Aneuploid and unbalanced sperm in two translocation carriers: evaluation of the genetic risk

Translocation carriers have an increased risk of reproductive failure or affected offspring, because of the production of unbalanced gametes by meiotic segregation or the possible presence of interchromosomal effects (ICE). We therefore performed an analysis of meiotic segregation using the human-hamster IVF technique, and an aneuploidy assay for chromosomes 6, 18, 21, X and Y, using dual and triple-colour fluorescence in-situ hybridization, in two translocation carriers, t(1;13)(q41;q22) and t(3;19)(p21;p13.3). Sperm chromosome complements were analysed by whole chromosome painting. The frequencies observed for alternate, adjacent I, adjacent II and 3:1 segregations were, for t(1;13), 41.6, 41.6, 14.5 and 2.3% respectively, and for t(3;19), the frequencies were 39.1, 35.9, 21.8 and 3.2% respectively. More than 20,000 sperm per subject were analysed in the aneuploidy assay. Disomy 21 was found to be higher than other autosome disomies. Evidence for a possible ICE was found only in t(3;19). This study has shown that unbalanced sperm are more frequent than aneuploid sperm in the total sperm population. However, data in the literature suggest that the importance of each aberrant population seems to be more significant for embryo viability than would be expected from the increases in the percentages of abnormal sperm.