FGF21 and obesity due to melanocortin 4 receptor deficiency: Circulating FGF-21 levels were positively correlated with obesity-related metabolic complications (Zhang et al., 2008), renal function (Lin et al., 2011), atherosclerosis (Chow et al., 2013), and hypertension (Semba et al., 2013), indicating that FGF-21 may be used as a biomarker in metabolic or even non-metabolic diseases.