Muscular dystrophy (MD) is an inherited muscle disorder with an unknown cause. Only males are affected, and only females can pass on the MD gene. MD involves slow but progressive degeneration of muscle fibers. Duchenne muscular dystrophy (DMD) is the most common type of MD. DMD is rarely diagnosed before age 3 but progresses rapidly. By age 8-10, affected children are no longer able to walk. There is no known cure for MD; however, for unknown reasons corticosteroids, such as prednisone, delay the loss of muscle function. If your child has DMD, you are probably aware of the use of deflazacort--it has been standard treatment for DMD for more than a decade.