Sequential FISH allows the determination of the segregation outcome and the presence of numerical anomalies in spermatozoa from a t(1;8;2)(q42;p21;p15) carrier.

PURPOSE: To find out the meiotic segregation behaviour of the t(1;8;2)(q42;p21;p15), to evaluate the occurrence of interchromosomal effects, and to determine whether there is an accumulation of unbalanced products in aneuploid/diploid gametes. METHODS: A sequential FISH protocol based on two successive hybridization rounds over the same spermatozoa was performed to determine the segregation outcome of the rearranged chromosomes. The presence of numerical abnormalities for 13, 18, 21, X and Y was also evaluated by sperm FISH. Those aneuploid/diploid gametes were subsequently relocalized and analyzed for their segregation content through additional hybridization rounds. RESULTS: The segregation pattern observed reported a very low production of normal/balanced gametes (11.7 %). Significant increased frequencies of diploidies and disomies for chromosomes X/Y and 18 were detected (p < 0.001). Aneuploid and diploid spermatozoa displayed significant increases of 5:1, 6:0 and other unexpected disjunction modes (p < 0.001). CONCLUSIONS: The strategy developed in this study is a reliable new approach to establish the full segregation pattern of complex chromosome rearrangements (CCR). Results corroborate the low number of normal/balanced spermatozoa produced by CCR carriers and support previous findings regarding an altered segregation pattern in gametes with numerical abnormalities. Altogether this confirms the importance of PGD as a tool to prevent the transmission of chromosomal abnormalities to the offspring in CCR patients.