Bi-allelic variants in ASTL cause abnormal fertilization or oocyte maturation defects

Fertilization is a fundamental process of development, and the blocking mechanisms act at the zona pellucida (ZP) and plasma membrane of the egg to prevent any additional sperm from binding, permeating and fusing after fertilization. In clinical practice, some couples undergoing recurrent IVF failures that mature oocytes had abnormal fertilization for unknown reason. Ovastacin encoded by ASTL cleave the ZP protein ZP2 and play a key role in preventing polyspermy. Here, we identified bi-allelic variants in ASTL that are mainly characterized by fertilization problems in humans. All four independent affected individuals had bi-allelic frameshift variants or predicted damaging missense variants, which follow a Mendelian recessive inheritance pattern. The frameshift variants significantly decreased the quantity of ASTL protein in vitro. And all missense variants affected the enzymatic activity that cleaves ZP2 in mouse egg in vitro. Three knock-in female mice (corresponding to three missense variants in patients) all show subfertility due to low embryo developmental potential. This work presents strong evidence that pathogenic variants in ASTL cause female infertility and provides a new genetic marker for the diagnosis of fertilization problems.

Automated summary

Fertilization is a critical process in development, and the inhibition of additional sperm binding after fertilization is achieved through mechanisms acting at the zona pellucida and egg plasma membrane. This study identifies bi-allelic variants in the ASTL gene, which are associated with fertilization problems in humans. The identified variants in ASTL significantly decrease the protein levels or affect the enzymatic activity involved in preventing polyspermy. Knock-in mice carrying these variants show subfertility and reduced embryo developmental potential. These findings highlight the role of ASTL in female infertility and provide a new genetic marker for diagnosing fertilization problems.