Abnormal dystrophin expression in patients with limb girdle syndromes

Clinical differential diagnosis between Becker muscular dystrophy (BMD) and limb gridle muscular dystrophy (LGMD) may be difficult because the BMD clinical phenotype tends to overlap with other limb girdle syndromes, especially with LGMD. Therefore we studied the expression of dystrophin, the protein product of the Becker and Duchenne muscular dystrophy gene, in muscle biopsy specimens of 30 patients (18 males, of whom 15 represented spradic cases, and 12 females) diagnosed as having LGMD according to traditional clinical, electrophysiological and histological criteria. For dystrophin analysis, six different monoclonal antibodies directed against different epitopes of the dystrophin molecule were used. Immunocytochemically, five of the 30 LGMD patients (17%) showed abnormal dystrophin staining patterns diagnostic of BMD. Western blotting in these five patients, all sporadic cases, showed dystrophin of reduced size and/or abundance. Analysis of blood or muscle DNA using multiplex polymerase chain reaction revealed deletions in the dystrophin gene in three of the five. Thus, 5 of 15 (33%) sporadic male patients previously thought to have LGMD were identified as having BMD.