Cytogenetic analysis of spermatozoa in the father of a child with a de- novo reciprocal translocation t(7;9) (q22;p23)

Analysis of sperm chromosomes was carried out in the father of a child with a de-novo reciprocal translocation t(7;9) (q22;p23) by G-banding and chromosome painting. Sperm metaphases were obtained using the zona-free hamster oocyte-human sperm fusion technique. A total of 138 complements were sequentially analysed by G-banding and fluorescence in-situ hybridization (FISH). The frequency of spermatozoa with structural chromosome abnormalities (5.1%) and the estimated conservative aneuploidy (1.4%) were within the range obtained in our control donors (6.9 and 4%). The sex ratio (45.3% X versus 54,7% Y) was not significantly different from the theoretical 1:1. A total of 309 sperm complements was analysed by FISH, 138 sequentially analysed by G- banding-FISH and another 171 analysed by FISH only. The frequencies of structural chromosome abnormalities for chromosomes 7 and 9 (0.6 and 0% respectively) were not significantly different from those obtained in our control donors (0.6 and 0.8%). No spermatozoa with the t(7;9) (q22;p23) were observed, showing no evidence for a germ-cell mosaicism. A statistically significant, positive association between sperm breakpoints and fragile sites (P = 0.0225) was observed. However, the coincidence between fragile sites and sperm breaks (80%) was not significantly different from that obtained in our control donors (79.2%). These results suggest that in this case the risk of structural chromosome abnormalities in further offspring is not increased, although an association between fragile sites and sperm chromosome breaks in the father does exist.