Dosage effects of ZP2 and ZP3 heterozygous mutations cause human infertility

The zona pellucida (ZP) is an extracellular matrix universally surrounding mammalian eggs, which is essential for oogenesis, fertilization, and pre-implantation embryo development. Here, we identified two novel heritable mutations of ZP2 and ZP3, both occurring in an infertile female patient with ZP-abnormal eggs. Mouse models with the same mutations were generated by CRISPR/Cas9 gene editing system, and oocytes obtained from female mice with either single heterozygous mutation showed approximately half of the normal ZP thickness compared to wild-type oocytes. Importantly, oocytes with both heterozygous mutations showed a much thinner or even missing ZP that could not avoid polyspermy fertilization, following the patient's pedigree. Further analysis confirmed that precursor proteins produced from either mutated ZP2 or ZP3 could not anchor to oocyte membranes. From these, we conclude that ZP mutations have dosage effects which can cause female infertility in humans. Finally, this patient was treated by intracytoplasmic sperm injection (ICSI) with an improved culture system and successfully delivered a healthy baby.