Albinism

Albinism is an inherited disorder that results from a defect in melanin metabolism of the skin and eyes (oculocutaneous albinism) or just the eyes (ocular albinism). Ocular albinism impairs visual acuity. Oculocutaneous albinism also causes severe intolerance to sunlight and heightens susceptibility to skin cancer in exposed areas.

Causes

Oculocutaneous albinism results from an autosomal recessive trait; ocular albinism results from an X-linked recessive trait that causes hypopigmentation only in the iris and the ocular fundus.

Normally, melanocytes (pigment cells) 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 oculocutaneous albinism (most common), melanosomes don't contain melanin because they lack tyrosinase, the enzyme that stimulates melanin production. In tyrosinase-positive oculocutaneous 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.

Tyrosinase-negative albinism affects about 1 in every 34,000 persons in the United States and strikes whites and blacks equally. Tyrosinase-positive albinism strikes more blacks than whites. Native Americans have a high incidence of both forms.

Symptoms

• Extremely light skin color.
• Light or white coloured hair.
• Light eye color, sometimes appearing pink.
• High susceptibility to sunburn and skin cancer.
• Vision problems.

Diagnostic tests

Microscopic examination of the skin and of hair follicles is used to determine the amount of pigment present. Pigmentation testing of plucked hair roots by incubating them in tyrosinase distinguishes tyrosinase­negative albinism from tyrosinase-positive albinism. Tyrosinase-positive hair bulbs develop color.

Treatment

There is no cure or treatment for albinism. Since individuals with albinism have little or no melanin in their skin, they need to use a broad-spectrum sunscreen and wear adequate clothing when outside to prevent ultraviolet-induced damage to the skin. The use of sunglasses will reduce the symptoms of light sensitivity as well as protecting the eyes. An ophthalmologist can treat other eye or vision symptoms. Individuals with albinism should see a dermatologist regularly to be screened for skin cancer. Albinism does not alter life expectancy or have other serious health effects.

Prevention

As this is a large group of inherited conditions genetic counseling is important. Genetic counseling should be considered for individuals with a family history of albinism or hypopigmentation.

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