Is mitochondrial DNA (MTDNA) quantification a potential biomarker for selection among euploid embryos?

Abstract

Recently, there have been controversial publications about the clinical relevance of mtDNA quantification in human blastocysts. Previous studies have not found an association between this parameter and ploidy, maternal age or pregnancy outcome. However, some laboratories, based on their evidence, apply this quantification as an implantation potential biomarker between euploid embryos. Different methodologies have been used for mtDNA assessment, mainly next generation sequencing (NGS) platforms and real-time polymerase chain reaction (qPCR), with consistent results between them. The aim of this study was to evaluate if there was a relationship between human blastocyst mtDNA content and female age, embryo ploidy and clinical pregnancy. Retrospective cohort study. A cohort of 447 blastocysts obtained from 202 couples, with an average female age of 33.8 years old (21-46), undergoing preimplantation genetic testing for aneuploidies (PGT-A) were included. Data was collected between April 2016 and March 2018 from a single center. Mosaic embryos (between 20%-80%) were excluded from this analysis. Trophectoderm biopsies were assessed by NGS (Veriseq-Illumina). For each sample, reads were aligned to the human reference genome (hg19) and the mtDNA genome separately. The number of reads that mapped to the mtDNA were divided by the number of reads that mapped to the nuclear DNA in order to normalize technical variability. The resulting values were mathematically adjusted by correction factors for embryo ploidy (complete chromosomal monosomies or trisomies) and gender previously reported. T-test was performed for statistical analysis in order to analyze mtDNA scores regarding embryo aneuploidy, maternal age and clinical pregnancy. Regarding all blastocysts analyzed, 236 (53%) were euploid and 210 (47%) aneuploid. The amount of mtDNA was significantly higher in aneuploid embryos (P= 0.0002). However, the amount of mtDNA was not different between euploid embryos from younger (<38 years, n=187) and older women (≥38 years, n=49) (P=0.6870). During the period covered, 65 single embryo transfer were performed after thawing, resulting in 37 (57%) HCG-beta subunit positive and 26 (40%) ongoing pregnancies. The mtDNA score from euploid blastocysts that achieved a clinical pregnancy was no significantly different from those that did not result in an ongoing pregnancy (P=0.7589). This study contributes evidence that mtDNA quantification in euploid embryos have no clinical impact in pregnancy outcome. mtDNA score was only statistically associated with chromosomal aneuploidy suggesting that high levels of mtDNA may have a negative impact resulting in an inadequate chromosome segregation.