CCDC121 (coiled-coil domain containing 121) is a protein-coding gene located on chromosome 2 with putative protein binding function based on Gene Ontology annotations. Limited functional data are available from the provided literature. CCDC121 has been identified as a mutated gene in gastric cancer peritoneal metastasis, appearing in the COSMIC database 1. In the context of periodontal disease susceptibility, the murine orthologue Ccdc121 was identified within a quantitative trait locus (Perio3) associated with alveolar bone loss in response to experimental periodontal infection in mice; however, the human orthologue showed only nominal association with chr2 periodontitis and no definitive functional role was established 2. Additionally, CCDC121 has been characterized as a marker gene specific for inner ear stem cells or progenitor cells during in vitro differentiation, where it was co-expressed with Gdf10 3. The gene's coiled-coil domain suggests potential involvement in protein-protein interactions, though the specific molecular mechanisms remain unclear. Further investigation is needed to establish CCDC121's precise biological functions and clinical significance in cancer, periodontal disease, and inner ear biology.