As in the case of FGF15, a single dose of rFGF4 rescued hyperinsulinemia in db/db mice (Supplementary Fig. 1b) but had no significant effect on either blood glucose or insulin levels in chow-fed wild type mice (Supplementary Fig. 1c, d), indicating that exogenous FGF4 does not stimulate pancreatic β-cell insulin release. The gene discussed is FGF4; the disease is hyperinsulinism.