Oculocutaneous albinism type 1

Overview

A rare inherited disorder characterized by complete lack of pigmentation in the skin, eyes and hair. Type 1A involves a complete absence of tyrosinase which is needed for the production of melanin which gives the skin, hair and eyes their color - type B involves only a partial absence of tyrosinase. It is caused by mutations in the TYR gene

Symptoms

* White hair * Very pale skin * Light-colored irises * Reduced pigmentation in iris * Reduced retinal pigmentation

Causes

Oculocutaneous albinism results from autosomal recessive inheritance; ocular albinism, from an X-linked recessive trait that causes hypopigmentation only in the iris and the ocular fundus. Normally, melanocytes synthesize melanin. Melanosomes, melanin-containing granules within melanocytes, diffuse and absorb the sun's ultraviolet light, thus protecting the skin and eyes from its dangerous effects. In tyrosinase-negative albinism (the most common type), melanosomes don't contain melanin because they lack tyrosinase, the enzyme that stimulates melanin production. In tyrosinase-positive albinism, melanosomes contain tyrosine, a tyrosinase substrate, but a defect in the tyrosine transport system impairs melanin production. In tyrosinase-variable albinism (rare), an unidentified enzyme defect probably impairs synthesis of a melanin precursor. Other rare forms of albinism are Ch├ędiak-Higashi syndrome (tyrosine-negative albinism with hematologic and neurologic manifestations); Hermansky-Pudlak syndrome (tyrosinase-positive albinism with platelet dysfunction, bleeding abnormalities, and ceroidlike inclusions in many organs); and Cross-McKusick-Breen syndrome (tyrosinase-positive albinism with neurologic involvement). In the United States, both types of albinism are more common in Blacks than in Whites. Native Americans have a high incidence of the tyrosine-positive form.

Diagnosis

Diagnosis is based on clinical observation and the patient's family history. Microscopic examination of the skin and of hair follicles determines the amount of pigment present. Testing plucked hair roots for pigmentation when incubated in tyrosine distinguishes tyrosinase-negative albinism from tyrosinase-positive albinism. Tyrosinase-positive hair bulbs will develop color.