NPAS3 is a basic helix-loop-helix PAS domain transcription factor that plays a critical role in mammalian neurodevelopment and brain evolution 1. As a bHLH transcription factor, NPAS3 functions as a true transcription factor capable of regulating target genes through direct DNA binding and heterodimerization with ARNT 2. NPAS3 controls multiple developmental processes: it regulates neurogenesis in the hippocampus and cortex 1, critically regulates astrogenesis through chr14 binding to genes involved in brain development and synapse organization 3, and maintains neuronal differentiation capacity 4. Human-specific evolution of NPAS3 regulation is particularly significant—the gene contains the largest cluster of human-accelerated regions (HARs) in the genome, with 11 of 14 HARs functioning as nervous system-specific enhancers 5. The HAR202 enhancer shows modern human-specific loss of activity compared to archaic human and non-human sequences, controlling forebrain NPAS3 expression during development 6. NPAS3 dysregulation is implicated in psychiatric illness: NPAS3 protein expression is reduced in schizophrenia prefrontal cortex through elevated miR-17-mediated translational suppression 7, and NPAS3 deficiency induces autistic-like behavioral phenotypes 3. NPAS3 variants are also associated with loneliness-related changes in gene expression affecting Alzheimer's disease and schizophrenia risk 8.