The Duchenne and Becker muscular dystrophies are inherited as X-linked, recessive traits, meaning that only males inherit the condition. Duchenne muscular dystrophy is the most common form of muscular dystrophy. The age of onset is between one and five years of age and affects 1 in every 3,500 males. Progressive muscle weakness continues rapidly, and by 12 years of age affected individuals are typically confined to wheelchairs. Death usually occurs by the age of 20 due to respiratory infection or cardiac failure. The age of onset of Becker muscular dystrophy is between 5 and 25 years, has a slow progression with milder symptoms, and some individuals do have a normal life span.