PPARG and obesity due to melanocortin 4 receptor deficiency: Subsequent candidate gene studies (based on an approach assessing the association between an allele or a group of alleles of a gene potentially involved in a disease and the disease itself [39]) then led to the hypothesis that the peroxisome proliferator-activated receptor gamma (PPAR-γ) may represent a predisposing factor for obesity and insulin resistance [38,40,41].