NPAS1 (neuronal PAS domain protein 1) is a basic helix-loop-helix PAS family transcription factor selectively expressed in the central nervous system beginning at embryonic day 15.5 12. NPAS1 functions as a master regulator of neuropsychiatric pathways through heterodimerization with ARNT to form transcriptional complexes that bind the core DNA sequence 5'-TACGTG-3' within hypoxia response elements 3. The protein contains four putative ligand-binding pockets, positioning it as a target for small-molecule drug development 3. Mechanistically, NPAS1 represses erythropoietin (EPO) expression in response to cellular oxygen levels during late CNS development 2. NPAS1 also represses cortical interneuron generation by suppressing the Arx enhancer in basal ganglia progenitors, reducing somatostatin-positive and VIP-positive interneuron populations while maintaining normal parvalbumin-positive neuron density 4. Genetically, NPAS1 loss-of-function mutations are linked to schizophrenia, autism spectrum disorders, and bipolar disorder 3. NPAS1 and NPAS3 act as master regulators controlling downstream neuropsychiatric risk genes including Fmr1 (fragile X syndrome) and Ube3a (Angelman syndrome), with NPAS1/3 targets showing increased human genetic burden for schizophrenia and intellectual disability 5. Understanding NPAS1 regulation provides insights into the shared molecular pathophysiology underlying diagnostically distinct neuropsychiatric conditions.