GENETIC SEGREGATION OF MITOCHONDRIAL 3697>GA MUTATION IN PGD CYCLES

To explore the dynamics and inheritance of m.3697G>A mutation and the performance of preimplantation genetic diagnosis (PGD) for mutant carriers. To analyze whether the cumulus cells surrounding oocytes can be used as a noninvasive PGD indicator for maternal inherited mtDNA mutation. The study encompassed a pedigree of four m.3697G>A carriers, including one asymptomatic PGD patient and one LS patient. Next generation sequencing (NGS) was used to detect m.3697G>A heteroplasmy in blood samples from the pedigree. Twelve cumulus oocyte complexes (COCs) were collected in the first PGD cycle and 11 COCs in the second cycle from the patient. Cumulus cells were isolated from COCs. Trophectoderm (TE) cells were biopsied from blastocysts on day 5 or day 6. The mutation load of TE biopsies, arrested embryos, blastomeres, polar bodies, the degenerate oocyte and corresponding cumulus cells were analysed via NGS. From 23 COCs, 20 oocytes were fertilized successfully via intracytoplasmic sperm injection. On day 5 or day 6 post-fertilization, 15 blastocysts were obtained and biopsied. The mutation load of the 15 TE biopsies (ranged from 15.2% to 100%), allowing selection of embryos for implantation. In the first cycle, a blastocyst with mosaic chromosomal copy number and mutation load of 31.7% was opted for transfer. However, the patient failed to yield a clinical pregnancy. In the second PGD cycle, a euploid blastocyst with mutation load of 53.9% was selected to transfer, which enable her to carry a successful pregnancy. Now she is in the stage of second trimester. Mutation load of cumulus cells may not correlate well with TE mutation load. This study first reported that m.3697G>A mutation showed a random pattern of inheritance in PGD embryos, it is almost impossible to produce zero or very low heterogenous embryos. But PGD could be applied to reduce risk of inheritance of a high mutation load and to yield successful pregnancy. Cumulus cells are not a suitable predictor of late-stage embryo mutation load.