Albinism
Albinism refers to a group of inherited conditions that results in little or no pigment, a matter which gives the skin, hair, and eyes their color. The primary role of this pigment, called melanin, is to protect the skin from sun damage by absorbing ultraviolet (UV) rays. Albinism, found in people of all races, is caused by a defective gene passed on from either parent. Parents of people with albinism usually do not have the condition. Approximately one in 17,000 people are born with albinism.
For years, it was assumed that only people born with milky-white skin, pure white hair, and pale blue eyes had albinism. Researchers now know there are many different manifestations of albinism, classified into two primary categories: Oculocutaneous albinism (OCA), of which there are 10 subcategories, means there is little or no pigment in the skin, hair, and eyes. Ocular albinism (OA), with five subcategories, means the pigment is missing primarily from the eyes. With continuing research, more specific classifications are expected.
In the 1960s, Dr. Carl Witkop developed a hair bulb incubation test to differentiate between two types of OCA-- tyrosinase-negative (ty-neg), in which no pigment is produced and difficulty with vision is increased, and tyrosinase-positive (ty-pos), in which small amounts of pigmentation and less severe visual difficulties occur. Tyrosinase, an enzyme involved in changing tyrosine, an amino acid, into melanin, is formed by the tyrosinase gene on chromosome 11. Alteration of this gene adversely affects tyrosinase production and is classified as ty-neg albinism. The genetic defect causing other types of albinism is not as clear, although mutation of the gene for tyrosinase-related protein 1 (or DHICA oxidase) production, found on chromosome 9, results in loss of function of this enzyme and produces one type of albinism.
The hair bulb test produced many false negative and false positive results. In the 1980s, researchers stopped using this test and began carefully examining skin, hair and eyes to help classify albinism. These attempts were also often inaccurate. In the 1990s, scientists began identifying specific genes associated albinism. So far, five genes are know to be associated with the development of OCA, and one with OA.
People with albinism can expect to live normal, productive life spans, and the increased risk of skin cancers due to the lack of protection afforded by melanin need not prevent them from enjoying outdoor activities. However, sun blocks with a protection factor of 20 or more and protective clothing should be used, particularly in tropical locations and higher altitudes where UV rays are more intense; while skiing or swimming because snow, sand, and water reflect the sun's rays; and during the summer solstice, particularly between 10 a.m. and 2 p.m. standard time.
Visual disorders associated with albinism—including nystagmus (fast, irregular movement of the eyes back and forth), strabismus (cross-eyed or lazy eye), sensitivity to bright light; and either far- or near-sightedness--cannot be cured but can be alleviated with optical aids recommended by experienced ophthalmologists.
This is the complete article, containing 487 words
(approx. 2 pages at 300 words per page).
