[Precise preimplantation genetic testing for a Chinese pedigree carrying a small segmental copy number variation]

To block family transmission of a small fragment copy number variation (CNV) with combined 1 Mb resolution preimplantation genetic testing for aneuploidy (PGT-A) and target region preimplantation genetic testing for monogenic disease (PGT-M) strategies.

A couple who attended the Reproductive and Genetic Medicine Center of Dalian Women and Children's Medical Center (Group) in 2024 were selected as the study subject. Upon the woman's two pregnancies, ultrasound examination revealed fetal abnormalities, and CNV-seq based on low-depth whole genome sequencing revealed that both fetuses had carried a maternal 17p12 microduplication of approximately 1.43 Mb. Microduplication in this region has been associated with Charcot-Marie-Tooth disease type 1A. In view of the fact that the resolution of conventional PGT-A detection cannot meet the requirement of small fragment CNV analysis, and conventional PGT-M assay cannot directly determine the CNV, two detection schemes were adopted. On the one hand, PGT-A testing with 1 Mb resolution was performed on the embryo to directly determine whether it carries the above microduplication. At the same time, the couple and their fetus were subjected to chromosomal typing scheme for the 17p12 region to indirectly identify embryos carrying the risk chromosome for microduplication. This study has been approved by the Medical Ethics Committee of the Hospital (Ethics No: FEJT-KY-2025-51).

Three embryos were tested after the first PGT cycle, of which 1 was not carrying the pathogenic variant and was euploid, whilst the other 2 embryos were carrying the 17p12 microduplication, and 1 of them was aneuploid. After genetic counseling, the euploid embryo without the 17p12 microduplication was selected for transfer, and prenatal diagnosis based on amniotic fluid sample showed that the fetal chromosomal karyotype was normal and did not carry the 17p12 microduplication.

The combined application of high-resolution PGT-A and PGT-M typing detection of the target region can effectively block family transmission of the CNVs of small fragments.