NRGN encodes neurogranin, a brain-specific 78-amino acid postsynaptic protein that functions as a calmodulin-binding substrate in calcium-independent signaling cascades 1. The protein acts as a 'third messenger' in protein kinase C-mediated pathways during synaptic development and plasticity, particularly in telencephalic neurons 1. NRGN expression is regulated by thyroid hormone through a T3-responsive element in its first intron, suggesting involvement in thyroid hormone-dependent neuronal processes 2. The gene shows significant clinical relevance in neuropsychiatric and neurodegenerative diseases. Genetic variants, particularly rs12807809, are associated with schizophrenia risk and altered hippocampal functional connectivity 34. Reduced NRGN expression correlates with the high-risk haplotype and may contribute to schizophrenia pathophysiology 4. In Alzheimer's disease, NRGN serves as a neurodegeneration biomarker, with elevated levels in neuron-derived extracellular vesicles correlating with disease progression and cognitive decline 56. Additionally, NRGN appears to modulate immune responses in hepatocellular carcinoma by promoting TGF-β1 secretion, suggesting broader roles beyond neuronal function 7. These findings establish NRGN as both a critical synaptic regulatory protein and a clinically relevant biomarker across multiple disease contexts.