DNA Methylation Abnormalities at Imprinted Loci in Oligospermic and Azoospermic Men

OBJECTIVE: To assess DNA methylation at imprinted and repetitive genomic regions in ejaculated and testicular sperm from men with oligospermia, azoospermia, and those undergoing vasectomy reversal, compared with fertile controls. DESIGN: Observational case-control study. SUBJECTS: Samples were obtained from 68 men, including 29 infertile men (18 oligospermic [5-15 million/mL], 11 severely oligospermic [<5 million/mL]) and 20 fertile controls with confirmed natural conceptions. Testicular tissue was collected from 11 azoospermic men (7 obstructive azoospermia [OA], 4 non-obstructive azoospermia [NOA]) and 8 men with prior paternity undergoing vasectomy reversal (VR). EXPOSURE: Sperm DNA methylation at four imprinted genes (H19, GTL2, MEST, LIT1) and one repetitive element (LINE1). MAIN OUTCOME MEASURES: Methylation levels at CpG sites determined by bisulfite pyrosequencing. RESULTS: H19 was significantly hypomethylated only in severe oligospermia compared to fertile controls, while other groups showed non-significant trends with overlapping distributions. In contrast, MEST was significantly hypermethylated in oligospermic, azoospermic, and VR groups compared with fertile controls. No significant differences were observed for GTL2, LIT1, or LINE1. CONCLUSION: DNA methylation abnormalities in sperm are locus-specific and vary across infertility phenotypes. MEST alterations were consistent across groups, whereas H19 changes were limited to severe oligospermia. Similar methylation patterns in testicular sperm from azoospermic and vasectomy reversal groups suggest that epigenetic alterations may reflect the testicular environment or obstruction, or differences between testicular and ejaculated sperm.