SLC4A2 (solute carrier family 4 member 2) encodes an anion exchanger that mediates sodium-independent, electroneutral exchange of chloride for bicarbonate ions across the cell membrane 12. The gene spans over 17 kb with 23 exons and contains multiple transcription initiation sites, with tissue-specific expression driven by alternate promoters regulated by transcription factors such as HNF1alpha 34. Primary physiological functions include intracellular pH regulation and control of cell volume through anion exchange 5. SLC4A2 plays a critical role in osteoclast differentiation and function, where it is exclusively expressed at the contra-lacunar membrane and participates in bone resorption through pH-dependent control of calpain-dependent actin cytoskeleton organization 25. Clinically, biallelic loss-of-function mutations in SLC4A2 cause autosomal recessive osteopetrosis (osteopetrosis, Ikegawa type), characterized by increased bone density due to impaired osteoclast-mediated bone resorption and defective podosome belt formation 25. In primary biliary cholangitis, disease-specific promoter hypermethylation and downregulation of SLC4A2 expression contribute to pathogenesis 6. Recent evidence suggests SLC4A2 upregulation promotes colorectal cancer progression through epithelial-mesenchymal transition activation 7.