The discrepant data on the connection between FGF21 and thyroid function might be partially explained by the hepatic damage resulting in FGF21 elevation being often associated with hyperthyroidism, as clarified in the study of Xiao et al. [30], while in subclinical hypothyroidism, FGF21 might be elevated as an adaptive mechanism to the accompanying obesity [22]. The gene discussed is FGF21; the disease is obesity due to melanocortin 4 receptor deficiency.