutations)	Very early experimental stage
Anti-miR-21 (lademirsen)	Targets microRNA-21 which promotes fibrosis → reduces tubulointerstitial fibrosis	Phase 2 trials in Alport syndrome showed slowed GFR decline; Phase 3 trials underway

Aspect	Detail
When	At diagnosis and before any reproductive decisions
Key messages	Inheritance pattern (X-linked, AR, AD); recurrence risk for offspring; option of prenatal diagnosis or preimplantation genetic testing (PGT-M)
X-linked: affected father	All daughters will be carriers; no sons will be affected (they receive Y)
X-linked: carrier mother	50% chance each son is affected; 50% chance each daughter is a carrier
AR: both parents carriers	25% chance affected; 50% carrier; 25% unaffected
Reproductive options	PGT-M with IVF; prenatal testing (amniocentesis/CVS); natural conception with postnatal testing

Stage	Key Features	Management Priority
Haematuria only	Microscopic haematuria, normal RFT, no proteinuria	Annual monitoring; consider pre-emptive ACEI in high-risk males; avoid nephrotoxins; cascade screening
Microalbuminuria / proteinuria	uPCR rising; eGFR still normal or mildly reduced	ACEI/ARB — titrate to max dose; add SGLT2i if proteinuria persists; low-salt diet; BP control
Established CKD	Declining eGFR; hypertension; proteinuria increasing	Continue ACEI/ARB + SGLT2i; manage CKD complications (anaemia, MBD, acidosis, hyperkalaemia, CV risk); transplant workup
ESRD	eGFR < 15; uraemic symptoms	Renal transplant (preferred) ^[2]; dialysis as bridge or alternative; monitor for de novo anti-GBM disease post-transplant
All stages	Extrarenal features	Hearing aids for SNHL; ophthalmological management; genetic counselling

High Yield Summary

Management of Alport Syndrome — Exam Essentials:

No specific treatment exists ^[2] — management is supportive + renoprotective
ACEI/ARB is the cornerstone: start at microalbuminuria (or pre-emptively in high-risk males); titrate to max tolerated dose; target proteinuria reduction ≥ 50%
SGLT2 inhibitors are emerging add-on therapy (DAPA-CKD evidence) — add when proteinuria persists despite maximal ACEI/ARB
Avoid nephrotoxins: NSAIDs, aminoglycosides, iodinated contrast, TCM
CKD complications: treat anaemia (iron + ESA), CKD-MBD (phosphate binders + vitamin D), acidosis (bicarbonate), hyperkalaemia, CV risk (statins)
Renal transplant is the preferred RRT over dialysis ^[2]
Evaluate family members carefully before living-related donation — genetic testing mandatory to exclude carrier status ^[2]
De novo anti-GBM disease occurs in ~3% post-transplant — treat with plasmapheresis and cyclophosphamide ^[2]
Hearing aids for SNHL; lens surgery for anterior lenticonus if visually significant
Genetic counselling is essential — discuss inheritance, recurrence risk, PGT-M options

Active Recall - Management of Alport Syndrome

References

^[2] Senior notes: Ryan Ho Urogenital.pdf (p60–61, Section 3.2.3 Alport Syndrome — diagnosis and management) ^[6] Senior notes: Block A - Chronic Kidney Disease and its Complications.pdf (p8–17, CKD therapy aims) ^[10] Senior notes: Block A - Introduction to Renal Investigations (RFT, urine tests and US kidneys).pdf (p4–5, urine protein quantification and imaging) ^[13] Senior notes: Ryan Ho Critical Care.pdf (p26, Immediate approach to AKI and dialysis indications)

Complications of Alport Syndrome

Complications of Alport syndrome can be understood as falling into two broad categories: (1) complications arising directly from the underlying collagen IV defect itself (extrarenal manifestations), and (2) complications arising as consequences of progressive CKD and eventually ESRD — which are the same complications seen in CKD of any aetiology. There is also a unique third category: (3) post-transplant complications specific to Alport syndrome.

Think of it this way: the collagen defect is the "first hit" that damages the GBM, cochlea, and eye directly. Then progressive renal damage from the defective GBM leads to a cascade of CKD complications (the "second hit"). Finally, when the patient reaches ESRD and receives a transplant, the immune system encounters collagen IV for the "first time," generating a unique "third hit."

1. Renal Complications (Direct Disease Progression)

This is the most significant complication and the main cause of morbidity.

Feature	Detail	Pathophysiological Basis
Progressive CKD: GBM damage → secondary glomerulosclerosis (GS) + tubulointerstitial fibrosis (TIF) → proteinuria and progressive CKD ^[2]	ESRD usually occurs at 16–35 years old (for X-linked and AR cases); AD cases typically > 45 years ^[2]	The defective α1-α1-α2 embryonic GBM is susceptible to endoproteolysis → cycles of damage and attempted repair → glomerulosclerosis. Damaged glomeruli release pro-fibrotic cytokines (TGF-β) → tubulointerstitial fibrosis → nephron loss → CKD → ESRD
Rate of progression depends on genotype	Truncating COL4A5 mutations: ESRD by ~20y. Missense mutations: ESRD by ~30y. AD heterozygous: ESRD > 45y	Complete absence of α5 chain (truncating) → no α3-4-5 network at all → faster GBM deterioration than missense mutations where a partially functional network exists
Proteinuria increases with age	Starts as microalbuminuria → overt proteinuria (< 1–2 g/day) → can occasionally reach nephrotic range	Progressive podocyte injury from ongoing GBM damage → widening of slit diaphragm gaps → increasing protein leak

Develops in adolescence or early adulthood as nephron loss progresses
Mechanism: progressive glomerulosclerosis → sodium retention + RAAS activation → volume expansion + vasoconstriction → hypertension
Hypertension itself accelerates CKD progression (vicious cycle): ↑BP → ↑intraglomerular pressure → more GBM damage → more nephron loss → more hypertension
High blood pressure is listed as a key systemic complication of CKD ^[6]

Alport patients with already-compromised renal reserve are highly vulnerable to AKI from:
- Nephrotoxic drugs (NSAIDs, aminoglycosides, iodinated contrast)
- Dehydration (intercurrent illness, vomiting, diarrhoea)
- Urinary tract infections
Even a "mild" insult that a normal kidney could handle may cause significant AKI in an Alport patient because the remaining nephrons are already maximally compensating

Once CKD develops (typically CKD stages 3–5), the same complications seen in any cause of CKD emerge. These are well-covered in the CKD lectures ^[6]:

Six systemic complications of chronic kidney disease: fluid retention, metabolic acidosis, high blood pressure, normochromic normocytic anaemia, secondary hyperparathyroidism, bone disease ^[6]

Mechanism	Clinical Features	Why It Matters in Alport
↓ Erythropoietin (EPO) production by damaged peritubular interstitial cells in the renal cortex → ↓ RBC production	Normochromic normocytic anaemia ^[6]: fatigue, pallor, exercise intolerance, dyspnoea on exertion	Alport patients are often young and active — anaemia significantly impairs quality of life. Also, anaemia worsens cardiac workload → contributes to LVH and heart failure over time

Additional contributing factors:

Iron deficiency (reduced absorption, chronic inflammation)
Uraemic toxins suppress erythropoiesis and shorten RBC lifespan
Chronic inflammation → hepcidin elevation → functional iron deficiency

Secondary hyperparathyroidism + bone disease ^[6]

Step	Mechanism
1	Damaged kidneys cannot excrete phosphate → hyperphosphataemia
2	Damaged kidneys cannot hydroxylate 25-OH vitamin D to active 1,25-(OH)₂ vitamin D (calcitriol) → ↓ calcitriol
3	↓ Calcitriol → ↓ intestinal calcium absorption → hypocalcaemia
4	Hypocalcaemia + hyperphosphataemia + ↓ calcitriol → all stimulate parathyroid gland → secondary hyperparathyroidism ^[6]
5	↑ PTH → increased bone resorption → renal osteodystrophy (osteitis fibrosa cystica, osteomalacia, adynamic bone disease, mixed)
6	Hyperphosphataemia + hypercalcaemia (from PTH-driven bone resorption) → vascular calcification → ↑ cardiovascular risk

In Alport patients, CKD-MBD is particularly concerning because they reach ESRD at a young age (16–35y) — meaning they accumulate decades of bone and vascular damage if not managed early
CKD resulting in poor activation of Vit D, so hypocalcemia and hyperphosphatemia → body releases more PTH, secondary hyperPTH ^[6]

Fluid retention ^[6]:

↓ sodium and water excretion → volume expansion → peripheral oedema, hypertension, pulmonary oedema (if severe)
Chronic volume overload + hypertension + anaemia → left ventricular hypertrophy (LVH) → eventual heart failure
CKD is an independent cardiovascular risk factor — patients with CKD have accelerated atherosclerosis
For young Alport patients reaching ESRD in their 20s–30s, cardiovascular disease becomes a leading cause of mortality if they survive to middle age

Metabolic acidosis ^[6]:

Damaged tubules lose ability to generate ammonia (ammoniagenesis) and regenerate bicarbonate
Results in non-anion gap metabolic acidosis initially (similar to type 4 RTA), progressing to high anion gap metabolic acidosis as GFR falls below ~15–20 mL/min (retention of sulphate, phosphate, and other unmeasured anions)
Consequences: muscle wasting (catabolism), bone buffering (worsens CKD-MBD), accelerated CKD progression

Electrolyte	Abnormality	Mechanism	Clinical Significance
Potassium	Hyperkalaemia	↓ distal tubular K⁺ excretion (especially with ACEI/ARB use)	Potentially life-threatening: cardiac arrhythmias (peaked T waves → widened QRS → VF/asystole). Particularly dangerous because Alport patients are on ACEI/ARB as cornerstone therapy
Sodium	Variable (often hyponatraemia in advanced CKD)	Dilutional (water retention exceeds sodium retention)	Oedema, confusion if severe
Calcium	Hypocalcaemia	↓ calcitriol production (see CKD-MBD above)	Tetany, perioral tingling, QT prolongation
Phosphate	Hyperphosphataemia	↓ renal phosphate excretion	Vascular calcification, pruritus, worsens hyperPTH

At very advanced CKD (eGFR < 10–15):

Accumulation of uraemic toxins (urea, creatinine, indoxyl sulphate, p-cresyl sulphate, etc.)
Uraemic syndrome: nausea, vomiting, anorexia, metallic taste, uraemic frost (urea crystals on skin), asterixis, pericarditis (uraemic pericarditis — friction rub), encephalopathy, peripheral neuropathy, platelet dysfunction (uraemic bleeding)
Uraemic pericarditis is an indication for urgent dialysis

CKD causes immune dysfunction (impaired neutrophil function, lymphocyte dysfunction, complement dysregulation)
Uraemia itself is immunosuppressive
Particularly relevant when patients are on immunosuppression post-transplant (see below)

3. Extrarenal Complications (Direct Collagen IV Defect)

These are not "complications" of CKD per se — they are primary manifestations of the collagen IV defect in non-renal tissues. However, they are clinically managed as complications that impact the patient's overall health:

Cochlea — ↓ adhesion of the Organ of Corti (the auditory sensory cells) to the basilar membrane via the defective alpha-3-4-5 type IV collagen ^[1]^[14]

Feature	Detail
Pattern	Bilateral high-frequency SNHL, progressing to involve lower frequencies ^[2]
Onset	Late childhood / adolescence (not present at birth)
Progression	Gradual and irreversible — eventually may become severe enough to impair daily communication
Impact	Social isolation, academic difficulties in children/adolescents, occupational impairment in adults
Management	Hearing aids (amplification devices); cochlear implants in severe cases. The hearing loss is structural (basement membrane defect), not amenable to medical treatment

Complication	Mechanism	Clinical Impact
Anterior lenticonus ^[2]	Weakness of anterior lens capsule (defective collagen IV) → forward lens bulging	Progressive myopia, irregular astigmatism; eventually may require phacoemulsification + IOL implantation
Perimacular retinal flecks ^[2]	Abnormal Bruch's membrane (collagen IV) → yellow-white deposits around macula	Usually does not significantly impair vision; important as a diagnostic sign
Posterior polymorphous corneal dystrophy ^[2]	Defective Descemet's membrane (collagen IV in corneal basement membrane) → vesicular endothelial lesions	Rarely vision-threatening; may cause mild corneal oedema in severe cases
Recurrent corneal erosion ^[4]	Defective adhesion of corneal epithelium to its basement membrane	Painful episodes of corneal epithelial sloughing; treated with lubricants, bandage contact lenses
Cataracts	May develop earlier than general population (lens capsule vulnerability)	Managed with standard cataract surgery when visually significant

Leiomyomatosis in 2–5% of Alport patients ^[2]
Occurs in a specific genetic subtype: contiguous gene deletion involving both COL4A5 and COL4A6 on Xq22
Benign smooth muscle tumours develop in:
- Oesophagus → dysphagia, retrosternal pain
- Tracheobronchial tree → cough, stridor (rare)
- Female genital tract (vulva, clitoris, uterus) → pelvic mass, menorrhagia
Management: surgical excision if symptomatic; surveillance imaging if asymptomatic

Thoracic/abdominal aortic aneurysms ^[2] — rare but recognised
Defective collagen IV in vascular basement membranes → structural weakness of the aortic wall → aneurysmal dilatation
Risk of rupture or dissection — though much rarer than in Marfan syndrome (which affects fibrillin-1 rather than collagen IV)

4. Post-Transplant Complications (Unique to Alport Syndrome)

May develop de novo anti-GBM disease (3%) as some may express anti-α5 or anti-α3 Ab → attack graft kidney GBM → crescentic GN → plasmapheresis and cyclophosphamide ^[2]

Feature	Detail
Mechanism	Alport patients have never been exposed to normal α3-α4-α5 collagen IV (their own kidneys never produced it). The transplanted kidney expresses these "neoantigens" → the recipient's immune system recognises them as foreign → forms anti-GBM antibodies (usually anti-α5 or anti-α3) → linear IgG deposition on graft GBM → crescentic GN
Frequency	~3% of transplanted Alport patients ^[2]
Risk factors	X-linked males with truncating COL4A5 mutations (complete absence of α5 = strongest neoantigen stimulus). AR patients with complete absence of α3 or α4 also at risk
Timing	Usually within 1st year post-transplant
Presentation	Rapid graft dysfunction, haematuria, proteinuria
Diagnosis	Graft biopsy: crescentic GN with linear IgG staining on IF + circulating anti-GBM antibodies
Treatment	Plasmapheresis (remove circulating anti-GBM antibodies) + cyclophosphamide (halt further antibody production) ^[2]^[15]
Prognosis	Often leads to graft loss despite treatment. Re-transplantation carries risk of recurrence

Key Concept: Why Anti-GBM Disease Cannot Occur in Native Alport Kidneys

Anti-GBM disease (Goodpasture disease) targets the NC1 domain of α3 collagen IV in the GBM. In Alport syndrome, the α3-α4-α5 network is absent from the patient's own GBM — the antigen simply does not exist. Therefore, anti-GBM disease cannot develop in native Alport kidneys. It can only occur post-transplant when the donor kidney introduces the "missing" collagen IV chains for the first time.

These are not specific to Alport but apply to all renal transplant recipients:

Long-term complications following kidney transplant ^[16]:

Infections — CMV, PJP, BK virus, MTB ^[16]: due to immunosuppression (tacrolimus, MMF, steroids)
Malignancy — PTLD (B-cell lymphoma, EBV-related) ^[16]: EBV-driven lymphoproliferation in immunosuppressed patients
Cardiovascular disease ^[16]: accelerated atherosclerosis from immunosuppressive drug effects (dyslipidaemia, diabetes), hypertension, and residual CKD-MBD
Drug-related side effects ^[16]: calcineurin inhibitor nephrotoxicity, steroid side effects (cushingoid features, osteoporosis, diabetes), mycophenolate (GI side effects, cytopenias)
Chronic allograft injury ^[16]: leading cause of late graft failure — progressive interstitial fibrosis and tubular atrophy from both immune (chronic rejection) and non-immune (calcineurin inhibitor toxicity, hypertension) factors
Recurrence of primary disease ^[16]: not applicable in the traditional sense for Alport (it's genetic, not immune), but de novo anti-GBM disease is the Alport-specific equivalent

Often overlooked but critically important in Alport syndrome because patients are young:

Complication	Context
Depression and anxiety	Chronic disease diagnosed in childhood; facing progressive kidney failure, hearing loss, and visual problems during formative years
Educational and occupational impact	SNHL impairs academic performance; recurrent medical appointments disrupt schooling; ESRD requiring dialysis limits employment
Reproductive concerns	Genetic disease → burden of reproductive decision-making; carrier females face uncertainty about their own disease progression (lyonization)
Body image and social isolation	Hearing aids, cushingoid appearance (if on steroids post-transplant), dialysis access (AV fistula), oedema
Financial burden	Lifelong medical care, dialysis costs, transplant medications

System	Complication	Mechanism
Renal	Progressive CKD → ESRD	GBM defect → glomerulosclerosis + TIF
Renal	Hypertension	Nephron loss → sodium retention + RAAS activation
Haematological	Normochromic normocytic anaemia	↓ EPO production by damaged kidneys
Bone/Mineral	Secondary hyperPTH, renal osteodystrophy	↓ calcitriol + hyperphosphataemia → hypocalcaemia
Cardiovascular	LVH, heart failure, accelerated atherosclerosis	Chronic volume overload + HTN + anaemia + dyslipidaemia
Metabolic	Acidosis, hyperkalaemia	↓ tubular H⁺ and K⁺ excretion
Auditory	Bilateral high-frequency SNHL	Defective cochlear basement membrane
Ocular	Anterior lenticonus, retinal flecks, corneal dystrophy	Defective collagen IV in lens capsule, Bruch's membrane, Descemet's membrane
Smooth muscle	Leiomyomatosis (oesophagus, tracheobronchial tree, genital tract)	Contiguous COL4A5 + COL4A6 deletion
Vascular	Thoracic/abdominal aortic aneurysms	Defective vascular basement membrane collagen IV
Post-transplant	De novo anti-GBM disease (~3%)	Neoantigen (normal α3-α4-α5 collagen) in graft → anti-GBM antibodies
Post-transplant	Infections, malignancy, drug toxicity, chronic allograft injury	Immunosuppression-related (general transplant complications)
Psychosocial	Depression, educational/occupational impairment, reproductive anxiety	Chronic disease in young patients

High Yield Summary

Complications of Alport Syndrome — Exam Essentials:

Progressive CKD → ESRD is the principal complication: GBM defect → glomerulosclerosis + TIF → ESRD by age 16–35 (XL males, AR) or > 45 (AD)
CKD complications are identical to CKD of any cause: anaemia (↓ EPO), CKD-MBD (secondary hyperPTH), fluid overload, metabolic acidosis, hyperkalaemia, CV disease
Extrarenal complications are DIRECT collagen IV defects — not secondary to CKD: SNHL (cochlear BM), anterior lenticonus (lens capsule), retinal flecks (Bruch's membrane), leiomyomatosis (COL4A5+A6 deletion), aortic aneurysms
De novo anti-GBM disease post-transplant (~3%): unique to Alport — recipient immune system attacks normal α3-α4-α5 collagen IV in graft → crescentic GN → treat with plasmapheresis + cyclophosphamide
Psychosocial burden is major — young patients facing lifelong progressive disease affecting kidneys, hearing, and vision
Hyperkalaemia risk is compounded by ACEI/ARB use (cornerstone treatment) in the setting of declining renal function — requires careful monitoring

Active Recall - Complications of Alport Syndrome

References

^[1] Lecture slides: GC 057. Glomerular and Tubulo-interstitial Diseases and Acute Kidney Injury.pdf (p18, Alport syndrome slide) ^[2] Senior notes: Ryan Ho Urogenital.pdf (p60–61, Section 3.2.3 Alport Syndrome) ^[4] Senior notes: Ryan Ho Fundamentals.pdf (p358, Section 3.5.4 Isolated Glomerular Haematuria) ^[6] Senior notes: Block A - Chronic Kidney Disease and its Complications.pdf (p23, systemic complications of CKD) ^[14] Senior notes: Block A - Glomerular and Tubulo-interstitial Diseases and Acute Kidney Injury.pdf (p10, Alport syndrome section) ^[15] Senior notes: Block A – Nephrology Data Interpretation.pdf (p15, Treatment of Goodpasture's syndrome) ^[16] Senior notes: Block A - Renal Replacement Therapies.pdf (p36–40, Long-term complications of renal transplant)

High Yield Summary

Alport Syndrome — Key Points for Exams:

Definition: Inherited type IV collagen disorder (COL4A3/A4/A5) → defective α3-α4-α5 collagen IV network in GBM, cochlea, eye
Inheritance: X-linked 80% (COL4A5), AR 15% (COL4A3/A4), AD < 5%
No father-to-son transmission in X-linked form
Female carriers (X-linked): almost all have haematuria, some develop renal failure (lyonization)
Pathogenesis: Absent α3-4-5 network → persistence of embryonic α1-1-2 network → susceptible to proteolysis → GBM splitting → basket-weave on EM → GS + TIF → CKD → ESRD
Clinical triad: Haematuria/CKD + SNHL (high-tone first) + ocular abnormalities (anterior lenticonus = pathognomonic)
EM: Basket-weave GBM (alternating thinning/thickening, lamina densa splitting)
IF: Negative (NOT immune-mediated)
PTA: Investigation of choice for hearing loss
Distinguished from TBMD: TBMD is AD, benign course, thin GBM, no hearing/eye involvement; Alport progresses to ESRD
ESRD age: 16–35y (XL males, AR); > 45y (AD)

High Yield Summary

Differential Diagnosis of Alport Syndrome — Exam Essentials:

Three classic causes of isolated glomerular haematuria: IgA nephropathy, Alport syndrome, TBMD — distinguish by FHx pattern, gross haematuria frequency, hearing/eye involvement, and EM findings.
TBMD vs early Alport: genetically related (heterozygous COL4A3/A4 carriers can present as either); differentiated by longitudinal course, genetic testing, and EM evolution.
Renal + deafness syndromes: BOR, CHARGE, distal RTA with SNHL, Fabry, mitochondrial diseases, Bartter type IV — each has distinct non-renal features that separate them from Alport.
Post-transplant: de novo anti-GBM disease in ~3% of Alport recipients (immune system attacks novel α3-α4-α5 collagen in graft).
Anterior lenticonus is pathognomonic — no other common condition in the DDx causes it.
Normal complement levels in Alport — if C3 is low, think lupus nephritis, MPGN, or PSGN instead.
History + urinalysis of family members ^[1] is the first-line distinguishing approach.

High Yield Summary

Diagnosis of Alport Syndrome — Exam Essentials:

No single diagnostic criterion — diagnosis by convergence of clinical, genetic, and histological evidence
Flinter criteria (clinical): ≥ 3 of 4: (i) FHx haematuria/ESRD, (ii) basket-weave GBM on EM, (iii) bilateral SNHL, (iv) ocular signs
Genetic testing = modern gold standard: COL4A3/A4/A5 sequencing; detection rate > 90%; determines inheritance and prognosis
Renal biopsy reserved for: proteinuria > 1g/day, inconclusive genetics, or diagnostic uncertainty. Must confirm normal kidney size on USG first
EM hallmark: basket-weave GBM (alternating thinning/thickening, lamina densa splitting)
IF: negative standard IF; absent α3-α4-α5 on chain-specific staining (XL males); mosaic in carrier females
PTA: essential — bilateral high-frequency SNHL; arrange for patient AND all family members
Anterior lenticonus on slit-lamp = virtually pathognomonic
All autoimmune serologies should be NORMAL — Alport is NOT immune-mediated; serologies are exclusionary
Cascade screening: urinalysis + PTA + genetics for all first-degree relatives; mandatory before considering living-related kidney donation

High Yield Summary

Management of Alport Syndrome — Exam Essentials:

No specific treatment exists ^[2] — management is supportive + renoprotective
ACEI/ARB is the cornerstone: start at microalbuminuria (or pre-emptively in high-risk males); titrate to max tolerated dose; target proteinuria reduction ≥ 50%
SGLT2 inhibitors are emerging add-on therapy (DAPA-CKD evidence) — add when proteinuria persists despite maximal ACEI/ARB
Avoid nephrotoxins: NSAIDs, aminoglycosides, iodinated contrast, TCM
CKD complications: treat anaemia (iron + ESA), CKD-MBD (phosphate binders + vitamin D), acidosis (bicarbonate), hyperkalaemia, CV risk (statins)
Renal transplant is the preferred RRT over dialysis ^[2]
Evaluate family members carefully before living-related donation — genetic testing mandatory to exclude carrier status ^[2]
De novo anti-GBM disease occurs in ~3% post-transplant — treat with plasmapheresis and cyclophosphamide ^[2]
Hearing aids for SNHL; lens surgery for anterior lenticonus if visually significant
Genetic counselling is essential — discuss inheritance, recurrence risk, PGT-M options

High Yield Summary

Complications of Alport Syndrome — Exam Essentials:

Progressive CKD → ESRD is the principal complication: GBM defect → glomerulosclerosis + TIF → ESRD by age 16–35 (XL males, AR) or > 45 (AD)
CKD complications are identical to CKD of any cause: anaemia (↓ EPO), CKD-MBD (secondary hyperPTH), fluid overload, metabolic acidosis, hyperkalaemia, CV disease
Extrarenal complications are DIRECT collagen IV defects — not secondary to CKD: SNHL (cochlear BM), anterior lenticonus (lens capsule), retinal flecks (Bruch's membrane), leiomyomatosis (COL4A5+A6 deletion), aortic aneurysms
De novo anti-GBM disease post-transplant (~3%): unique to Alport — recipient immune system attacks normal α3-α4-α5 collagen IV in graft → crescentic GN → treat with plasmapheresis + cyclophosphamide
Psychosocial burden is major — young patients facing lifelong progressive disease affecting kidneys, hearing, and vision
Hyperkalaemia risk is compounded by ACEI/ARB use (cornerstone treatment) in the setting of declining renal function — requires careful monitoring

Alport Syndrome

Definition

Epidemiology

Risk Factors

Anatomy & Function: Type IV Collagen and the GBM

The Glomerular Basement Membrane (GBM)

Type IV Collagen: The Six α-Chains

The Cochlea

The Eye

Aetiology & Genetics

Inheritance Patterns

Gene-Phenotype Correlation

Pathophysiology

Step-by-Step Pathogenesis [2]

In the Cochlea

In the Eye

Classification

By Inheritance Pattern (as above)

By Clinical Phenotype

Clinical Features

A. Symptoms (with pathophysiological basis)

Renal Symptoms

Hearing Symptoms

Ocular Symptoms

B. Signs (with pathophysiological basis)

Renal Signs

Audiological Signs

Ocular Signs

Other Signs

Histopathology

Light Microscopy (LM)

Electron Microscopy (EM) — The Definitive Histological Finding

Immunofluorescence (IF)

Distinguishing the Three Causes of Isolated Glomerular Haematuria

Summary of the Natural History

Active Recall - Alport Syndrome

References

1. Differential Diagnosis of Persistent Glomerular Haematuria

2. Differential Diagnosis of Renal Disease + Deafness (Renal-Auditory Syndromes)

3. Differential Diagnosis of CKD in a Young Person (Broader Framework)

4. Differential Diagnosis by Histological Pattern

5. Post-Transplant Differential: De Novo Anti-GBM Disease

Diagnostic Approach Algorithm

Summary Table: Key Differentiators

Active Recall - Differential Diagnosis of Alport Syndrome

Preamble: Why Alport Syndrome Has No Single "Diagnostic Criterion Set"

Diagnostic Criteria Framework

A. Genetic Diagnosis (Gold Standard — 2025 Approach)

B. Histological Diagnosis (If Genetic Testing Unavailable or Inconclusive)

C. Clinical Diagnosis (Historical Criteria — Modified Flinter Criteria, 1988)

Diagnostic Algorithm

Investigation Modalities: Detailed Interpretation

1. Urinalysis — The Starting Point

2. Blood Tests — Baseline and Exclusionary

3. Pure Tone Audiometry (PTA) — Essential for Alport

4. Ophthalmological Examination — Slit-Lamp + Fundoscopy

5. Genetic Testing — The Modern Gold Standard

6. Renal Biopsy — When Needed

7. Renal Imaging

8. Additional Tests for CKD Staging and Complications (When CKD Develops)

9. Cascade Family Screening

Summary: Staged Diagnostic Approach

Active Recall - Diagnosis of Alport Syndrome

Overarching Principles

Management Algorithm

Treatment Modalities — Detailed Discussion

1. RAAS Inhibition: ACE Inhibitors and ARBs — The Cornerstone

2. SGLT2 Inhibitors — Emerging Add-On Therapy

3. Blood Pressure Control — Beyond RAAS Inhibition

4. Supportive / Lifestyle Measures

5. Management of CKD Complications

6. Renal Replacement Therapy — When ESRD is Reached

6a. Renal Transplantation — First-Line RRT

6b. De Novo Anti-GBM Disease Post-Transplant

6c. Dialysis — As Bridge or Alternative

7. Emerging / Experimental Therapies

8. Genetic Counselling

Summary: Management by Disease Stage

Active Recall - Management of Alport Syndrome

1. Renal Complications (Direct Disease Progression)