Oculocutaneous Albinism
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What is oculocutaneous albinism?
Oculocutaneous albinism is a group of conditions that affect coloring (pigmentation) of the skin, hair, and eyes. Affected individuals typically have very fair skin and white or light-colored hair. They have an increased risk of skin damage and skin cancers, including melanoma, with sun exposure. 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); and increased sensitivity to light (photophobia).
The four types of oculocutaneous albinism are designated as type 1 (OCA1) through type 4 (OCA4). Oculocutaneous albinism type 1 is characterized by white hair, very pale skin, and light-colored irises. Type 2 is generally less severe than type 1; the skin is usually a creamy white color and hair may be light yellow, blond, or light brown. Type 3 includes a form of albinism called rufous oculocutaneous albinism, which usually affects dark-skinned people. Affected individuals have 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 with type 2. Because their features overlap, the four types of oculocutaneous albinism are most accurately distinguished by their genetic cause.
How common is oculocutaneous albinism?
Overall, an estimated 1 in 20,000 people worldwide are born with oculocutaneous albinism. The condition affects people in many ethnic groups and geographical regions. Types 1 and 2 are the most common forms of this condition; types 3 and 4 are less common. Type 2 occurs more frequently in African Americans, some Native American groups, and people from sub-Saharan Africa. Type 3 (rufous oculocutaneous albinism) has been described in people from southern Africa and Papua New Guinea. Studies suggest that type 4 occurs more frequently in the Japanese and Korean populations than in people from other parts of the world.
What genes are related to oculocutaneous albinism?
Mutations in the OCA2, SLC45A2, TYR, and TYRP1 genes cause oculocutaneous albinism.
Mutations in the MC1R gene modify the course of oculocutaneous albinism.
The four types of oculocutaneous albinism each result from mutations in a single gene: TYR, OCA2, TYRP1, or SLC45A2. Changes in the TYR gene cause type 1; mutations in the OCA2 gene are responsible for type 2; TYRP1 mutations cause type 3; and changes in the SLC45A2 gene result in type 4. These genes 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. Mutations in any of these genes disrupts 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, they typically have red hair instead of the usual yellow, blond, or light brown hair seen with this condition.
How do people inherit oculocutaneous albinism?
Each of the four types of oculocutaneous albinism is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder are carriers of one copy of the altered gene but do not show signs and symptoms of the disorder.
Source: National Institutes of Health
Studies from National Institutes of Health provide new data on hermansky-pudlak syndrome
2009 JUL 13 - (NewsRx.com) -- "Hermansky-Pudlak syndrome (HPS) is an autosomal recessive disorder characterized by oculocutaneous albinism, a bleeding disorder, and, in some patients, granulomatous colitis and/or a fatal pulmonary fibrosis. There are eight different subtypes of HPS, each due to mutations in one of eight different genes,whose functions are thought to involve intracellular vesicle formation and trafficking," scientists in the United States report. "HPS has been identified in patients of nearly all ethnic groups, though it has primarily been associated with patients Of Puerto Rican, Northern European, Japanese and Israeli descent. We report oil the diagnosis of HPS type I in two African-American patients. Both brothers carried compound heterozygous Mutations in HPS1: previously reported p.M32.5WfsX6 (c.972deIC) and a novel silent mutation p.E169E (c.507G > A), which resulted in a splice defect. HPS may be under-diagnosed in African-American patients and other ethnic groups. A history of easy bruising or evidence of a bleeding disorder, combined with some degree of hypopigmentation, should prompt investigation into the diagnosis of HPS," wrote M.A. Merideth and colleagues, National Institutes of Health. The researchers concluded: "Published 2009 Wiley-Liss, Inc." Merideth and colleagues published their study in American Journal of Medical Genetics Part a (Hermansky-Pudlak Syndrome in Two African-American Brothers. American Journal of Medical Genetics Part a, 2009;149A(5):987-992). For more information, contact M.A. Merideth, NHGRI, Sect Human Biochemistry Genetics, Medical Genetics Branch, National Institutes of Health, 10 Center Dr., MSC 1851, Bldg 10, Rm 10C-103, Bethesda, MD 20892, USA. Publisher contact information for the American Journal of Medical Genetics Part a is: Wiley-Liss, Division John Wiley & Sons Inc., 111 River St., Hoboken, NJ 07030, USA. Keywords: United States, Bethesda, Bleeding Disorder, Colitis, Crohn Disease, Dermatology, Fibrosis, Gastroenterology, Gastrointestinal, Granuloma, Hematology, Hepatology, Hermansky-Pudlak Syndrome, Oculocutaneous Albinism, National Institutes of Health. This article was prepared by Gastroenterology Week editors from staff and other reports. Copyright 2009, Gastroenterology Week via NewsRx.com.
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