BST1 (bone marrow stromal cell antigen 1) is a transmembrane enzyme that catalyzes the synthesis of cyclic ADP-ribose (cADPR) from NAD+ and its hydrolysis to ADP-ribose, functioning as a NAD+-dependent signaling molecule. cADPR serves as an endogenous second messenger that regulates calcium release from intracellular stores, enabling calcium-mediated signaling and cellular responses including immune cell activation and migration. BST1 also displays glycohydrolase activity on nicotinamide riboside metabolism and base-exchange activities connecting NAD+ biosynthetic pathways 1. The gene regulates mesenchymal stem cell self-renewal, migration, and osteogenic differentiation through the SCRG1/BST1 signaling axis 2. BST1 variants are genetically associated with Parkinson disease age at onset 3, isolated REM sleep behavior disorder (driven by rare loss-of-function nonsynonymous variants) 4, and autism spectrum disorders 5. Emerging clinical evidence identifies BST1 as a potential biomarker for response to chemoimmunotherapy in unresectable stage III non-small cell lung cancer 6 and as a diagnostic marker in acute-on-chr4 liver failure, where elevated BST1 expression correlates with neutrophil extracellular trap-related immune dysregulation 7.