[Mutational level of translocated variants of Down's syndrome in Leningrad (1982-1991)].

Karyological study of 644 newborns with Down's syndrome (DS) revealed 37 translocation cases (5.7%). Translocations were inherited in 8 cases, in 17 cases they were sporadic, and in 12 cases parents were not examined. Total mutation rate per gamete per generation (2.7.10) and mutation rates of D/21 and G/21 translocations in different female age groups were calculated. The obtained data are in good agreement with results of research in other world regions. Literature data on the parental origin of de novo translocations for DS are presented. The role of meiotic coorientation of nonhomologous chromosomes in anomalies of spermatogenesis is discussed.