P-706 Non-invasive analysis of mitochondrial DNA mutation for embryo evaluation.
Authors: Ijuin A , Hayama T , Ueno H , Hamada H , Miyakoshi A , Sueyoshi S , Saito M , Tochihara S , Takeshima T , Sakakibara H , Miyagi E , Murase M 
Published: June 2023

Abstract

Study question
Is it possible to amplify whole mitochondrial DNA (mtDNA) and detect all mtDNA mutation in human embryo from spent media after embryo culture?

Summary answer
We were able to amplify whole mtDNA from 43% of spent medium after 24-hour culture. The most of mtDNA mutation in embryo could be detected.

What is known already
Preimplantation genetic testing for aneuploidy (PGT-A) with embryo biopsy is now commonly used to improve pregnancy rate. However, invasive embryo biopsy requires highly trained embryologist and induced higher risk of pre-eclampsia. Therefore, non-invasive methods with cell-free DNA in spent medium have been studied. Our group previously showed euploid or viable embryos at post-implantation stage have lower number of non-synonymous mtDNA mutations and this may help to select the best blastocyst to transfer. Although cell-free DNA is reported to contain mtDNA, it remains unclear whether mtDNA mutations number can be assessed from cell-free DNA.

Study design, size, duration
Donated low grade blastocysts were cultured for additional 24 hours with new media, cell-free mtDNA were obtained from the spent culture medium (non-invasive samples). For comparison, trophectoderm cells were biopsied from each embryo (invasive sample). The mtDNA selective amplifications were done to both samples. We performed mtDNA sequencing by next generation sequencing (NGS) and compared mtDNA mutations between non-invasive and invasive samples to clarify the capability of non-invasive assessment for mtDNA mutation.

Participants/materials, setting, methods
Under the ethical review of Yokohama City University and informed consent with patients, we collected human blastocysts which were discarded because of slow development or morphologically low-grade. We extracted whole DNA from biopsy and medium samples and selectively amplified mtDNA by long-range PCR for two overlapping amplicons. The mtDNA sequencing with NGS was performed to successfully amplified mtDNA. The 90% or more heteroplasmy level non-synonymous mutations were investigated.

Main results and the role of chance
We collected 34 discarded embryos from 13 patients. All embryos were cultured individually for additional 24 hours with 20 μl drop of newly prepared media. Amplified mtDNA were visualized by the presence of 8 kb band following agarose gel-apheresis for two fragments PCR. Both fragments were detected in 41% (14/34) of non-invasive samples and all invasive samples. Only one fragment was detected in 14% (5/34) of non-invasive samples. The completely amplified non-invasive samples and corresponding invasive samples were performed mtDNA sequencing with NGS. In results, 13 non-synonymous mutations were identified in invasive samples. All of these mutations were also detected in non-invasive samples. Although the number and location of mutations completely matched between the invasive and non-invasive samples in 78.5% (11/14) embryos, in other 3 embryos, mtDNA mutation numbers were higher in non-invasive samples even though no mutation existed in invasive samples. This means, if selective mtDNA amplification is completed, mtDNA mutations can be evaluated from the non-invasive samples with a probability of about 80% but include 20% false positive mtDNA mutations. To realize this, we need to improve the mtDNA amplification method.

Limitations, reasons for caution
We can used only clinically discarded embryos because ethical restriction. And it was necessary to additional 24-hours culture to obtain individually cultured spent media because embryos are co-cultured until they are donated. Because of small number of samples available, we keep collecting more samples for more accurate evaluation.

Wider implications of the findings
If the mtDNA mutations can be analyzed from spent medium, high-quality embryos can be selected without invasive embryo biopsy and complicated procedure. If this non-invasive mtDNA analysis can be performed to clinical embryo for embryo transfer, it may contribute to further improvement of pregnancy rate without any invasion to embryo.

Trial registration number
the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant-in-Aid for Scientific Research C (Grant Number JP21K09474) and Early-Career Scientists (Grant Number JP20K18169)