Fragile X syndrome is the most common form of inherited mental retardation in males and a significant cause in females. The inheritance is different from common dominant or recessive inheritance patterns. A fragile area on the X chromosome (called FMR1) has repeats in the genetic code. The more repeats, the more likely there is to be a problem. Boys and girls can both be affected, but because boys have only one X chromosome, a single fragile X is likely to affect them more severely.
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