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
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Reports outline experimental medicine study results from Tohoku University
2007 APR 17 -- A new study, "Neuroendocrine functions of melanocytes: beyond the skin-deep melanin maker," is now available. "The skin is armored with "dead cells", the stratum corneum, and is continuously exposed to external stressful environments, such as atmospheric oxygen, solar radiations, and thermal and chemical insults. Melanocytes of neural crest origin are located in the skin, eye, inner ear, and leptomeninges," investigators in Sendai, Japan report. "Melanin pigment in the skin is produced by melanocytes under the influence of various endogenous factors, derived from neighboring keratinocytes and underlying fibroblasts. The differentiation and functions of melanocytes are regulated at multiple processes, including transcription, RNA editing, melanin synthesis, and the transport of melanosomes to keratinocytes. Impairment at each step causes the pigmentary disorders in humans, with the historical example of oculocutaneous albinism. Moreover, heterozygous mutations in the gene coding for microphthalmia-associated transcription factor, a key regulator for melanocyte development, are associated with Waardenburg syndrome type 2, an auditory-pigmentary disorder. Sun tanning, melasma, aging spots (lentigo senilis), hair graying, and melanoma are well-known melanocyte-related pathologies. Melanocytes therefore have attracted much attention of many ladies, makeup artists and molecular biologists. More recently, we have shown that lipocalin-type prostaglandin D synthase (L-PGDS) is expressed in melanocytes but not in other skin cell types. L-PGDS generates prostaglandin D2 and also functions as an inter-cellular carrier protein for lipophilic ligands, such as bilirubin and thyroid hormones. Thus, melanocytes may exert hitherto unknown functions through L-PGDS and prostaglandin D2," wrote K. Takeda and colleagues, Tohoku University. The researchers concluded: "Here we update the neuroendocrine functions of melanocytes and discuss the possible involvement of melanocytes in the control of the central chemosensor that generates respiratory rhythm." Takeda and colleagues published their study in The Tohoku Journal of Experimental Medicine (Neuroendocrine functions of melanocytes: beyond the skin-deep melanin maker. The Tohoku Journal of Experimental Medicine, 2007;211(3):201-21). For additional information, contact K. Takeda, Tohoku University School of Medicine, Dept. of Molecular Biology and Applied Physiology, Sendai, Japan. The publisher of the The Tohoku Journal of Experimental Medicine can be contacted at: Tohoku University Medical Press, School of Medicine, Sendai, 980-77, Japan. Keywords: Japan, Sendai, Experimental Medicine. This article was prepared by Life Science Weekly editors from staff and other reports. Copyright 2007, Life Science Weekly via NewsRx.com.
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