PTPN1 and obesity due to melanocortin 4 receptor deficiency: PTP1B-deficient mice are hypersensitive to insulin and resistant to obesity induced by a calorie-rich diet.5 For this reason, PTP1B has received attention over the last few years as a novel therapeutic target for the treatment of diabetes and obesity, and as such there are numerous inhibitors against PTP1B at various stages of development.6