[Heterozygous carrier rate for type I-IV proximal spinal muscular atrophy in Chuvashes, Udmurts, and residents of the Moscow region].

The first estimation of the heterozygous carrier rates for the SMN1 gene deletions and SMN2 gene duplications in populations of Russia has been performed. The numbers of SMNgene copies have been determined in samples from Chuvash and Udmurt populations, as well the population of the Moscow region, by means of multiplex ligation-dependent probe amplification. The heterozygous carrier rates for the CMA gene were 2.7% (1 : 37 people), 2.8% (1 : 36 people), and 2.8% (1 : 36 people) in Chuvashes, Udmurts, and residents of the Moscow region, respectively. The SMN2 duplication frequencies have been determined in the studied groups. It is 1.5, 4, and 2.5% in Chuvashes, Udmurts, and residents of the Moscow region, respectively. The high SMN2 duplication frequency in Udmurts may explain why the SMN1 heterozygous carriage frequency in this population was overestimated in earlier PCR-RFLP analyses.