PNPLA2 and obesity due to melanocortin 4 receptor deficiency: Regarding lipid metabolism, the induction of both disorders, arthritis and obesity, alone or combined, promoted a decrease in the mRNA expression of genes involved in lipid accumulation (FAS and PPARγ) and an increase in the expression of genes related to lipolysis, such as HSL and ATGL (Figures 2F–I).