A region in the dystrophin gene major hot spot harbors a cluster of deletion breakpoints and generates double-strand breaks in yeast

Deletions within the dystrophin gene (DMD) account for >70% of mutations leading to Duchenne and Becker muscular dystrophies (DMD and BMD). Deletion breakpoints were reported to be scattered within regions that also represent meiotic recombination hot spots. Recent studies indicates that deletion junctions arise from nonhomologous end joining (NHEJ), a major pathway for repairing DNA double-strand breaks (DSBs) in mammals. Here we show that a region in intron 47 (i.e., a major deletion hot spot in the DMD gene) generates DSBs during meiosis in yeast and harbors a cluster of previously sequenced deletion breaks. Mapping of breakpoints in 26 BMD/DMD patients indicated that the frequency of breakpoint occurrence around this region is 3-fold higher than expected by chance. These findings suggest that DSBs mediate deletion formation in intron 47 and possibly account for the high frequency of meiotic recombination in the region. Statistical analysis indicated the presence of at least one other breakpoint cluster in intron 47. Taken together, these results suggest that the primary events in deletion formation occur within discrete regions and that the scattered breakpoint distribution reflects both a variable degree of DSB end processing and the availability of a small (compared to the huge regions involved) deletion junction sample.