There are nine forms of muscular dystrophy. The type of muscular dystrophy an individual is diagnosed with determines the severity of the symptoms and life expectancy, according to WebMD.
The most common form of muscular dystrophy in adults is myotonic muscular dystrophy, or MMD. Individuals with MMD have a decreased life expectancy. Duchenne muscular dystrophy is the most common form of muscular dystrophy in children and is only present in males. Boys with Duchenne MD usually die in their late teens or early 20s.
Congenital MD is present at birth or before age 2. Life expectancy for congenital MD ranges widely, with some individuals dying in infancy while others live into adulthood, says the National Institute of Neurological Disorders and Stroke.