Successful live birth after preimplantation genetic testing for combined nuclear RNASEH2C and mitochondrial MT-TL1 variants.

INTRODUCTION

Preimplantation genetic testing (PGT) reduces reproductive risks for genetically high-risk families. To date, simultaneous PGT for nuclear and mitochondrial gene variants has rarely been reported. PGT targeting mitochondrial DNA (mtDNA) variants remains challenging and requires further clinical evidence.

CASE REPORT: We herein report a 3-year-old girl with severe global developmental delay. The proband harbored compound heterozygous RNASEH2C variants (maternal c.194G > A and paternal c.433C > T) and a maternally inherited m.3250 T > C variant in MT-TL1 with 72.9% heteroplasmy. PGT was performed for her parents, including RNASEH2C haplotype phasing, m.3250 T > C variant load quantification, and chromosomal copy number variation analysis. All eight embryos exhibited lower m.3250 T > C heteroplasmy (0-17.8%) than the mother (20.2%-27.9%). One aneuploid embryo with 17.8% heteroplasmy was aliquoted into 16 specimens for technical validation, and consistent variant loads (18.2% ± 1.7%) were observed across all aliquots. An euploid embryo carrying heterozygous RNASEH2C c.194G > A and low-level m.3250 T > C heteroplasmy (1.8%) was transferred, resulting in the birth of a healthy boy with uneventful birth and two-year postnatal follow-up.

CONCLUSIONS

This case represents a successful application of combined nuclear, mitochondrial, and chromosomal PGT in a family. Our findings provide valuable clinical evidence supporting blastocyst-stage PGT for mtDNA variants, indicating PGT to be a reliable reproductive option for females with low-level pathogenic mtDNA variants.