FABP4 and obesity due to melanocortin 4 receptor deficiency: Although mice deficient for either FABP4 or FABP5 demonstrate a modest phenotype due to their redundant function [6], [7], mice lacking both Fabp4 and Fabp5 (DKO mice) displayed a dramatic phenotype in their metabolism, including robust protection against diet-induced obesity, insulin resistance, type 2 diabetes, atherosclerosis, and fatty liver disease [8], [9].