Muscular dystrophy is a group of inherited disorders characterized by the degeneration of muscle fibers. Muscle bundles are replaced by other types of tissue, e.g. adipose (fat) or fibrous tissues. The most common form is Duchenne muscular dystrophy. There is a wide variety of characteristics depending on the type of inheritance, age of onset and the muscles affected. the mode of inheritance: could be x-linked recessive (transmitted by females, and manifested only in males), autosomal dominant, autosomal recessive age of onset: ranges from infancy to 60 years old muscles affected: could be the pelvic, muscles, facial and shoulder muscles, or may be limited to only the extraocular muscles, cardiac muscles may be affected.