Genome-wide association studies (GWAS) have identified multiple loci associated with body mass index (BMI), such as fat mass and obesity-associated (FTO), uncoupling protein (UCP), brain-derived neurotrophic factor (BDNF), beta-3 adrenergic receptor (ADRB3), neuronal growth regulator 1 (NEGR1), proprotein convertase subtilisin/kexin type 2 (PCSK2), and peroxisome proliferator-activated receptor gamma (PPARG) (Table 2). The gene discussed is NEGR1; the disease is obesity due to melanocortin 4 receptor deficiency.