Low-dose tests (1 mg overnight, i.e., overnight suppression test, OST, or 2 mg over 2 days) are used to identify patients with Cushing’s syndrome whereas high-dose dexamethasone tests (8 or 16 mg) are employed to distinguish between pituitary and ectopic ACTH secretion or to evoke a paradoxical cortisol response in adrenal nodular dysplasia. This evidence concerns the gene POMC and Cushing syndrome.