TMEM18 is a highly conserved transmembrane protein with critical roles in energy homeostasis and adipose tissue development 1. The gene encodes a transcription repressor with four transmembrane domains that physically interacts with nuclear pore complex components 2. In the central nervous system, TMEM18 expression in the hypothalamic paraventricular nucleus is dynamically regulated by nutritional state 2. Functionally, TMEM18 promotes healthy adipogenesis by activating PPARG signaling, particularly PPARG1 promoter activity, which is suppressed by inflammatory stimuli 3. At the systems level, TMEM18 regulates insulin and glucagon-like signaling, affecting substrate metabolism 4. Clinically, TMEM18 polymorphisms—particularly rs6548238, rs939583, and rs1879523—are among the strongest genetic associations with obesity risk, with ethnic and age-dependent effects 5. Germline loss of Tmem18 in mice increases body weight through elevated food intake, while selective overexpression in the PVN reduces food intake and increases energy expenditure 2. Importantly, lifestyle factors including physical activity and wine consumption significantly attenuate obesity risk in carriers of TMEM18 risk variants 6. TMEM18 variants also associate with type 2 diabetes risk independent of BMI and influence age at diabetes diagnosis 7. Rare paternal deletions encompassing TMEM18 cause early-onset obesity with hyperphagia 8.