Similar to our IGHD subjects, little mice (also carrying a homozygous GHRHR mutation like our subjects) (27) and mice with GH receptor gene ablation (GHRKO) (3) are hypersensitive to insulin, but have IGT due to a reduced number of pancreatic β cells and reduced insulin secretion, probably due to reduced pancreatic β-cell mass. Here, INS is linked to isolated congenital growth hormone deficiency.