Oculocutaneous Albinism

Oculocutaneous albinism (OCA) is a heterogeneous group of autosomal recessive disorders of melanin biosynthesis that affects the skin, hair and eyes. For NEET PG, the high-yield axes are the type-wise genetics (tyrosinase vs P-gene), the syndromic associations with bleeding and immunodeficiency, and the relentless lifelong risk of cutaneous malignancy.

Definition & basic biology

Albinism is a congenital, inherited reduction or complete absence of melanin pigment due to a defect in one of the enzymes or transport proteins of the melanin synthesis pathway. The melanocyte number is normal — the defect is purely in pigment production, not in the cell itself (this distinguishes albinism from vitiligo, where melanocytes are destroyed).

Melanin is synthesised inside melanosomes from the amino acid tyrosine:

Tyrosine → (tyrosinase) → DOPA → (tyrosinase) → dopaquinone → eumelanin (brown-black) / pheomelanin (red-yellow)

The rate-limiting and central enzyme is tyrosinase, encoded by the TYR gene. A defect anywhere along this chain — enzyme, transporter, or melanosome-biogenesis protein — produces an albinism phenotype.

High-yield: In albinism the number of melanocytes is normal; only melanin synthesis is defective. In vitiligo and piebaldism the melanocytes themselves are absent.

Classification of OCA

Classically OCA was split by the historical tyrosinase (hair-bulb) test into tyrosinase-negative and tyrosinase-positive types. Modern classification is gene-based (OCA1–OCA8). The four most tested are below.

Type	Gene / Protein	Tyrosinase activity	Phenotype	Key clue
OCA1	TYR (tyrosinase)	Absent (OCA1A) / reduced (OCA1B)	Most severe; white hair, milk-white skin, blue/grey iris, marked nystagmus	OCA1A = "true albino", no pigment ever
OCA2	OCA2 / P-gene	Present (normal enzyme)	Commonest type worldwide & in Africa; some pigment accrues with age	"Tyrosinase-positive", P-protein regulates melanosomal pH
OCA3	TYRP1 (tyrosinase-related protein-1)	Present	"Rufous/red albinism", reddish-brown skin & ginger hair	Seen in African populations
OCA4	SLC45A2 (MATP)	Reduced	Indistinguishable from OCA2 clinically; common in Japan	Membrane-associated transporter

High-yield: OCA1 = TYR gene = most severe and tyrosinase-NEGATIVE. OCA2 = P-gene = tyrosinase-POSITIVE and the commonest type globally. This single distinction is the most repeated MCQ in this topic.

OCA1 is further divided:

• OCA1A — total loss of tyrosinase. No pigment in skin, hair or eyes throughout life. Lifelong white hair, pink-white skin, translucent blue iris.
• OCA1B ("yellow/minimal-pigment" variant) — residual enzyme activity; some pigment develops over the years, hair may darken to yellow-blond.
• Temperature-sensitive variant — tyrosinase works only in cooler peripheral areas → pigmented hair on cooler limbs, white hair in warm axillae/scalp (analogous to the Siamese-cat coat pattern).

Inheritance & pathophysiology

All classic OCA types are autosomal recessive. Both parents are obligate unaffected carriers; recurrence risk per pregnancy is 25%.

• The visual abnormalities are NOT merely cosmetic. Melanin is essential for normal development of the retina and the optic pathways. Its absence in utero produces foveal hypoplasia and misrouting of optic nerve fibres — an excess of fibres decussate at the chiasm to the contralateral side. This misrouting is demonstrable on visual evoked potentials (VEP) and is virtually pathognomonic of albinism.
• Lack of melanin in the iris and retinal pigment epithelium causes iris transillumination and light scatter, producing photophobia and reduced acuity.

High-yield: Foveal hypoplasia + abnormal optic-fibre decussation (asymmetric VEP) is the ocular signature of albinism and explains why vision cannot be fully corrected with glasses.

Clinical features

Cutaneous / hair (the "oculo-cutaneous" component):

• White-to-cream hair; pink-white or creamy skin.
• Skin does NOT tan; instead it burns. Marked photosensitivity, sunburn, freckling and solar damage.
• Premature photoageing — solar elastosis, actinic keratoses.

Ocular (the most disabling component):

1. Reduced visual acuity (often 6/60 or worse) — does not fully correct with lenses because of foveal hypoplasia.
2. Nystagmus — pendular, horizontal, present from infancy; a frequent presenting sign.
3. Photophobia — from iris transillumination and lack of RPE pigment.
4. Iris translucency / transillumination — red reflex visible, "pink eyes".
5. Strabismus and reduced stereopsis (loss of binocular vision from fibre misrouting).
6. Refractive errors, hypopigmented fundus, hypoplastic fovea.

High-yield: Nystagmus in a hypopigmented infant = think albinism; the eye disease is the cause of disability, not the skin colour.

Syndromic albinism — the must-know associations

Two syndromes pair albinism with systemic disease and dominate NEET PG questions. Both involve defective biogenesis of lysosome-related organelles (melanosomes share machinery with platelet dense granules and lysosomes).

Hermansky–Pudlak syndrome (HPS)

• Tetrad: OCA + bleeding diathesis (platelet storage-pool deficiency — absent dense granules → defective aggregation despite normal platelet count) + ceroid-lipofuscin accumulation in tissues.
• Causes pulmonary fibrosis (often fatal in 4th–5th decade) and granulomatous colitis.
• Common in Puerto Rico. Gene HPS1 etc.
• Platelet count is normal; bleeding time prolonged, abnormal aggregometry, and electron microscopy shows absent dense bodies.

Chédiak–Higashi syndrome (CHS)

• OCA (partial, often silvery hair) + recurrent pyogenic infections + bleeding + progressive neurological decline.
• Defect in LYST (lysosomal trafficking regulator) → giant azurophilic granules in neutrophils and other leucocytes (the diagnostic hallmark on peripheral smear).
• NK-cell and neutrophil dysfunction — impaired chemotaxis and degranulation → severe infections (esp. Staphylococcus aureus).
• Most patients enter an "accelerated phase" — an HLH-like lymphohistiocytic infiltration, often EBV-driven, that is usually fatal.

Feature	Hermansky–Pudlak	Chédiak–Higashi
Gene	HPS1 (and others)	LYST
Hallmark cell finding	Absent platelet dense granules	Giant granules in leucocytes
Bleeding	Yes (storage-pool defect)	Yes
Infection / immune	No major immunodeficiency	NK + neutrophil dysfunction, recurrent infection
Organ-threatening	Pulmonary fibrosis, colitis	Accelerated phase (HLH-like), neuro decline
Population clue	Puerto Rico	—

High-yield: Giant lysosomal granules in neutrophils + partial albinism + recurrent infection + silvery hair = Chédiak–Higashi. Albinism + bleeding (no infection) + pulmonary fibrosis = Hermansky–Pudlak.

A third differential, Griscelli syndrome, also gives silvery-grey hair and (type 2) HLH/immune dysfunction but is distinguished by large clumped melanin in hair shafts on light microscopy and absence of giant granules in neutrophils.

Diagnosis & investigation of choice

Diagnosis is largely clinical (hypopigmentation + characteristic eye signs), supported by targeted tests.

Stepwise approach:

1. Clinical recognition → hypopigmented skin/hair + nystagmus + photophobia + iris transillumination.
2. Ophthalmological evaluation → slit-lamp iris transillumination, fundus (hypopigmented, foveal hypoplasia on OCT), and VEP showing the asymmetric/misrouted response — the single most specific functional test for albinism.
3. Light/electron microscopy of hair shaft → in Griscelli vs CHS differentiation.
4. Peripheral blood smear → giant granules (CHS); platelet aggregation studies & EM for dense granules (HPS).
5. Molecular genetic testing → confirms type (TYR, OCA2, TYRP1, SLC45A2, LYST, HPS genes); enables genetic counselling and prenatal diagnosis.
6. The historical hair-bulb tyrosinase incubation test (incubate plucked anagen hair in tyrosine/DOPA and look for pigment formation) separates OCA1 (negative) from OCA2 (positive) — still examined but largely superseded by genetics.

High-yield: Investigation of choice to confirm the diagnosis of albinism functionally = visual evoked potential (shows abnormal chiasmal decussation). Definitive aetiological diagnosis/type = molecular genetic testing.

Management & "drug of choice"

There is no cure and no drug that restores pigment. Management is preventive and supportive, centred on protecting skin and maximising vision.

Dermatological / oncological:

• Rigorous photoprotection is the cornerstone: broad-spectrum sunscreen (SPF ≥30, ideally ≥50), protective clothing, wide-brimmed hats, sun avoidance.
• Lifelong skin surveillance for premalignant and malignant lesions; early treatment of actinic keratoses.
• Education — this is the single most effective intervention to reduce skin-cancer mortality.

Ophthalmological:

• Refractive correction, tinted/photochromic lenses and dark glasses for photophobia.
• Low-vision aids, magnifiers; surgery for strabismus; nystagmus management.
• Regular paediatric and lifelong ophthalmology follow-up.

Syndromic:

• HPS → avoid antiplatelet drugs (aspirin/NSAIDs), use desmopressin/platelet transfusion for surgery/bleeds, screen and manage pulmonary fibrosis.
• CHS → aggressive infection control; haematopoietic stem cell transplantation is the only treatment that corrects the immune defect and prevents/treats the accelerated phase (though it does not reverse hypopigmentation or late neurological decline).
• Genetic counselling (25% recurrence risk) for all families.

High-yield: The "drug" of choice in OCA is sunscreen / photoprotection — the only intervention shown to alter the natural history (skin-cancer risk). HSCT is the definitive therapy in Chédiak–Higashi.

Complications

• Skin malignancy — the dominant long-term threat. Cumulative UV damage gives a markedly increased risk of squamous cell carcinoma (SCC), basal cell carcinoma and actinic keratoses; SCC is the commonest and most aggressive skin cancer in albinos, often appearing in young adults in sun-exposed sites. In equatorial regions skin cancer is a leading cause of premature death in people with albinism.
• Severe, permanent visual impairment; many are legally blind in terms of acuity though rarely totally blind.
• Psychosocial morbidity and social stigma, especially in parts of Africa where myths drive violence and discrimination.
• Syndromic complications: fatal pulmonary fibrosis/colitis (HPS), accelerated-phase HLH and neurodegeneration (CHS).

High-yield: Squamous cell carcinoma (not melanoma) is the leading cutaneous malignancy and a major cause of mortality in oculocutaneous albinism — paradoxically, melanoma risk is comparatively low because there is little melanocytic substrate, though amelanotic melanoma can occur and is easily missed.

Key differentials

Condition	Distinguishing feature
Vitiligo	Acquired, patchy depigmentation; melanocytes destroyed; normal eyes/vision; no nystagmus
Piebaldism	Autosomal dominant (c-KIT); congenital stable white forelock + ventral patches; absent melanocytes in patches; normal vision
Waardenburg syndrome	AD; white forelock + dystopia canthorum + heterochromia iridis + sensorineural deafness (PAX3)
Tuberous sclerosis (ash-leaf macules)	Hypopigmented (not depigmented) macules + seizures + adenoma sebaceum; not generalised
Phenylketonuria	Generalised hypopigmentation (fair hair/skin) due to ↓ tyrosine availability, plus intellectual disability + musty odour
Ocular albinism (OA1)	X-linked; eyes affected only, skin/hair near-normal; female carriers show "mud-splattered" fundus

High-yield: Differentiating OCA from ocular albinism — OA1 is X-linked recessive and confined to the eyes; OCA is autosomal recessive and affects skin, hair and eyes.

Recently asked / exam angle

• Gene–type matching is the favourite single-best-answer format: OCA1 → TYR (tyrosinase, most severe, tyrosinase-negative); OCA2 → P-gene (commonest, tyrosinase-positive); OCA3 → TYRP1 (rufous); OCA4 → SLC45A2/MATP.
• "Albinism + bleeding + pulmonary fibrosis" → Hermansky–Pudlak (platelet storage-pool defect).
• "Partial albinism + recurrent infection + giant granules in neutrophils + silvery hair" → Chédiak–Higashi (LYST), with NK-cell dysfunction and an accelerated phase; HSCT is curative for the immune defect.
• Investigation: VEP misrouting / hair-bulb tyrosinase test interpretation.
• Commonest malignancy in albinism asked as a one-liner → squamous cell carcinoma.
• Inheritance pattern (autosomal recessive) and recurrence risk (25%) — straightforward but frequently included.
• Image-based: peripheral smear with giant azurophilic granules (CHS) is a classic spotter.
• Distinguishing albinism (melanocytes present) from vitiligo/piebaldism (melanocytes absent) — concept question.

Mnemonics:

• "OCA1 is the worst, TYR comes first" → OCA1 = TYR gene = most severe.
• "Chédiak = Cells with giant granules; Hermansky = Haemorrhage + Honeycomb lung" → distinguishes the two syndromes.
• HPS clue: Puerto Rico + Pulmonary fibrosis + Platelet defect.

Rapid revision

1. Albinism = defective melanin synthesis with a normal number of melanocytes; autosomal recessive (recurrence risk 25%).
2. Central enzyme is tyrosinase (TYR); pathway: tyrosine → DOPA → dopaquinone → melanin.
3. OCA1 (TYR) = most severe, tyrosinase-negative; OCA1A = total absence of pigment for life.
4. OCA2 (P-gene) = commonest worldwide, tyrosinase-positive, pigment accrues with age.
5. OCA3 = TYRP1 (rufous/red albinism); OCA4 = SLC45A2/MATP.
6. Ocular hallmark = foveal hypoplasia + misrouted optic fibres → abnormal VEP, nystagmus, photophobia, low acuity not correctable by glasses.
7. Hermansky–Pudlak = albinism + platelet storage-pool bleeding + ceroid + pulmonary fibrosis; common in Puerto Rico.
8. Chédiak–Higashi = LYST defect, giant leucocyte granules, silvery hair, recurrent infection, NK-cell dysfunction, fatal accelerated phase; HSCT is curative for immune defect.
9. Squamous cell carcinoma is the leading malignancy and major cause of death; melanoma risk relatively low.
10. Cornerstone of management = photoprotection (sunscreen, clothing) + lifelong skin and eye surveillance; no cure.
11. Functional confirmatory test = VEP; aetiological confirmation = molecular genetics; historical hair-bulb tyrosinase test separates OCA1 (−) from OCA2 (+).
12. Ocular albinism (OA1) is X-linked and confined to the eyes — contrast with autosomal-recessive OCA affecting skin, hair and eyes.