Oculocutaneous albinism

Oculocutaneous albinism is a group of conditions that affect the color of (pigmentation) of the skin, hair, and eyes. Affected individuals typically have very fair skin and white or light-colored hair. Long-term sun exposure greatly increases the risk of skin damage and skin cancers, including an aggressive form of skin cancer called melanoma, in people with this condition. 

Oculocutaneous albinism also reduces pigmentation of the colored part of the eye (the iris) and the light-sensitive tissue at the back of the eye (the retina). People with this condition usually have vision problems such as reduced sharpness; rapid, involuntary eye movements (nystagmus); eyes that do not point in the same direction (strabismus); and increased sensitivity to light (photophobia).

Researchers have identified multiple types of oculocutaneous albinism, which are distinguished by their specific skin, hair, and eye color changes, and by their genetic cause. Oculocutaneous albinism type 1 is characterized by white hair, very pale skin, and light-colored irises. Type 2 is typically less severe than type 1; the skin is usually pale and hair may be light yellow, blond, or light brown. Type 3 causes reddish-brown skin, ginger or red hair, and hazel or brown irises. Type 3 is often associated with milder vision abnormalities than the other forms of oculocutaneous albinism. Type 4 has signs and symptoms similar to those seen in people with type 2.

There are several additional, rare types of oculocutaneous albinism.

While the prevalence of oculocutaneous albinism varies by type and country, it is estimated that this condition affects 1 in 4,000 to 7,000 people in African populations and 1 in 12,000 to 15,000 people in European populations. Some isolated communities have higher occurrences of oculocutaneous albinism than their neighboring areas. Prevalence information for other populations is difficult to estimate, but oculocutaneous albinism affects people in all regions of the world.

Oculocutaneous albinism can result from variants (also known as mutations) in several genes, including TYR, OCA2, TYRP1, and SLC45A2. Variants in the TYR gene cause type 1, variants in the OCA2 gene cause type 2, variants in the TYRP1 gene cause type 3, and variants in the SLC45A2 gene cause type 4. Variants in additional genes likely underlie the other forms of this disorder. The genes associated with oculocutaneous albinism are involved in producing a pigment called melanin, which is the substance that gives skin, hair, and eyes their color. In the retina, melanin also plays a role in normal vision. Variants in any of these genes disrupt the ability of cells to make melanin, which reduces pigmentation in the skin, hair, and eyes. A lack of melanin in the retina leads to the vision problems characteristic of oculocutaneous albinism.

Alterations in the MC1R gene can change the appearance of people with oculocutaneous albinism type 2. This gene helps regulate melanin production and is responsible for some normal variation in pigmentation. People with genetic changes in both the OCA2 and MC1R genes have many of the usual features of oculocutaneous albinism type 2, including light-colored eyes and vision problems. However, these individuals typically have red hair instead of the usual yellow, blond, or light brown hair seen in people with this condition.

Some individuals with oculocutaneous albinism do not have variants in any of the known associated genes. In these people, the genetic cause of the condition is unknown.

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell must have a variant to cause the disorder. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition.