A STUDY ON DUPLICATIONS OF THE DYSTROPHIN GENE - EVIDENCE OF A GEOGRAPHICAL DIFFERENCE IN THE DISTRIBUTION OF BREAKPOINTS BY INTRON

Starting from a group of 265 Italian patients affected with Duchenne o r Becker muscular dystrophy a screening for duplications in the dystro phin gene was performed on 112 cases in which no deletions had previou sly been detected. The 21 intragenic duplications detected account for 7.9% of the total. Among these, one duplication including exons from 3 to 43 is the largest reported so far. Data from this study were comb ined with those from the literature and breakpoint distribution by int ron was analysed. In general breakpoints occur mostly in the proximal third of the gene, in particular in intron 7. However, both the freque ncy of duplications and the distribution of breakpoints by intron are different in the Japanese sample compared with the other groups of pat ients. The role of geographical differentiation of intron sequences by genetic drift and of transposon-like sequences in explaining these di fferences is discussed.