Clinical application of polar body-based preimplantation genetic testing for maternal mutations in women with a limited number of oocytes.

Abstract

Background: Trophectoderm (TE) cell biopsy at the blastocyst stage is currently the most common method used in preimplantation genetic testing for monogenic disorders (PGT-M). However, this approach may result in the wasting of some genetically unaffected embryos because only a proportion of zygotes develop to the blastocyst stage. Unaffected embryos, which degenerated during blastomere-blastocyst transformation, may give birth if transferred before the blastocyst stage and may be of great value to women with a low oocyte count. This study sought to investigate the potential application of polar-body (PB) biopsy in saving more genetically unaffected embryos for women with disease-causing mutations and a limited number of oocytes during PGT-M.

Methods: Three couples with female partners who had autosomal dominant or X-linked mutations in IRF6, FMR1, and EDA were recruited. The number of retrieved oocytes was limited to six per cycle. The first and second PBs (PB1 and PB2) of each oocyte were biopsied separately and subjected to multiple displacement amplification (MDA). The genotype of each embryo was determined by analyzing the MDA products of the corresponding PB1 and PB2 using a novel approach that combined direct mutation testing and single nucleotide polymorphism linkage analysis. Mutation-free embryos cryopreserved before the blastocyst stage were chosen for transfer.

Results: In total, four cycles were performed, resulting in the retrieval of 15 oocytes for three couples. The genotype of each embryo was successfully determined. Seven mutation-free embryos were discovered. Three of them were transferred, resulting in two clinical pregnancies, and the birth of two healthy infants. The accuracy of the embryo genotypes was validated by genetic testing of fetuses in the second trimester or at birth.

Conclusions: The PB-based strategy is feasible and effective for determining the mutation-carrier statuses of embryos in PGT-M for maternal mutations. Compared to blastocyst stage detection, this method may save a greater number of genetically unaffected embryos for patients. Further clinical trials are needed to determine whether PB biopsy is more beneficial than TE cell biopsy for women with disease-causing mutations and a limited number of oocytes in PGT-M.