Segregation of chromosomes in spermatozoa of four Hungarian translocation carriers.

Objective: To determine the segregation pattern of the translocated chromosomes in spermatozoa of human males with translocations. Design: Retrospective case– control study. Setting: Hospital-based genetic laboratory for reproductive biology. Patient(s): A carrier with Y–autosome reciprocal translocation, two with autosome–autosome reciprocal translocations, and one with Robertsonian translocation. Intervention(s): Blood sample and sperm sample collection from each translocation carrier. Main Outcome Measure(s): Fluorescence in situ hybridization on lymphocyte slides to characterize each translocation case. Fluorescence in situ hybridization with specific DNA probes for each of the sperm samples to characterize the chromosomes involved in the rearrangement and to evaluate the possible interchromosomal effect for chromosomes 18, X, and Y. Result(s): Each translocation carrier showed a specific mode of segregation pattern of the translocated chromosomes, confirming the dependence on chromosomes involved in the translocation. The highest frequency from alternate segregation was with the carrier of Robertsonian translocation (90.9%), and the lowest was with the carrier of Y–autosome translocation (29.7%). No evidence of an interchromosomal effect for chromosomes 18, X, and Y were detected. Conclusion(s): Depending on the rate of the genetically normal and abnormal segregation modes, we can evaluate the chance of having a healthy proband. These results ensure more accurate genetic counseling for patients in assisted reproduction centers. (Fertil Steril 2007;88:212.e5–11. ©2007 by American Society for Reproductive Medicine.) Chromosomal abnormalities often lead to infertility. Structural chromosomal disorders are detectable from peripheral blood by karyotyping and metaphase fluorescence in situ hybridization (FISH) and account for 21% of all chromosome abnormalities (1). Robertsonian translocations and balanced reciprocal translocations are the most frequent structural chromosomal abnormalities, with an incidence of 1.23/1,000 (2) and 1/625 (3) newborns, respectively. The translocation carriers exhibit no particular phenotype, but they produce a large number of chromosomally unbalanced gametes. The widespread use of intracytoplasmic sperm injection technology may increase the possibility of transmitting the genetic defects to the offspring by avoiding severe steps of natural selection (4).