Genetic abnormalities in Duchenne and Becker dystrophies: clinical correlations

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are two allelic forms of an X-linked muscle disorder exhibiting phenotypic heterogeneity. We studied 49 individuals clinically diagnosed as having classic DMD, female DMD, mild DMD "outliers," and BMD. The patients' DNA was analyzed and alterations detected were correlated with particular phenotypes. We found that 14 of 32 classic DMD patients have an internal deletion in the same, relatively small, region of the gene; therefore this region may undergo deletions at a higher rate than the remainder of the gene. We could detect no alterations in the DNA in the remaining 18 patients. Selected patients from both groups failed to show muscle dystrophin. Seven of 11 patients with a mild DMD or BMD phenotype showed deletions at the 5' end of the gene. The other 4 patients failed to show deletions. Three of the patients with both a mild phenotype and a deletion at the 5' end had normal or low amounts of a dystrophin of smaller molecular weight. Patients with classic DMD who had a detectable deletion had a milder clinical course than those without. Contrary to a previous report, no patient in the population of clinically precisely defined DMD boys showed a deletion at the 5' end; thus, the outlier and BMD patients may be genetically different from boys with classic DMD. This correlation may be of diagnostic and prognostic significance.