Mutation in <scp> <i>MSH5</i> </scp> Causes Primary Ovarian Insufficiency and Successful Therapeutic Intervention by In Vitro Fertilisation

Primary ovarian insufficiency (POI) is a genetically heterogeneous disorder characterised by cessation of menstruation before the age of 40 years with elevated levels of follicle-stimulating hormone. Germline variants in the MSH5 gene cause POI. In this study, we investigated a Han Chinese family with POI. The proband and her two younger sisters are clinically diagnosed with POI. The proband's parents are phenotypically normal. Whole exome sequencing identified a novel homozygous splice-donor site (c.271+1G>A) variant in the first nucleotide of intron 3 of the MSH5 gene in this proband. Sanger sequencing confirmed that both the younger sisters of the proband also harbour the same homozygous variant, while the proband's parents are carrying this variant in a heterozygous state. This variant causes aberrant splicing of MSH5 mRNA followed by the formation of an alternative MSH5 transcript with complete loss of exon 3. Relative expression of mutant MSH5 mRNA is significantly reduced compared to that of the wild-type transcript. Mutant MSH5 impaired DNA homologous recombination repair as well as significantly lowering the clonogenic survival rate of cell clone formation compared with the wild type. In addition, we also found a significantly higher apoptotic rate and lower cell proliferation rate in the mutant than that of the wild type. We performed egg donation-based in vitro fertilisation for this proband, and two healthy baby girls have been successfully delivered. Our present study reports the first splice-site variant in the MSH5 gene in patients with POI. We also report for the first time the successful therapeutic intervention by in vitro fertilisation for patients with MSH5-associated POI.