OBJECTIVETo observe the characteristics of sperm single-stranded DNA breaks (SSB) and double-stranded DNA breaks (DSB) in infertile men, explore the association of DSB with male infertility, and provide a new observation index and idea for the diagnosis and treatment of the disease.

METHODSThis study involved 60 infertile men (infertility group) and 30 normal healthy males with infertile wives (control group). We comparatively analyzed the seminal parameters of the two groups, determined sperm concentration and viability using the computer aided sperm analysis system, measured the sperm survival rate by hypoosmotic swelling (HOS) test, examined sperm morphology by Diff-Quick staining, and detected sperm DNA damage by two-tail comet assay.

RESULTSNine two-tail comet models were established for detecting sperm DNA integrity. Comparisons between the fertility and control groups showed that the sperm DNA fragmentation index (DFI) was (33.8 ± 13.1) vs (16.3 ± 7.9)% (P < 0.01), the SSB-DFI was (19.2 ± 11.4) vs (14.9 ± 7.6)% (P > 0.05), the SSB-DFI/DFI was (56.8 ± 32.4) vs (91.4 ± 27.8)% (P < 0.01), the DSB-DFI was (23.9 +13.4) vs (6.1 ± 2.7)% (P < 0.01), and the DSB-DFI/DFI was (70.8 ± 19.5) vs (37.4 ± 11.3)% (P < 0.01). The optimal cut-off value of DSB-DFI/DFI in the diagnosis of male infertility was 39.5%, with the AUG, sensitivity, and specificity of 0.969, 98.3%, and 90%; that of DSB-DFI was 15.85%, with the AUC, sensitivity, and specificity of 0.912, 86.7%, and 80%; and that of DFI was 18.65%; with the AUC, sensitivity, and specificity of 0.861, 90%, 70%, respectively. In the infertile men, neither SSB-DFI nor SSB-DFI/DFI exhibited any correlation with semen parameters (P > 0.05); DFI was correlated negatively with the percentage of progressively motile sperm, sperm survival rate, and the percentage of morphologically normal sperm (P < 0.05 or P < 0.01), but not correlated with sperm concentration (P > 0.05); both DSB-DFI and DSB-DFI/DFI showed a negative correlation with sperm concentration, sperm survival rate, and the percentages of progressively motile sperm and morphologically normal sperm (P < 0.05 or P < 0.01).

CONCLUSIONDouble-stranded, rather than single-stranded DNA breaks, may be a factor inducing male infertility. The type of sperm DNA strand damage is of much reference value for the assessment of male fertility.