SLC35A1 encodes a CMP-sialic acid transporter that functions as an antiporter, exchanging CMP-sialic acid for CMP and other pyrimidine nucleotides (AMP, UMP) to facilitate transport of CMP-sialic acid from the cytosol into the Golgi apparatus 123. The transporter contains three substrate-binding pockets—nucleobase, middle, and sugar pockets—with specific residues including Y214 in the nucleobase pocket critical for discriminating cytosine from uracil 4. SLC35A1 is essential for sialylation, the terminal glycosylation of proteins and lipids, which impacts multiple biological processes including receptor expression and viral susceptibility 56. Mutations in SLC35A1 cause congenital disorder of glycosylation 2F (SLC35A1-CDG), characterized by altered cellular glycosylation, lipid, and energy metabolism even when serum CDG markers appear normal 6. The transporter plays a critical role in viral pathogenesis: SLC35A1 knockout reduces surface sialic acid expression, decreasing susceptibility to influenza A virus, porcine deltacoronavirus, Newcastle disease virus, and porcine epidemic diarrhea virus by impairing viral adsorption and entry 78910. Additionally, SLC35A1 deficiency causes thrombocytopenia through impaired megakaryocytopoiesis and increased platelet clearance 5, and SLC35A1 knockout enhances AAV9 transduction efficiency by unmasking terminal galactose receptors 11.