MOS (MOS proto-oncogene, serine/threonine kinase) encodes a serine/threonine protein kinase that plays a crucial role in female fertility by regulating oocyte maturation and early embryonic development. The protein functions as an activator of the MAPK signaling cascade, specifically phosphorylating MEK1/2 to activate ERK1/2 signaling pathways essential for proper oocyte maturation 1. MOS is required for asymmetric oocyte division, as mutations lead to symmetric division and production of abnormally large first polar bodies 1. Biallelic variants in MOS cause female infertility through multiple mechanisms, including oocyte maturation arrest, early embryonic arrest and fragmentation (EEAF), and abnormal polar body formation 12. The clinical significance of MOS variants is substantial, as they represent a novel diagnostic marker for unexplained female infertility characterized by specific oocyte morphological abnormalities 2. Patients with MOS mutations display recurrent IVF/ICSI failures due to defective oocyte maturation and early embryonic developmental arrest 1. The gene is located on chromosome 8.1-21.3 and may have broader implications in tumorigenesis, as this chr8 region is frequently amplified in breast cancer 3.