Multiple deletions of mitochondrial DNA are associated with the decline of motility and fertility of human spermatozoa

Sperm motility is one of the major determinants of male fertility and is required for successful fertilization. In a previous study, we demonstrated that the occurrence and accumulation of the 4977 bp deletion of mitochondrial DNA (mtDNA) is associated with diminished fertility and motility of human spermatozoa. The possible relationship between multiple deletions of mtDNA and the decline of fertility and motility in human spermatozoa was further explored in 36 subjects including subfertile and infertile males in this study. Using long-range polymerase chain reaction (PCR), we confirmed the 4977 bp deletion and identified two novel deletions of 7345 and 7599 bp of mtDNA in the spermatozoa with poor motility. We used Percoll gradients to fractionate spermatozoa with differing motility, and then screened for two novel large-scale deletions of the mtDNA. The results showed that the ratio of the deleted mtDNA in the spermatozoa with poor motility and diminished fertility were significantly higher than those in the spermatozoa with good motility and fertility. In addition, we found that the frequencies of the three large-scale deletions in the spermatozoa from patients with primary infertility and oligoasthenozoospermia were higher than those of the fertile males. Our findings suggest that mtDNA deletions may play an important role in some pathophysiological conditions of human spermatozoa.