Analysis of polymorphism of CTG repetitive sequences in the gene of myotonic dystrophy in human populations of the Volga-Ural region

Distribution of CTG repetitive sequences in the myotonic dystrophy (MD) gen e was analyzed in ten populations of the Volga-Ural region, including Tatar s, Chuvashes, Maris, Udmurts, Mordovians, Komis, and four ethnogeographical groups of Bashkirs. A total of 25 alleles were found (9 to 14 in individua l populations), with each allele containing 5 to 34 trinucleotide repeats. The allele frequency distribution had two peaks corresponding to alleles wi th 5 and 11-14 CTG repeats. The frequency of the (CTG)(5) allele varied fro m 0.23 to 0.47 in Maris and Mordovians, respectively. Regarding the (CTG)(1 1-14) alleles, those containing 13 and 12 trinucleotides were most frequent in all populations; their frequencies varied from 0.15 in Mordovians to 0. 24 in Maris and Bashkirs from the Abzelilovskii raion (district). Alleles w ith large numbers of repeats (more than 30) were only found in Tatars and B ashkirs from the Abzelilovskii raion, where their frequency was 0.01. The d ata obtained were compared with those on other human populations from vario us regions of the world. In general, the populations of the Volga-Ural regi on took an intermediate position between European and Asian populations (al though were somewhat more similar to the latter ones) with respect to the d istribution of allelic frequencies of the CTG repetitive sequences. In indi vidual populations, the number of genotypes varied from 13 to 27 in Mordovi ans and Bashkirs from the Ilishevskii raion, respectively. The observed het erozygosity was the highest (91%) in Udmurts and the lowest (58%) in Mordov ians; the average heterozygosity was 81%. Such a high heterozygosity, as we ll as the revealed differentiation of the populations with respect to the d istribution of the allelic frequencies of CTG repetitive sequences in the M D gene, allow this polymorphic DNA locus to be considered a highly informat ive genetic marker of populations.