A newborn is noted to have white hair, pinkish-white skin, blue-grey irises, and marked photophobia with nystagmus. The hair bulb tyrosinase test shows no pigment formation. What is the underlying genetic defect?

• A Mutation in the P gene on chromosome 15
• B Dominant mutation in the KIT proto-oncogene
• C X-linked mutation in the OA1 gene at Xp22
• D Autosomal recessive mutation encoding the tyrosinase enzyme ✓

Explanation

Oculocutaneous albinism type 1A results from autosomal recessive mutations in the tyrosinase gene (TYR) causing complete absence of tyrosinase activity, so no melanin is produced in skin, hair, and eyes, giving nystagmus, photophobia, and reduced visual acuity. Option A describes OCA type 2, which retains some pigment production and shows a positive hair bulb test. Option C is ocular albinism type 1, which affects mainly the eyes with normally pigmented skin.

Reference: Fitzpatrick's Dermatology, 9th ed.

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