Muscular dystrophy ingirls withX;autosome translocations

SUMMARY Twentyknowncases ofX;autosome translocations withbreakpoints atXp2l associated withDuchenne or Beckermuscular dystrophy ingirls are reviewed. Thevariable severity described fordifferent personsmay reflect differences inX inactivation orinthenature ofthegenomic targetdisrupted. Highresolution cytogenetic studies on 12casesindicate breakpoints on theX chromosome atXp211or Xp21l2. Translocation chromosomes from several ofthese caseshavebeenisolated inhuman/mouse somatic cell hybrids. Molecular heterogeneity inthebreakpoint positions hasbeenestablished byprobing DNA fromthese hybrids with a rangeofcloned sequencesknowntobelocated within, orclosely linked to,the Duchenne region. Theminimumseparation between themostdistal andthemostproximal breakpoints is176kbsuggesting that, ifasingle gene isinvolved, itmustbelarge. Alternatively, thetranslocations may affect different genes,orconfer alterations toregulatory sequenceswhich operateata distance.