Unusual expression and very mild course of Xp21 muscular dystrophy (Becker type) in a 60-year-old man with 26 percent deletion of the dystrophin gene.

A 54-year-old farmer with a negative family history had had mild proximal weakness for the previous 4 years. Clinical examination showed marked scoliosis, barrel-shaped chest, diffuse hypotrophy, and mild proximal weakness. Creatine kinase was 938 U/l; electrocardiography and echocardiography were normal. EMG disclosed myopathic changes. Muscle biopsy showed slight, nonspecific alterations. Dystrophin was present and normally distributed with antibodies against the C-terminal and N-terminal, whereas it was not recognized by the antibody against the rod domain. Western blotting detected an abnormal molecular weight protein of 320 kd (normal, 427 kd). Southern blot analysis revealed a deletion from exon 21 to exon 44, corresponding to 26% of the coding region of dystrophin. Six years' follow-up did not disclose progression of the muscle disease.