OPRK1 and obesity due to melanocortin 4 receptor deficiency: Fig 2I shows the expression of obesity-associated genes in the skin of 8-month old HFD animals relative to 8-month old chow counterparts. After 2 weeks on HFD, skin tissue increased Thrb (26-fold), Apoa4 (8.5-fold), and Sst (4-fold). After 6 months on HFD, skin tissue overexpressed Oprk1 (17-fold), Drd2 (11-fold), and Mc3r (11-fold) (Fig 2I).