What is albinism?

Causes and Symptoms

Albinism is a group of inherited conditions caused by alteration, or mutation, of one of the genes that affect normal pigment production. Mutation in any one of several genes involved in melanin production can produce individuals with less than the normal amounts of melanin. Lack of melanin can lead to many problems. When melanin is absent from the skin, the skin has no protection against ultraviolet (UV) light and burns easily in the sun. The skin cancer risk for albinos is quite high. Lack of melanin in the retina leads to lessened visual acuity. Albinism is classified into two main types, oculocutaneous albinism (OCA) and ocular albinism (OA). The former affects the skin, hair, and eyes, while the latter affects only the eyes.

One form of OCA is called tyrosinase-related OCA. It is an autosomal recessive characteristic; thus, affected individuals must inherit a mutated gene from both of their parents. The parents may themselves be albinos or, more usually, may be normal-appearing heterozygous carriers of this mutation. The enzyme coded by the normal gene, tyrosinase, converts tyrosine to dopa, the first step in the production of melanin. Most commonly, individuals with two copies of the mutated gene lack this enzyme and are unable to produce any melanin. These individuals exhibit classic albino traits, which may include pale, unpigmented skin and hair, pale blue/gray or even reddish irises, and severely decreased visual acuity. Less commonly, the mutation in the gene leads to lowered amounts of the enzyme, so that the affected person produces some melanin. The amount of melanin produced determines how severely affected the individual will be. These albinos have very little pigment at birth but accumulate more as they age.

Other autosomal recessive OCAs are caused by mutations in the P gene, TRP1 gene, Hermansky-Pudlak syndrome gene, and Chediak-Higashi syndrome gene. In all the above, some pigment is present at birth but individuals appear less pigmented when compared to siblings.

OA is an X-linked recessive disorder; therefore, it is more often seen in males. Skin, hair, and even iris color are in the normal range for the family, but examination shows a complete lack of pigment in the retina. Visual acuity is less than normal. Female heterozygous carriers show mosaicism, with some parts of the retina pigmented and other parts not.

Treatment and Therapy

Although no cure exists for albinism, some symptoms can be alleviated. Sunscreens of at least SPF 20 offer some protection from harmful UV radiation. Even with sunscreens, however, albinos should refrain from sun exposure between 10 a.m. and 3 p.m. Various types of eyeglasses can improve the vision of albinos, although visual acuity is rarely corrected completely. Albinos usually live a normal life span and have normal mental development.

Bibliography

A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M., Inc.; ©2005. Albinism; updated 2011 Nov 14; cited 2013 Aug 27; about 2 p.

A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M., Inc.; ©2005. Chediak-Higashi syndrome; updated 2011 Aug 4; cited 2013 Aug 27; about 2 p.

Levine, Norman, ed. Pigmentation and Pigmentary Disorders. Boca Raton, Fla.: CRC Press, 1993.

Nordlund, James J., et al., eds. The Pigmentary System: Physiology and Pathophysiology. 2d ed. New York: Oxford University Press, 2006.

Parker, Philip M., and James N. Parker. Albinism: A Medical Dictionary, Bibliography, and Annotated Research Guide to Internet References. San Diego, Calif.: Author, 2003.

Scriver, Charles R., et al., eds. The Metabolic and Molecular Bases of Inherited Disease. 8th ed. New York: McGraw-Hill, 2001.

Traboulsi, Elias I. Genetic Diseases of the Eye. New York: Oxford University Press, 2012.