KLB and obesity due to melanocortin 4 receptor deficiency: Abnormally high FGF21 levels are considered a marker of disturbed metabolism in non-HIV-infected patients with obesity, diabetes, or congenital lipodystrophy (15, 16, 42), whereas KLB repression is associated with an impairment of glucose uptake and other health effects mediated by FGF21 (27).