Résumé :
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Communication n° 153 Introduction : Duchenne muscular dystrophin (DMD) gene is the longer gene composed of 79 exons spanning 2.3 Mb on X chromosome. Recombination rates along the gene have been mostly documented for its 5' and central part (until exon 59) where informative polymorphic markers are well described and available. However, the lack of available informative markers in the distal part of the DMD gene failed to solve genetic counselling in some families and do not allow studies of the evolutionary pattern of the gene. Methods and results : In view to identify novel markers in the 3'end of the gene, we have performed a systematic search of dinucleotidic sequences in public databases with restrictive criteria (more than 10 repeat; GC content < 40%). Four repeat sequences fulfill these conditions: one in intron 67 (IVS67) one in intron76 (IVS76) and two (3'UTR-1 and 3'UTR-2) in the 3'-UTR region of the gene (250kb downstream from the stop codon). Fluorescent labelled oligonucleotides were designed to amplify these dinucleotide repetitive sequences and DNA of 78 subjects given a total of 108 chromosomes were studied with standard procedures (on an automated sequencer). Conclusion : The results of this analysis conclude that three of these repeats (IVS 67, IVS 76 and 3'UTR-1) are of interest, with consistent allele frequencies, Heterozygosity and Polymorphism Information Content (PIC). These new markers were successfully applied in two families where the causative mutation could not be identified and where the carrier status of some relative females could not be established. Moreover, we will estimate the genetic distances as well as the recombination rates/ linkage disequilibrium along the DMD gene.
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