INCREASED RATE OF NONDISJUNCTION IN SEX CELLS DERIVED FROM LOW-QUALITY SEMEN

The relationship between chromosomal nondisjunction and semen quality was studied in two groups of males who differ highly in their semen qu ality: 12 individuals with low-quality semen caused by varicocele, and 8 subjects with high-quality semen, selected from sperm donors for in vitro fertilization. Chromosomal nondisjunction was inferred from the rate of disomy found in mature sperm cells. To determine the rate of disomy, we applied fluorescence in situ hybridization using satellite- specific probes for chromosomes 1, 15, 18, X and Y. In sperm cells of males with low-quality semen, the mean rate of disomy for each of the autosomes and of hetero-disomy for the sex chromosomes (XY) was signif icantly higher than that observed in the high-quality semen samples: m ore than 15-fold higher for chromosomes 1 and 15, and 7-fold higher fo r chromosomes 18 and XY Yet, the homo-disomy rate for each of the sex chromosomes (XX and YY) was almost the same in both types of semen. Th e large discrepancy between the low-and high-quality semen in the rate of sex chromosome hetero-disomy versus the similar rate of homo-disom y strongly suggests that the abnormal chromosomal segregation in meioc ytes of males with low-quality semen resulted from chromosomal nondisj unction at the first meiotic division. The results indicate that men s howing poor semen quality are at an increased risk for meiotic nondisj unction, similar to women at the end of their reproductive years.