[Acrocentric chromosomal associations in the families of children with Down's disease].

Acrocentric chromosome associations were studied in 373 persons: children with Down's syndrome, their parents and in controls. In parents with nondisjunction in the first meiotic division (M1) and in children with trisomy 21 due to parental nondisjunction in the M1 the increase of association activity of chromosome 21 was found out, compared with the parents-donors of the extrachromosome due to meiotic 2 (M2) errors, their children and control. The increased frequency of chromosome 21 associations in the whole group of parents (without taking into consideration the origin of odd chromosome) is also observed. It is particularly stressed that under studying the extrachromosome origin by cytological method the accumulation of marker variants of chromosome 21 occurs in groups of donors of the extrachromosome and their partners. This causes the absence of differences in association frequency between donors and donors' partners and prevents to study the integral picture of various factors contribution in the etiology of nondisjunction.