In study 1 comprising hypopituitary subjects, we recorded a significant reduction of serum RBP4 concentrations in response to hyperinsulinemia during saline administration, and this observation is in line with the observations by Promintzer et al. (18) who reported a decrease of plasma RBP4 in response to a hyperinsulinemic–euglycemic clamp in overweight healthy insulin-sensitive as well as insulin-resistant adults. The gene discussed is INS; the disease is hyperinsulinism.