Novel mutations in ZP1, ZP2, and ZP3 cause female infertility due to abnormal zona pellucida formation

The human zona pellucida (ZP) is an extracellular glycoprotein matrix composed of ZP1, ZP2, ZP3, and ZP4 surrounding the oocyte, and it plays an important role in sperm-egg interactions during fertilization. Structural and functional changes in the ZP can influence the process of fertilization and lead to female infertility. Previous studies have identified mutations in ZP1, ZP2, and ZP3 that lead to female infertility caused by oocyte degeneration, empty follicle syndrome, or in vitro fertilization failure. Here we describe seven patients from six independent families who had several abnormal oocytes or suffered from empty follicle syndrome, similar to the previously reported phenotypes. By whole-exome sequencing and Sanger sequencing, we identified several novel mutations in these patients. These included three homozygous mutations in ZP1 (c.1708G > A, p.Val570Met; c.1228C > T, p.Arg410Trp; c.507del, p.His170Ilefs*52), two mutations in a compound heterozygous state in ZP1 (c.1430 + 1G > T, p.Cys478X and c.1775-8T > C, p.Asp592Glyfs*29), a homozygous mutation in ZP2 (c.1115G > C, p.Cys372Ser), and a heterozygous mutation in ZP3 (c.763C > G, p.Arg255Gly). In addition, studies in CHO cells showed that the mutations in ZP1, ZP2, and ZP3 might affect the corresponding protein expression, secretion, and interaction, thus providing a mechanistic explanation for the phenotypes. Our study expands the spectrum of ZP gene mutations and phenotypes, and provides a further understanding of the pathogenic mechanism of ZP gene mutations in vitro.