• Muscle weakness, slowly progressive, causing
  • Difficulty with muscle skills (running, hopping, jumping)
  • Progressive difficulty walking
    • Ability to walk may continue into adulthood (up to age 40)
    • Frequent falls
  • problems breathing
• Cognitive dysfunction
• Skeletal deformities, chest and back (scoliosis)
• Muscle deformities
  • contractures of heels, legs
  • Pseudohypertrophy of calf muscles
• Fatigue
• Heart disease

The pattern of symptom development resembles that of Duchenne's muscular dystrophy, but with a much slower rate of progression. Muscle wasting begins in the legs and pelvis, then progresses to the muscles of the shoulders and neck, followed by loss of arm muscles and respiratory muscles. Calf muscle enlargement (pseudohypertrophy) is quite obvious. Cardiomyopathy may occur, but the development of congestive heart failure or arrhythmias (irregular heartbeats) is rare.

The ability to walk may continue to age 40 or older.

• A CPK may be elevated.
• An EMG (electromyography) shows that weakness is caused by destruction of muscle tissue rather than by damage to nerves.
• A muscle biopsy or genetic test (blood test) confirms the diagnosis.