CDK2AP1 functions as a dual-action regulator of cell proliferation and epigenetic control. It directly inhibits cyclin-dependent kinase 2 (CDK2) and associates with DNA polymerase alpha/primase, suppressing DNA replication initiation 1. CDK2AP1 also serves as a component of the NuRD histone deacetylase complex, participating in chr12 remodeling and transcriptional regulation. During development, alternative isoforms with distinct functions are generated through species-specific retrotransposon promoters; a truncated isoform (Cdk2ap1ΔN) drives preimplantation proliferation, while canonical CDK2AP1 peaks in mid-gestation to suppress proliferation 2. In embryonic stem cells, CDK2AP1 is essential for differentiation by epigenetically silencing pluripotency factors 3. At the population level, CDK2AP1 represents a loss-of-function tolerant gene; however, clinical pathogenicity is evident across cancer contexts. Expression is reduced in breast cancer and oral cancers relative to normal tissue 4, yet elevated in hepatocellular carcinoma where it correlates with worse prognosis and immune infiltration 5. Conversely, CDK2AP1 knockdown in glioma cells inhibits growth and tumorigenesis 6. A common variant in the MPHOSPH9/CDK2AP1 locus associates with multiple sclerosis susceptibility through diminished CDK2AP1 expression 7, suggesting aberrant expression—rather than simple loss—underlies disease pathogenesis.