PPARG and obesity due to melanocortin 4 receptor deficiency: Also, the peroxisome proliferator-activated receptor-γ (PPARγ) gene, which has been extensively studied for GEI related to obesity and type 2 diabetes [32, 43], was reported to have a diet-related effect on risk to obesity with the Pro12 allele being associated with increased adiposity in a high-fat diet group [44].