Corticotropin (ACTH) acts by bindin

Corticotropin (ACTH) acts by binding to a specific cell-surface receptor, the melanocortin receptor-2 (MC2R) [3]. ACTH upregulates expression of these receptors, thereby increasing the steroidogenic response to further ACTH stimulation [4].Failure of MC2R to activate in response to ACTH causes familial glucocorticoid deficiency (FGD), a rare autosomal recessive disorder characterized by severe cortisol deficiency with high plasma ACTH concentrations and normal mineralocorticoid levels. MC2R mutations resulting in effective loss of the receptor function are responsible for FGD type 1, which accounts for up to 25 percent of all FGD cases [5]. (See "Causes and clinical manifestations of primary adrenal insufficiency in children", section on 'Familial glucocorticoid deficiency'.)