As the resolution and accuracy of diagnostic techniques for preimplantation genetic testing for aneuploidy (PGT-A) are improving, more mosaic embryos are being identified. Several studies have provided evidence that mosaic embryos have reproductive potential for implantation and healthy live birth. Notably, mosaic embryos with less than 50% aneuploidy have yielded a live birth rate similar to euploid embryos. This concept has led to a major shift in current PGT-A practice, but further evidence and theoretically relevant data are required. Proper guidelines for selecting mosaic embryos suitable for transfer will reduce the number of discarded embryos and increase the chances of successful embryo transfer. We present an updated review of clinical outcomes and practice recommendations for the transfer of mosaic embryos using PGT-A.

Min Jee Kim, Sun Ok Park, Ye Seul Hong, Eun A Park, Yu Bin Lee, Byung-Ok Choi, Kyung-Ah Lee, Eun Jeong Yu, and Inn Soo Kang. J Genet Med 2022;19:7-13. https://doi.org/10.5734/JGM.2022.19.1.7

Background: Charcot–Marie–Tooth disease (CMT) is a genetically and clinically heterogeneous group of progressive peripheral neuropathies. Preimplantation genetic testing for monogenic disorders (PGT-M), a well-established assisted reproductive technology used to detect specific genetic mutations in embryos before implantation, has been used in common CMT subtypes (e.g., CMT1A); however, data on its application across rarer subtypes and in de novo cases remain limited. In this study, we aimed to evaluate the effectiveness of PGT-M using karyomapping in achieving clinical pregnancies and healthy births in families affected by various CMT types, including the previously unreported subtypes CMT1B and CMT2. Methods: We analyzed 31 PGT-M cycles from 13 families with genetically confirmed CMT, including cases of previously unreported subtypes CMT1B and CMT2. A total of 150 embryos were biopsied. Through 19 embryo transfer cycles, 21 embryos were transferred. In one de novo case, karyomapping was performed using amniotic fluid from an affected fetus as a reference. Results: Of the 19 embryo transfers, 15 resulted in clinical pregnancies. Prenatal diagnosis confirmed that all fetuses were unaffected, and all pregnancies resulted in healthy live births. Successful phasing using amniotic fluid from an affected fetus enabled accurate embryo selection and led to the birth of healthy twins. Conclusions: PGT-M using karyomapping is a rapid and reliable method for achieving successful pregnancies in families affected by diverse CMT subtypes, including de novo cases, and supports broader applicability to other monogenic disorders.

Background/Objectives: Mosaicism in preimplantation embryos has important implications for embryo selection and reproductive outcomes. This study investigates the age-related frequency of mosaicism, analyzes its subtypes, and evaluates its clinical significance. Methods: A total of 36,506 blastocysts were analyzed using next-generation sequencing-based preimplantation genetic testing for aneuploidy between January 2021 and December 2023. The overall frequencies of euploid, aneuploid, mosaic, and no-call embryos were 20%, 56%, 23%, and 1%, respectively. In this study, we propose a new classification. Embryos were classified into two categories: Mosaic-A, referring to embryos identified as mosaic in standard genetic testing reports, and Mosaic-B, which includes both Mosaic-A and aneuploid embryos containing mosaicism. Results: The proportion of Mosaic-A embryos significantly decreased with maternal age (31% in women 42 years). By contrast, Mosaic-B embryos, which include Mosaic-A and aneuploid embryos with mosaicism, increased with age (46%, 49%, 53%, 56%, and 62% across the same age groups). Notably, as maternal age advanced, low-level complex mosaicism decreased, whereas high-level complex mosaicism significantly increased (p < 0.001, chi-square test for trend). Other mosaicism subtypes followed similar trends. These findings suggest that the increase in high-level complex mosaicism resulted from a higher incidence of post-zygotic mitotic errors occurring earlier in development and affecting a larger proportion of cells in older women. Conclusions: This study underscores the significance of incorporating a broader classification of mosaicism, including Mosaic-A and B, to enhance understanding of the biological behavior of mosaic embryos according to age and highlights the clinical importance of cryopreserving high-level or complex mosaic embryos for transfer in women of advanced age.

Background/Objectives: Karyomapping, a genome-wide SNP analysis, has drastically changed the approach to preimplantation genetic testing for monogenic disorders (PGT-M). However, there are cases in which karyomapping cannot be applied due to an insufficient number of informative SNPs. In this study, we aimed to analyze for the first time whether an insufficient number of informative SNPs is related to the family member used as a reference. Methods: For the karyomapping pre-clinical test, in addition to the couple, one of the DNA samples from an additional family member (children, parent, sibling) is used as a reference for phasing the SNP allele. We analyzed 263 couples who underwent karyomapping for PGT-M at the CHA Fertility Center from May 2020 to December 2022. karyomapping data was scanned on an Illumina NextSeq and analyzed through the BlueFuse Multi software version 4.5. Results: Preclinical karyomapping tests were performed in 263 couples with 58 monogenic diseases. Karyomapping was applicable to PGT-M for 241 (91.6%) couples and not applicable for 22 (8.4%) couples. The percentages of “not applicable” cases according to the reference family member were 1.3% (1/80) in the children group, 5.4% (8/148) in the parent group, and 37.1% (13/35) in the sibling group. Among the genetic diseases studied, couples with neurofibromatosis type 1 (6/27, 22.2%) and Kennedy disease (5/5, 100%) had the highest rate of non-applicable cases. Conclusions: Our results suggest that a child or parent may be better than the sibling for karyomapping in PGT-M. These data provide useful information for selecting a reference among the family members for preclinical karyomapping tests.