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Diseases

Genetic and Rare Diseases Information Center (GARD)

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Inheritance


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How is albinism inherited?

Different types of albinism can have different patterns of inheritance, depending on the genetic cause of the condition. Oculocutaneous albinism (OCA) involves the eyes, hair and skin. Ocular albinism (OA), which is much less common, involves primarily the eyes, while skin and hair may appear similar or slightly lighter than that of other family members.[1] Mutations in several different genes, on different chromosomes, can cause different types of albinism.

OCA is inherited in an autosomal recessive manner. This means that two mutations are necessary for an individual to have OCA. Individuals normally have two copies of each numbered chromosome and the genes on them – one inherited from the father, the other inherited from the mother. Neither of these gene copies is functional in people with albinism.[1] Each unaffected parent of an individual with an autosomal recessive condition carries one functional copy of the causative gene and one nonfunctional copy. They are referred to as carriers, and do not typically show signs or symptoms of the condition. Both parents must carry a defective OCA gene to have a child with albinism.[1] When two individuals who are carriers for the same autosomal recessive condition have children, with each pregnancy there is a 25% (1 in 4) risk for the child to have the condition, a 50% (1 in 2) risk for the child to be an unaffected carrier like each of the parents, and a 25% chance for the child to not have the condition and not be a carrier.

Ocular albinism type 1 is inherited in an X-linked pattern. A condition is considered X-linked if the mutated gene that causes the disorder is located on the X chromosome, one of the two sex chromosomes. In males (who have only one X chromosome and one Y), one altered copy of the causative gene in each cell is sufficient to cause the characteristic features of ocular albinism, because males do not have another X chromosome with a working copy of the gene. Because females have two copies of the X chromosome, women with only one copy of a mutation in each cell usually do not experience vision loss or other significant eye abnormalities. They may have mild changes in retinal pigmentation that can be detected during an eye examination.[2]

Researchers have also identified several other genes in which mutations can result in albinism with other features. One group of these includes at least eight genes (on different chromosomes) leading to Hermansky-Pudlak Syndrome (HPS). In addition to albinism, HPS is associated with bleeding problems and bruising. Some forms are also associated with lung and bowel disease.[1] Like OCA, HPS is inherited in an autosomal recessive manner.
Last updated: 4/10/2011

References
  1. What is Albinism?. NOAH. 2002; http://www.albinism.org/publications/what_is_albinism.html. Accessed 4/10/2011.
  2. Ocular Albinism. Genetics Home Reference. July 2007; http://ghr.nlm.nih.gov/condition/ocular-albinism. Accessed 4/10/2011.