Recessive Gene For Ocular Albinism example essay topic

In the past, Albinism Albinism In the past, albinos were usually treated with fear or awe. They were sometimes killed at birth. Albino births were common enough in some groups not to cause any excitement. For example, among the San Blas Indians of Panama, one in approximately 130 births is an albino. In the mid-nineteenth century, albinos were exhibited in sideshows. Whole families were displayed at times and were described as a unique race of might people.

They were said to live underground and to come out only at night when the light was dim and would not hurt their eyes. Albinism is a genetic defect if the integumentary system. Albinism occurs when the body fails to produce melanin. Melanin forms in a special cell called the melanocyte. This cell is found in the skin, in the hair follicle, and in the iris and retina of the eye. There are many steps in converting the amino acid tyrosine to melanin pigment.

Two types of melanin form: black-brown eumelanin and red-blood pheomelanin. Trosiase is the major enzyme involved in the formation of melanin pigment. Tyrosinase is responsible for converting tyrosine to DOPA and on to dopaguinone. The dopaguinone then forms black-brown eumelanin or red-yellow pheomelanin. The tyrosinase enzyme is made by the tyrosinase gene on chromosome 11, and alterations of this gene can produce on type of albinism because the tyrosinase enzyme made by the altered gene does not work correctly. Two additional enzymes called tyrosinasa-related protein 1 or DHICA oxidase and tyrosinase-related protein 2 or dopachrome tautomerase are important in the formation of eumelanin pigment.

The gene for DHICA oxidase in on chromosome 9 and the gene for dopachrome tautomerase in on chromosome 9. Alterations of the DHICA oxidase gene are associated with a loss of function of this enzyme and this causes one type of albinism. An alteration of the gene for dopachrome tautomerase does not produce albinism. Three other genes make proteins that are also involved in melanin pigment formation and albinism, but the exact role of these proteins remains unknown.

These genes are the P gene on chromosome 15, the Hermansky– Pudlak syndrome gene on chromosome 10, and the ocular albinism gene on the X chromosome. The gene carrying the defect that produces albinism is recessive, which means that both parents must carry this recessive gene in order to produce a child with the condition. When both parents carry the gene (and neither has albinism), there is a one in four chance with each pregnancy that their child will have albinism. The inheritance pattern of ocular albinism is alittle different. This condition is X-linked, meaning that the recessive gene for ocular albinism is located on the X chromosome. X-linked ocular albinism appears just about only in males who inherit the condition from their mothers.

Albinism is a recessive inherited defect in melanin metabolism in which pigment is absent from the hair, skin, and eyes (oculocutaneous albinism) or just from the eyes (ocular Albinism). Albinos tend to be children of parents who were first cousins. For a long time, the term "albinism' referred only to people who had white hair, white skin, and blue eyes. Individuals who had OCA and pigmented hair and eyes were identified, particularly in the African and African-American population, and terms such as ' incomplete albinism', ' partial albinism' of ' imperfect albinism' were used for this, but these terms are inappropriate and are no longer used. In the 1960's, Dr. Carl Witkop invented the hairbulb incubation test to separate pigmenting and non-pigmenting types of OCA and stared to use the terms "ty-neg' or "tyrosinase-negative' and "ty-pos' or "tyrosinase-positive' OCA. Freshly plucked hairbulbs from a person with OCA were place in a solution of tyrosine or dopa in a test tube and watched to see if pigment formed in the cells in the hairbulb.

If no pigment formed, the test was positive and the diagnosis was ty-pos OCA. Although this simple test showed that there were different types OCA, further studies have shown that the hairbulb incubation test is not very sensitive and has many false negative and false positive responses. As a result, the hairbulb incubation test is no longer used in the evaluation of and individual with OCA. In the 1980's the classification of OCA was expanded using very careful skin, hair, and eye examinations.

The reason for this was the knowledge that there were more than 50 gene loci that controlled pigmentation in the mouse, and it was suggested that careful studying of the skin, hair, and pigmentation of individuals with OCA could help identify the human equivalent of each of these genes. A number of types of OCA were identified, including platinum OCA, minimal pigment OCA, yellow OCA, temperature-sensitive OCA, autosomal recessive ocular albinism and brown OCA, and it was hoped that each would be caused by a different gene. In the 1990's, we were able to identify the genes involve in most types of OCA, and have found that the classifications based on hair, skin and eye color is not accurate and that it was better to classify OCA types based on the specific gene involved. People who have oculocutaneous albinism are unable to produce melanin; they have white, yellow, or yellow-brown hair, very light eyes (usually blue or grayish rather than pink), and very fair skin. It is a common notion that people with albinism must have red eyes, but in fact the color of the iris varies from a dull gray to blue to brown. Under certain lighting conditions, little pigment is visible.

This reddish reflection comes from the retina, which is the surface lining the inside of the eye. This reddish reflection is similar to that which occurs when a flash photograph is taken of a person looking right at the camera, and the eyes appear red. With some types of albinism the red color can reflect back through the iris as well as through the pupil. The fovea is a small but most important area of the retina in the inside of the eye. The retina contains the verve cells that detect the light entering the eye and transmit the signal for the brain. The fovea is the are of the retina that allows sharp vision, such as reading, and this area of the retina does not develop in albinism.

Scientist do not know why the fovea does not develop normally with albinism, but it is relate to the lack of melanin pigment in the retina during development of the eye. The developing eye seems to need melanin for organizing the fovea. The major abnormality of the eye in albinism involves the development of the nerves that connect the retina to the brain. People with albinism have and unusual patterns for sending nerve signals from the eye to the brain. The nerve connections from the eye to the vision areas of the brain are organized differently from the normal. This unusual pattern for nerve signals probably prevents the eyes from working normally together, and causes reduced depth perception.

Strabismus is also common in albinism and is relate to the altered development of the optic nerves. The strabismus in albinism is usually not severe and tends to alternate between the right and left eye. Nystagmus, is an involuntary movement of the eyes back and forth. Many people with albinism learn to use a head tilt or turn that decreases the movement and may even improve their vision.

Photophobia (Sensitivity to light) occurs when the iris allows "stray' light to enter the eye and cause sensitivity. Contrary to common idea, this sensitivity does not limit people with albinism from going out into the sunlight. People with albinism are not 'blind', but their vision is not normal, and cannot be corrected completely with glasses. Extreme far-sightedness or near-sightedness, and astigmatism are common acuity ranges from 20/20 to 20/400.

Normal or near-normal vision is unusual, however, even when glasses are worn. Ophthalmologists and optometrists can help people with albinism compensate for their eye problems, but they cannot cure them. For help with visual activity, eye doctors experienced in low vision can prescribe a variety of devices. Glasses may be the only thing that is needed, but some may need bifocal glasses with a strong reading correction may serve well for many people with albinism. For nystagmus, research has searched for an effective treatment that helps in contact lenses, and surgery. The most promising may be eye muscle surgery that reduces the movement of the eyes.

Most people with albinism do not tan, and they burn easily when exposed to the sun. People with albinism who develop increasing amounts of hair and skin pigment as they grow older may not be bothered by the sun, and may tan with sum exposure. If sun exposure produces a sunburn, then the skin must be protected to prevent burning and damage. Sunscreen may aid in protection from the sun but it is not a cure. Albinos usually wear sunglasses or tented glasses to protect their eyes from the ultraviolet rays from the sun.

Albinism may cause social problems, because people with albinism look different from their families, peers, and other members of their ethnic group. Growth and development of a child with albinism should be normal and intellectual development is normal. Developmental milestones should be achieved at the normal age. General health of a child and an adult with albinism is normal, and the reduction in melanin pigment in the skin, hair, and the eyes should have no effect on the brain, the cardiovascular system, the lungs, the gastrointestinal tract, the genitourinary system, the musculoskeletal system, or the immune system. The expected life span of an albino is normal. Albinism In the past, albinos were usually treated with fear or awe.

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