Mitochondrial DNA copy number in peripheral blood: a potential non invasive biomarker for female subfertility

Study question: Does the mitochondrial DNA copy number (mtDNAcn) in peripheral blood have the potential to serve as a non invasive biomarker for female subfertility? Summary answer: A mtDNA peripheral blood level below 105 mtDNAcn resulted associated with a five-folds increased risk of subfertility, providing a possible way of predicting this condition. What is known already: Low mtDNA content in oocytes and in cumulus cells is a significant indicator of poor oocyte quality and may prevent the oocyte from completing the process of fertilization and embryo development. Furthermore, and of utmost relevance, is the recent evidence showing a correlation between mtDNA content in cumulus cells and mtDNAcn in peripheral blood cells. Study design, size, duration: This is a nested case-control study drawn from a prospective cohort of pregnant women referred for routine first trimester screening for aneuploidies (from 11+0 to 12+6 weeks of gestation) between January 2012 and March 2013 at the “Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico” of Milan, Italy. Participants/materials, setting, methods: Cases were subfertile women who attempted to become pregnant for 12–24 months. Controls were the two subsequently age-matched women who became pregnant in less than one year. Blood samples were obtained from all participating women. MtDNA was quantified using real time PCR and normalized to nuclear DNA. Main results and the role of chance: One hundred and four subfertile women and 208 matched fertile controls were selected. The median (interquartile range) mtDNAcn was 95 (73-124) and 145 (106-198), respectively (p<0.001). The area under the receiver operating characteristic (ROC) curve was 0.73 (95% Confidence Interval-CI: 0.67-0.79) (p<0.001). The Youden index was 105 mtDNAcn. The crude odds ratio for subfertility in women with mtDNAcn below this threshold was 5.72 (95%CI: 3.43-9.55). We repeated these analyses in different age groups: the accuracy of mtDNAcn assessment in peripheral blood resulted higher in younger women and progressively decreased with increasing age. Limitations, reasons for caution: We did not perform an infertility diagnostic work-up of the couples and we are thus unable to rule out other potential causes of subfertility. However, severe concomitant causes of infertility can be confidently ruled out since all women conceived within two years. Wider implications of the findings: MtDNAcn assessment in peripheral blood appears to have all the features of the much sought non-invasive biomarker of female fertility. Noteworthy its performance resulted very good in young women. Our results may thus have future clinical applications. However, further independent studies including non-pregnant women undergoing high throughput screening are warranted. Trial registration number: Not applicable.