The insulin resistance signaling pathway is closely related to diabetes, metabolic syndrome and obesity and is also closely related to the activities of phosphoenolpyruvate carboxykinase 1 (PCK1) and solute carrier family 2 member 4/GLUT4 (SLC2A4) [62,63]. Here, SLC4A2 is linked to obesity due to melanocortin 4 receptor deficiency.