SLC6A4 and obesity due to melanocortin 4 receptor deficiency: The common targets of obesity, T2DM, and NAFLD are solute carrier family 6 member 4 (SLC6A4), acetylcholinesterase (ACHE), opioid receptor Mu 1 (OPRM1), and glycogen synthase kinase 3 beta (GSK3B).