NHLH2 is a basic helix-loop-helix transcription factor that functions as a master regulator of energy homeostasis and reproductive function 1. It binds E-box motifs in target gene promoters, including KISS1, PCSK1, and MC4R, acting as a transcriptional activator to coordinate hypothalamic neuropeptide expression 2. NHLH2 expression responds to energy availability signals, with high levels during energy surplus and reduced expression during food deprivation, positioning it centrally in leptin-responsive pathways that regulate prohormone convertase expression and downstream neuropeptide synthesis 1. The transcription factor is enriched in hypothalamic Kiss1 neurons, where it regulates kisspeptin and neurokinin B synthesis, controlling gonadotropin-releasing hormone release and reproductive timing in a sex-specific manner 2. NHLH2 is also expressed in pro-opiomelanocortin neurons, where it regulates motivated exercise behavior 3. Functionally, NHLH2 knockout mice exhibit adult-onset obesity with reduced exercise motivation and fertility defects. In humans, NHLH2 mutations cause hypogonadotropic hypogonadism without anosmia 4. Notably, NHLH2 mRNA stability is post-transcriptionally regulated by SNORD116, a non-coding RNA deleted in Prader-Willi syndrome, explaining reduced NHLH2 expression in PWS patients 5. Multiple missense variants cluster around the DNA-binding domain and may contribute to obesity and reproductive phenotypes 6.