CEACAM1 and hyperinsulinism: Using several genetically modified mouse models of loss- and gain-of-function of Ceacam1, we have demonstrated that CEACAM1 plays a critical role in promoting hepatic insulin clearance, and that its loss in the liver causes chronic hyperinsulinemia followed by systemic insulin resistance, altered lipid homeostasis, hepatosteatosis, and visceral obesity (5–7).