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摘要

Muscular dystrophies are a group of diseases that are caused by a genetic mutation (a change in genetic material that can be passed on to children), affect muscles, and are progressive (increase in severity over time). The most common types are Duchenne muscular dystrophy, the most common childhood form of muscular dystrophy. It is an X-linked disease, which means that the gene is passed from mothers to their sons. Becker muscular dystrophy, with a genetic defect very similar to that in Duchenne muscular dystrophy, but not as severe.Together, Duchenne and Becker muscular dystrophies affect 1 to 2 in 10 000 males between the ages of 5 and 24 years. Myotonic dystrophy. Patients have myotonia (delayed relaxation of muscles after contraction), for example, after grasping a doorknob. There are several different types within this group. They occur in both men and women and affect about 1 in 8000 people. The December 14, 2011, issue of JAMA includes an article about myotonic muscular dystrophy.