A novel homozygous variant in ZP2 causes abnormal zona pellucida formation and female infertility.

Purpose: We aimed to identify pathogenic variants in two infertile sisters in a family with a thin zona pellucida (ZP) phenotype.
Methods: Whole-exome sequencing was performed in the two affected sisters, and Sanger sequencing was used to confirm the identified variants. The effects of the identified variant were further investigated in mouse oocytes and Chinese hamster ovary (CHO) cells.
Results: We identified a novel homozygous frameshift variant in ZP2 (c.1235_1236del, p.Q412Rfs*17) in the two affected individuals. Immunoblotting demonstrated that the variant produced a truncated ZP2 protein that was expressed at low levels in CHO cells. Immunofluorescence in mouse oocytes confirmed the decreased protein level of mutant ZP2, although the subcellular localization was not affected. In addition, immunoprecipitation showed that the pathogenic variant reduced the interaction between ZP2 and ZP3.
Conclusion: This study identified a novel pathogenic variant in ZP2 that produces a truncated ZP2 protein. The variant might disrupt the assembly of ZP2-ZP3 dimers, thus resulting in a thin ZP and female infertility.