Sperm mitochondrial DNA copy numbers in normal and abnormal semen analysis: A systematic review and meta-analysis

Background: Normal mature sperm have a considerably reduced number of mitochondria, which provide the energy required for progressive sperm motility. Literature suggests that disorders of sperm motility may be linked to abnormal sperm mitochondrial number and function.

Objectives: To summarise the evidence from literature regarding the association of mitochondrial DNA copy numbers and semen quality with a particular emphasis on the sperm motility.

Search strategy: Standard methodology recommended by Cochrane.

Selection criteria: All published primary research reporting on the association between mitochondrial DNA copy numbers and semen quality.

Data collection and analysis: Using standard methodology recommended by Cochrane we pooled results using a random effects model and the findings were reported as a standardised mean difference.

Main results: We included ten studies. The primary outcome was sperm mitochondrial DNA copy numbers. A meta-analysis including five studies showed significantly higher mitochondrial DNA copy numbers in abnormal semen analysis compared with normal semen analysis (standardised mean difference 1.08, 95% CI 0.74-1.43). Seven studies included in the meta-analysis showed a significant negative correlation between mitochondrial DNA copy numbers and semen parameters. The quality of evidence was assessed as good to very good in 60% of studies.

Conclusions: Our review demonstrates significantly higher mitochondrial DNA in human sperm cells of men with abnormal semen analysis in comparison to men with normal semen analysis.

Tweetable abstract: There is significantly higher mitochondrial DNA in sperm cells of men with abnormal semen analysis in comparison to men with normal semen analysis.