Abstract

We have investigated an extended pedigree with three cousins affected by Duchenne muscular dystrophy with apparent transmission through the male line. However, molecular studies have shown that one boy has a de novo duplication, another has a deletion, and the molecular mutation has yet to be defined in the third boy. All three X chromosomes in the affected boys appear to have a different origin. We speculate on the mechanisms by which the Duchenne locus may be particularly prone to mutation in this family and the possible involvement of transposons is discussed. Whatever the mechanism involved, the occurrence of three different mutations in one pedigree is a rare event.