NCAN (neurocan) is a chondroitin sulfate proteoglycan that modulates neuronal development and brain structure. During development, NCAN binds to neural cell adhesion molecules (NG-CAM and N-CAM) and hyaluronic acid to regulate neuronal adhesion and neurite growth, functioning as a component of the perineuronal net and extracellular matrix 1. NCAN variants significantly associate with brain structure variation, particularly in white matter volume of temporoparietal and inferior frontal regions in adults, and grey matter volumes in infants 2. The protein shows robust associations with cognitive function, with plasma NCAN levels linked to digit symbol substitution test performance, partially mediated through structural brain phenotypes 3. NCAN genetic variants contribute to bipolar disorder susceptibility as a polygenic risk factor 4. Elevated circulating NCAN levels associate with depression-like behavior in primate models and may serve as a potential biomarker for major depressive disorder through inflammatory pathways 5. Additionally, NCAN variants show associations with serum lipid levels in population studies 6. Proteomic analyses identify NCAN among the most significantly associated proteins with brain structure variation, implicating roles in neurogenesis and neuronal function 7. The gene represents a candidate locus for developmental dyslexia 2, suggesting critical involvement in neurodevelopmental processes.