The decrease of leptin level due to fasting or genetic leptin deficiency led to the reduced expression of proopiomelanocortin gene and to the increased expression of AgRP gene [54], and leptin infusion, on the contrary, increased the hypothalamic content of proopiomelanocortin and MC4R and inhibited the production of AgRP [55]. This evidence concerns the gene AGRP and hyperinsulinemic hypoglycemia, familial, 4.