Translocation (X;6) in a female with Duchenne muscular dystrophy: implications for the localisation of the DMD locus.

A female with Duchenne muscular dystrophy who was a carrier of a balanced translocation t(X;6)(p21;q21) is reported. Four other previously described (X;A) translocations associated with DMD share with the present case a breakpoint at Xp21. The extremely low probability of five independent (X;A) translocations having a breakpoint at Xp21 points to a non-rand association of this site with the DMD phenotype. A DMD locus at Xp21 could be damaged by the translocation, giving rise to Duchenne muscular dystrophy. Alternatively, a pre-existing DMD gene could weaken the chromosome, favouring breaks at Xp21.