Albinism

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Albinism

Definition:

Albinism is a defect of melanin production. This defect results in the partial or full absence of pigment from the skin, hair, and eyes.

Alternative Names:
Hypopigmentation; Oculocutaneous albinism; Ocular albinism
Causes, incidence, and risk factors:

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Albinism results when the body is unable to produce or distribute pigment, called melanin, because of one of several possible genetic defects. In Type 1 albinism defects in the metabolism of tyrosine lead to failure in converting this amino acid to melanin. This is due to a genetic defect in tyrosinase -- the enzyme responsible for metabolizing tyrosine.

Type 2 albinism is due to a defect in the "P" gene. Those with this type have slight pigmentation at birth.

In the most severe form of albinism (called oculocutaneous albinism), those affected appear to have hair, skin, and iris color that are white or pink as well as vision defects. This is inherited via an autosomal recessive process.

Albinism of just the eyes also occurs. This is called ocular albinism and can be inherited via either an X-linked or an autosomal recessive process. In this form of albinism, skin color is usually normal and eye color may be in the normal range. However, examination of the eye will show that there is no pigment in the retina.

Hermansky-Pudlak syndrome is a form of albinism that is associated with a bleeding disorder as well as lung and bowel diseases. If a person with albinism has unusual bruising or bleeding, this syndrome should be considered.

Other complex diseases may be associated with localized albinism (loss of pigment in only a specific area). These include:

Waardenberg syndrome (often a white forelock -- a lock of hair that grows on the forehead, or absence of pigment in one or both irises)
Chediak-Higashi syndrome (diffuse but not complete depigmentation of skin)
Tuberous sclerosis (white leaf macule) -- small localized areas of depigmentation)