ADIPOR1 and obesity due to melanocortin 4 receptor deficiency: miR-221 may contribute to the development of the insulin resistance that typically accompanies obesity by regulating the peroxisome proliferator activated receptor (PPAR) signaling pathway and directly down-regulating adiponectin receptor 1 (ADIPOR1) and ETS proto-oncogene 1, transcription factor (ETS1) [25].