PPARD and obesity due to melanocortin 4 receptor deficiency: Without detracting from the importance of PPARα andPPARδ (see below for PPARδ), the defining moment inthe explosive growth of the PPAR field has been the identificationof PPARγ as the high-affinity receptor of theinsulin-sensitizing thiazolidinedione (TZD) drugs [28, 29].The pivotal role of PPARγ in the adipocyte life cycle[30–34], combined with the blockbuster success ofits TZD ligands in treating type II diabetes [35, 36], generated widespread enthusiasm for the prospect of solving thecausal relationship between obesity and diabetes throughPPARγ research.