PTPN1/2 are well characterized as regulators of leptin and insulin signaling, and their dysregulations have been linked to metabolic disorders, including diabetes and obesity (Elchebly et al, 1999; Cheng et al, 2002; Zabolotny et al, 2002). Here, PTPN1 is linked to obesity due to melanocortin 4 receptor deficiency.