Background: Carriers of Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) may show muscle weakness or dilated cardiomyopathy. Studies focusing on skeletal-muscle involvement were done before DNA analysis was possible. We undertook a cross-sectional study in a population of definite carriers to estimate the proportion and to assess the clinical profile of carriers with symptoms. We also assessed a possible correlation between genotype and phenotype.
Methods: Carriers of DMD and BMD, aged 18-60 years, were traced through the files of the central register kept at the Department of Human Genetics in Leiden, Netherlands. For each carrier who agreed to participate a medical history was taken, and muscle-strength assessment by hand-held dynamometry and manual muscle testing and cardiological assessment were done.
Findings: 129 carriers of muscular dystrophy (85 DMD, 44 BMD) participated in the study. In 90 women from 52 (70%) families, 37 different mutations were found. 28 (22%) women had symptoms. 22 (17%) had muscle weakness, varying from mild to moderately severe. Muscle weakness was found in carriers of DMD and BMD, but dilated cardiomyopathy was found only in seven (8%) carriers of DMD, of whom one had concomitant muscle weakness. There was an unexpectedly high proportion of left-ventricle dilation (18%). No genotype-phenotype correlation was found.
Interpretation: Clinical manifestation of muscle weakness, dilated cardiomyopathy, or both can be found in about a fifth of carriers of DMD and BMD. If left-ventricle dilation is taken into account, the proportion of carriers with symptoms is even higher, amounting to 40%.