MOS is a novel genetic marker for human early embryonic arrest and fragmentation.

Early embryonic arrest and fragmentation (EEAF) is a common phenotype observed in in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) cycles. The phenotype causes female infertility and recurrent failed IVF/ICSI attempts. However, the molecular mechanisms behind EEAF remain largely unknown. In this issue of EMBO Molecular Medicine, Zhang et al (2021) present the novel causative gene MOS in patients with the EEAF phenotype. The relationship between MOS variants and human EEAF is comprehensively established through a series of in vitro and in vivo experiments, thus clarifying the role of MOS during human oocyte maturation and early embryo development. These findings suggest that MOS is a new diagnostic marker of EEAF and is a potential therapeutic target for treatment of EEAF patients.