Despite the multiple salutatory effects of FGF21 on glucose and lipid metabolism in animals, circulating FGF21 levels are elevated in obese subjects [5, 6] and patients with impaired glucose tolerance [7], type 2 diabetes mellitus [5, 7, 8], dyslipidemia [9], and nonalcoholic fatty liver disease (NAFLD) [10, 11]. The gene discussed is FGF21; the disease is diabetes mellitus.