Increased sperm mitochondrial DNA content in male infertility.

BACKGROUND There is increasing evidence that mitochondrial DNA (mtDNA) anomalies in sperm may lead to infertility. Point mutations, deletions and the presence of a specific mtDNA haplogroup have been associated with poor sperm quality, but little attention has been paid to the role of mtDNA content. METHODS Using density gradient separation and swim-up methods, we selected motile sperm from 32 normal and 35 abnormal sperm samples. The mtDNA/beta-globin gene ratio was determined by real-time quantitative PCR. RESULTS The average mtDNA/beta-globin ratio of sperm collected from 100% density layers was 1.4 for normal sperm, 6.1 for sperm samples presenting at least one abnormal criterion [among the three criteria established by World Health Organization (1999), i.e. sperm count, motility and morphology], and 9.1 for sperm samples presenting two or more of these abnormal criteria. These differences are very highly significant (P < 0.0001). The mtDNA numbers were also much greater in sperm collected from the 40% density gradient layers (mean: 17.1, P < 0.001), known to contain the most abnormal sperm of the sperm samples, than in those collected from the 100% layers known to contain sperm with the best fertilizing ability. CONCLUSION Our results showed significant mtDNA amplification in sperm collected from abnormal sperm samples.