Central nervous system involvements in Duchenne/Becker muscular dystrophy]

Duchenne/Becker muscular dystrophy (DMD/BMD) are the most common inherited muscular diseases caused by mutations in the dystrophin gene. The identification of novel dystrophins in the brain has recently implicated its absence or malfunction etiologically in mental retardation (MR). We therefore examined the relationship between molecular abnormalities and clinical phenotypes. Deletions of the dystrophin gene were analyzed in a total of 137 DMD/BMD patients (DMD 94, BMD 43) to determine central nervous system (CNS) symptoms. The mental capacity was assessed and patients with IQs below 70 were defined as mentally retarded. Thirty-nine percent of DMD boys and 12% of BMD patients were classified as mentally retarded. Eight DMD and 2 BMD patients were diagnosed as having autism. Forty-four percent of DMD and 79% of BMD patients had deletions in the dystrophin gene. All the DMD/BMD patients with deletions upstream of the 5' end of the gene were mentally normal. All of DMD/BMD patients with MR and/or autism had deletions containing the 3' end, although some patients with similar deletions were mentally normal. Our data suggest that Dp140, Dp71 and/or Dp116, the C-terminal translational products of dystrophin, may be related to MR and/or autism in DMD/BMD. However, there was an exception in our series. Three of eight sibling pairs in our cases had different phenotypes, although they had the same mutations in the dystrophin gene. Thus the CNS phenotypes were not determined by the mutations of dystrophin gene alone, and the interaction of dystrophin with other nuclear genes may play important roles.