Muscular dystrophy is caused by defects in certain genes, with type determined by the abnormal gene. In 1986, researchers discovered the gene that, when defective or flawed, causes Duchenne muscular dystrophy. In 1987, the muscle protein associated with this gene was named dystrophin. Duchenne muscular dystrophy occurs when that gene fails to make dystrophin. Becker muscular dystrophy occurs when a different mutation in the same gene results in some dystrophin, but it's either not enough or it's poor in quality. Scientists have discovered and continue to search for the genetic defects that cause other forms of muscular dystrophy.
Most of the muscular dystrophies are a form of inherited disease called X-linked disorders or genetic diseases that mothers can transmit to their sons even though the mothers themselves are unaffected by the disease.
Men carry one X chromosome and one Y chromosome. Females carry two X chromosomes. Thus, in order for a girl to become affected by muscular dystrophy, both of her X chromosomes would have to carry the defective gene -- an extremely rare occurrence, since her mother would have to be a carrier (one defective X chromosome) and her father would have to have muscular dystrophy (since men carry just one X chromosome, the other is a Y chromosome).
A female who carries the defective X chromosome can pass the disease to her son (whose other chromosome is a Y, from the father).
A few muscular dystrophies aren't inherited at all and occur because of a new gene abnormality or mutation.
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