PTPN1 and obesity due to melanocortin 4 receptor deficiency: Recently, that has been an increasing number of reports which have demonstrated that PTPN1 is involved in human disorders such as diabetes, obesity, and cancer.36, 37, 38 However, different research results have demonstrated that PTPN1 plays a dual role in malignant tumors, which depends on the substrate expression level of PTPN1 in distinct cells.28