Otherwise healthy 9-year-old African American boy seen for first time for complaints of frequent exhaustion, particularly when climbing stairs or walking for long periods. He could no longer participate in sports because of inability to keep up with his peers. He had been toe walking and had become clumsier over the past year, tripping and falling more frequently. Besides a mild delay in walking (around 16 months), his mother had reported no outstanding gross motor delays in infancy. He was in a regular class in school, although he did receive extra help in math and reading.
He had hypertrophic calf muscles and significant thigh muscle wasting. Gait was abnormal and unsteady, with mild weakness noted bilaterally in the lower extremities. Deep tendon reflexes were normal, and cranial nerves II through XII were intact. The remainder of the physical findings were unremarkable.
Blood tests revealed an extremely elevated creatine phosphokinase (CPK) level (17,863 IU/L [normal, less than 160 IU/L]) and elevated liver transaminase levels (aspartate aminotransferase [AST], 382 U/L; and alanine aminotransferase [ALT], 682 U/L).
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