PPARD and obesity due to melanocortin 4 receptor deficiency: In contrast, few studies have focused on PPARδ, which is ubiquitously expressed, and the results have been inconsistent.12–14 Interaction between PPARδ and PPARα genotypes was demonstrated in a group of healthy men of normal weight.14 However, because obesity may result from the combined action of 2 or more single-nucleotide polymorphisms (SNPs), it is unclear whether corresponding gene–gene interactions exist among the 3 PPAR isoforms.