Oculocutaneous albinism

Definition

Oculocutaneous albinism (OCA) is a group of rare inherited disorders of melanin formation. Melanocyte numbers are normal, but melanin production is absent or greatly reduced, so the skin, hair and eyes are diffusely hypopigmented. In ocular albinism, by contrast, mainly the eyes are affected.

Classification

Eight genetic forms are known, of which the first four are well characterised; OCA1 and OCA2 are the most common.

• OCA1A (TYR, absent tyrosinase activity): milky-white skin and hair, blue-grey eyes, most severe visual impairment; naevi are non-pigmented.
• OCA1B (reduced tyrosinase activity): variable dilution of pigment.
• OCA2 (OCA2 gene): minimal to moderate pigment dilution, lentigines on sun-exposed skin; the most common form in Africa.
• OCA3 (TYRP1): brown skin, reddish hair; only in people with otherwise dark skin.
• OCA4 (SLC45A2): similar to OCA2.

Occurrence & epidemiology

OCA occurs worldwide in people of all ethnic backgrounds. Inheritance is mostly autosomal recessive; autosomal dominant forms are rare. About 1 in 70 people carries an albinism gene; if both parents are carriers, the risk of an affected child is 1 in 4.

Clinical features

• Skin: very fair and highly prone to sunburn; markedly increased risk of skin cancer, mainly squamous and basal cell carcinomas, which are often barely pigmented.
• Hair: white to very light.
• Eyes: iris translucency, reduced retinal pigmentation, foveal hypoplasia and misrouted optic nerve fibres at the chiasm; resulting in photophobia, nystagmus, strabismus and reduced visual acuity.

Diagnosis

• Diagnosis is based on the skin and eye findings; an ophthalmological examination is required (iris translucency, retinal pigment, foveal hypoplasia, nystagmus).
• As the subtypes cannot always be distinguished clinically, genetic testing may be helpful.

Differential diagnoses

• Vitiligo
• Piebaldism
• Tuberous sclerosis
• Hypomelanosis of Ito (incontinentia pigmenti achromians)
• Naevus depigmentosus (achromic naevus)
• Xeroderma pigmentosum (XP)

Keep learning in the app

References (selection)

1. DermNet: Albinism
2. MSD Manual Professional: Albinism

Cross-references