Human mitochondrial DNA haplogroup M8a influences the penetrance of m.8684C>T in Han Chinese men with non-obstructive azoospermia

Research question: What is the role of mitochondrial DNA (mtDNA) in the pathogenesis of non-obstructive azoospermia (NOA)? Design: mtDNA genome sequencing followed by an independent population validation were performed in 628 NOA cases and 584 healthy controls. Antioxidant capacity of serum was evaluated in 54 randomly selected cases out of 536 and 49 out of 489 controls. Results: In the screening stage, 13 mtDNA haplogroups (hg) were ascertained, and 10 susceptible variants were observed. In the validation stage, hg M8* in individuals was found to be associated with increased risk of NOA [odds ratio (OR) 2.61, 95% confidence interval (CI) 1.47–4.61] (P=0.001). Unexpectedly, the frequency of m.8684C>T, the defining marker for hg M8a, was also higher in NOA (OR 4.14, 95% CI 1.56–11.03) (P=0.002). Subsequently, the frequency distributions were compared among the sub-hg of hg M8* (including hg M8a, C and Z) and, intriguingly, no significance was found in hg C and Z. Additionally, the level of total antioxidant capacity was significantly decreased (PT in NOA, and mtDNA genetic variants (causing low antioxidant levels) might increase mtDNA damage and impair normal spermatogenesis.