What causes myotonic dystrophy?
Myotonic dystrophy can occur in both sexes and is the most common form of adult muscular dystrophy, with symptoms often starting in adolescence. Myotonic dystrophy is caused by an inherited gene defect, called a “triple repeat,” on chromosome 19. The defective gene has not been positively identified as of early 1998. The triple repeat probably affects neighboring genes as well. Involvement of more than one gene would explain the multisystem effects of DM. The gene is inherited in an autosomal dominant pattern. In this pattern, one copy of the gene inherited from an affected parent is enough to cause the disease in the offspring. The chance of inheriting the DM gene from an affected parent is 50% for each child. This percentage is not changed by results of other pregnancies. The relation between the affected gene and the resulting myotonia, or inability to relax muscles, is not yet understood. The disease somehow blocks the flow of electrical impulses across the muscle membrane. Without
