Background: This study was aimed at evaluating the rate of pairing failure in pachytene spermatocytes of patients presenting either an obstructive (O) or a non-obstructive (NO) infertility.
Methods: Forty-one patients and 13 controls underwent testicular biopsy. Among the patients, 19 had an O infertility and 22 a NO infertility. Preparations of all patients and controls were Giemsa-stained, and synaptonemal complexes from nine of these patients and one control were immunostained.
Results: In all, 2931 pachytene nuclei were analysed. The mean rate of asynapsed nuclei from the NO group (25.4%) was significantly higher than that of the O group (9.8%). There was no significant difference between the O group and the controls (10.6%). Immunocytochemistry showed that the number of pachytene nuclei decreased from the early to late pachytene sub-stage in all patients. Two NO patients, one azoospermic and one oligozoospermic, had a high percentage of asynapsed nuclei (86 and 91.8% respectively); one of these patients also presented a precocious localized separation of sister chromatids.
Conclusion: high levels of extended asynapsis could arise from a primary meiotic defect which may be responsible for 9% of the NO male infertilities at our centre. The prevalence of early pachytene substages suggests that the pachytene checkpoint is localized at the mid-pachytene stage in humans.