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Anticipation & Sherman paradox
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Fragile X Syndrome is second only to Down Syndrome in causing congenital mental retardation and is the leading cause of inherited mental retardation. The disease is diagnosed by Polymerase Chain Reaction (PCR) on the X-chromosome(s) of affected individuals for a fragile area and the FMR1 gene. This fragile area generally results from a lack of folate, which causes triplet repeats in the fragile area of the X chromosome. The more triplet repeats there are on the X chromosome, the more severely affected the individual will be. An individual with less than 50 repeats generally will not be noticeably affected, while an individual with more than 200 repeats will be profoundly affected. In addition, anticipation is seen in the incidence of fragile X syndrome. Anticipation causes the disease to be more severe with each generation that is strikes. |
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| Click above to listen to a pronunciation of the disease. When prompted, click 'open from current location'! | ||
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The figure shown above is the x chromosome. The circled area shows the elongated, decondensed region at the tip of the long arm. This is the "fragile area." This picture was borrowed from Medical Genetics by Carey, John C., Jorde, Lynn B., and White, Raymond L and was modified using MS Paint v98 by Microsoft Corporation.
Click on the picture to see enlarged fragile regions.
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This page created by: Jennifer Butt