The cause of albinism is a mutation in one of several genes. Each of these genes provides the chemically coded instructions for making one of several proteins involved in the production of melanin. Melanin is produced by cells called melanocytes, which are found in your skin and eyes. A mutation may result in no melanin production at all or a significant decline in the amount of melanin.
In most types of albinism, a person must inherit two copies of a mutated gene — one from each parent — in order to have albinism (recessive inheritance). If a person has only one copy, then he or she won't have the disorder.
Impact of mutations on eye development
Regardless of which gene mutation is present, vision impairment is a common characteristic with all types of albinism. These impairments are caused by irregular development of the nerve pathways from the eye to the brain and from abnormal development of the retina.
Types of albinism
The system for classifying types of albinism is based primarily on which mutated gene caused the disorder rather than by outward signs. Nonetheless, most types of albinism have some features that distinguish them from each other. Types of albinism include:
Apr. 02, 2011
Oculocutaneous albinism. Oculocutaneous albinism is caused by a mutation in one of four genes. These mutations result in signs and symptoms related to vision (ocular) and those related to skin (cutaneous), hair and iris color.
Oculocutaneous albinism type 1 is caused by a mutation in a gene on chromosome 11. Most people with this type of albinism have milky white skin, white hair and blue eyes at birth. Some people with this disorder never experience changes in pigmentation, but others begin to produce melanin during childhood and adolescence. Their hair may become a golden blond or brown. Their skin usually doesn't change color, but it may tan somewhat. The irises may also change color and lose some of their translucence.
Oculocutaneous albinism type 2 is caused by a mutation in a gene on chromosome 15. It's more common in Sub-Saharan Africans, African-Americans and Native Americans than in other population groups. The hair may be yellow, auburn, ginger or red, the eyes can be blue-gray or tan, and the skin is white at birth. In people of African descent, the skin may be light brown, and in those of Asian or Northern European descent, the skin is usually white. In either case, the skin color is generally close to the family's coloring, but a little bit lighter. With sun exposure, the skin may over time develop freckles, moles or lentigines.
The rarer oculocutaneous albinism type 3 is caused by a gene mutation on chromosome 9 and has been primarily identified in black South Africans. People with this disorder usually have reddish-brown skin, ginger or reddish hair, and hazel or brown eyes.
Oculocutaneous albinism type 4, caused by a gene mutation on chromosome 5, is an uncommon form of the disorder generally presenting signs and symptoms similar to those of type 2. This type of albinism may be one of the most common forms among people of East Asian descent.
- X-linked ocular albinism. The cause of X-linked ocular albinism, which occurs almost exclusively in males, is a gene mutation on the X chromosome. People who have ocular albinism have the developmental and functional vision problems of albinism. But skin, hair and eye color are generally in the normal range or slightly lighter than that of others in the family.
- Hermansky-Pudlak syndrome. Hermansky-Pudlak syndrome is a rare albinism disorder caused by a mutation in one of at least eight genes associated with this syndrome. People with this disorder have signs and symptoms like those of oculocutaneous albinism, but they also develop lung and bowel diseases and a bleeding disorder.
- Chediak-Higashi syndrome. Chediak-Higashi syndrome is a rare form of albinism that's associated with a mutation in the LYST gene. Signs and symptoms are similar to those of oculocutaneous albinism. The hair is usually brown or blond with a silvery sheen, and the skin is usually creamy white to grayish. People with this syndrome have a defect with white blood cells that results in a susceptibility to infections.
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- Oculocutaneous albinism. Genetics Home Reference. http://ghr.nlm.nih.gov/condition/oculocutaneous-albinism/show/print. Accessed Feb. 21, 2011.