KLB and obesity due to melanocortin 4 receptor deficiency: Furthermore, in adipose tissue, others have reported decreased expression of the FGF21 receptor and/or its co-receptor KLB in diabetes and obesity, suggesting a state of FGF21 resistance (Fisher et al., 2010; Nygaard et al., 2014; Gallego-Escuredo et al., 2015; So and Leung, 2016).