HMG20A is a chr15-associated protein encoded on chromosome 15 that functions as a transcriptional regulator through multiple mechanisms. As a DNA-binding HMG-box protein 1, HMG20A plays a central role in neuronal differentiation by overcoming REST-mediated repression and recruiting histone methyltransferase KMT2A/MLL1 to activate neuronal-specific genes. HMG20A interacts with calcium-dependent S100 proteins (S100A1, S100A2, S100A6, S100B) via its C-terminal region 2, linking calcium signaling to its regulatory functions. Beyond neuronal development, HMG20A coordinates metabolic and immune processes: it inhibits adipogenesis through transcriptional and epigenetic regulation of MEF2C 3, maintains astrocyte survival and reactive astrogliosis to preserve neuronal integrity under metabolic stress 4, and is essential for pancreatic beta-cell functional maturity and glucose-stimulated insulin secretion 5. HMG20A forms a complex with histone reader PHF14 to modulate TGFβ and Hippo signaling pathways affecting epithelial-mesenchymal plasticity 6. Clinically, HMG20A associates with type 2 diabetes risk; the rs7119 SNP reduces HMG20A expression 5, and dysregulation contributes to lung cancer stemness through CREB-mediated signaling 7. Mutations in HMG20A are linked to neurodevelopmental disorders as a component of the MeCP2-interacting TCF20/PHF14 chr15 complex 8.