APOE and obesity due to melanocortin 4 receptor deficiency: Along the same line, mice expressing human APOE3 in place of mouse Apoe (apoe3knock-in) fed the standard western-type diet (21% fat) for 24 weeks were more sensitive to diet-induced obesity and related metabolic dysfunctions than wild-type C57BL/6 mice, while apoe-/- mice were resistant to these conditions[44].