BANK1 (B cell scaffold protein with ankyrin repeats 1) is a B-cell-specific scaffold protein that plays critical roles in multiple B cell signaling pathways. Functionally, BANK1 promotes BCR-induced calcium mobilization from intracellular stores by facilitating Lyn-mediated phosphorylation of IP3 receptors, and participates in CD40-related and Toll-like receptor signaling 1. The protein acts as a molecular bridge, synergizing various signaling pathways within B cells 1. Genetically, BANK1 variants are strongly associated with systemic lupus erythematosus (SLE) susceptibility across multiple ethnic populations, with three SNPs (rs17266594, rs10516487, rs3733197) showing significant associations in meta-analyses of over 31,000 subjects 2. BANK1 variants are particularly associated with lupus nephritis in European ancestry populations, with evidence suggesting DNA methylation-based genetic regulation of BANK1 expression in this context 3. SNP rs10516487 also demonstrates epistatic interactions with the BLK gene in SLE pathogenesis 4. Beyond SLE, BANK1 variants associate with type 1 diabetes susceptibility 5 and contribute to shared immune function pathways in multi-organ fibrosis 6. Common variants alter BANK1 B cell expression levels, while rare variants modify effector binding during signaling 1. BANK1 represents a key genetic link in autoimmune disease pathogenesis through B cell dysregulation.