MC4R and hyperinsulinism: The hypothalamic expressed MC4R is a critical regulatorof energy homeostasis and food intake.31 Mutations of the mc4r gene have been associatedwith early onset obesity, hyperphagia, and hyperinsulinemia and havebeen linked to forms of monogenic and common obesity.4 A genome wide association study that involved half a millionpeople from UK Biobank has revealed 61 MC4R variants.