Duchenne muscular dystrophy is a recessive X-linked form of muscular dystrophy leading to rapid progression of muscle degeneration. It is the most common and severe form of muscular dystrophy. The affected gene is the dystrophin gene on the X chromosome (Xp21); dystrophin protein is an important muscle structural protein, and mutation results in a virtual absence of the dystrophin protein.
Affected boys are normal at birth but have onset of symptoms by age 5. Clinical features include:
• Progressive muscular weakness
• Calf pseudohypertrophy
• Proximal weakness of shoulder and pelvic girdles
• Possible heart failure and arrhythmias
• Respiratory insufficiency and pulmonary infections as a sult of decreased mucociliary clearance
Lab studies show elevated serum creatine kinase. Muscle biopsy shows muscle fibers of various sizes; necrosis, degeneration, and regeneration of fibers; fibrosis; and fatty infiltration. Immunostains show decreased dystrophin protein. Diagnosis can also be confirmed with genetic testing.
Becker muscular dystrophy is a recessive X-linked inherited disorder leading to slowly progressive muscle weakness of the legs and pelvis.
• Less severe than Duchenne
• Not as common as Duchenne as a later onset than Duchenne, with variable progression
• Mutation produces an altered dystrophin protein
• Cardiac involvement is rare, and patients can have relatively normal lifespan