Mapping of Xp21 translocation breakpoints in and around the DMD gene by pulsed field gel electrophoresis

Balanced translocations with a breakpoint in the Xp21 region are likely to disrupt the giant Duchenne muscular dystrophy (DMD) locus and can be demonstrated in females suffering from the disease. Pulsed field gel electrophoresis allows the positioning of these breakpoints by detecting junction fragments on the derived chromosomes; DNA probes hybridizing to these fragments may be located as many as several hundred kilobases away from the breakpoints. By using this approach, 11 translocation breakpoints from the Xp21 region have been analyzed. The localization of three previously examined breakpoints was confirmed. Six other breakpoints, including a breakpoint flanking the DMD gene and not associated with the DMD phenotype, could be positioned relative to SfiI sites on a 3.5-Mb restriction map of the region.