CCDC91 (coiled-coil domain containing 91) is a multifunctional protein primarily involved in intracellular membrane trafficking and bone development. The protein regulates membrane traffic through the trans-Golgi network and functions in cooperation with GGA proteins for sorting hydrolases to lysosomes, as supported by its cellular localization and functional studies 1. CCDC91 plays a critical role in bone biology, where genetic variants are associated with hip bone geometry, bone mineral density, and ossification disorders 23. A novel CCDC91 isoform functions as a competitive endogenous RNA, sequestering MIR890 to upregulate RUNX2 expression and promote osteogenic differentiation 4. Loss-of-function mutations in CCDC91 cause autosomal-dominant acrokeratoelastoidosis through impaired elastin transport, resulting in tropoelastin accumulation in the Golgi and abnormal extracellular aggregates 1. In disease contexts, CCDC91 shows oncogenic properties in hepatocellular carcinoma, where HBV integration upregulates its expression, leading to enhanced aerobic glycolysis through LDHA activation 5. The gene also serves as part of a T-cell-derived signature distinguishing SARS-CoV-2 infections from other respiratory viruses 6 and contributes to white matter microstructure regulation in the brain 7.