BACKGROUND: Non-obstructive azoospermic (NOA) men can father children after testicular sperm extraction (TESE). Previous studies suggest that they may be at risk of producing chromosomally abnormal spermatozoa, but the number of sperm analysed per patient was usually very low. METHODS: Multicolour fluorescence in situ hybridization was used for detection of chromosome 13, 15, 16, 18, 21, 22, X and Y disomy and diploidy in sperm obtained from NOA men (n = 17) and control donors (n = 10). At least 500 testicular sperm were scored in each patient to increase the precision of our study. RESULTS: The mean frequency of overall disomy (2.32%) and diploidy (0.80%) found in 13 689 testicular spermatozoa of NOA patients was significantly higher than in the ejaculated sperm of normospermic control donors, disomy (0.62%) and diploidy (0.29%). A highly significant increase in frequencies of chromosome 15, Y and overall disomy (P < 0.001), and a significant increase in disomy of chromosome 13 (P = 0.002), 16 (P = 0.031) and 21 (P = 0.018), overall diploidy (P = 0.031) and diploidy caused by errors in meiosis I (P = 0.011) were observed in the NOA group. CONCLUSIONS: Testicular sperm samples of NOA patients show a higher incidence of numerical chromosomal abnormalities compared with ejaculated sperm of control donors. Appropriate genetic counselling is necessary in NOA men undergoing TESE.

Department of Genetics and Reproduction Veterinary Research Institute Hudcova 70 Brno 621 00 Czech Republic

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