Genetics of Cushing's syndrome.

Cushing's syndrome (CS) is characterized by pathologically elevated free glucocorticoid levels. Endogenous hypercortisolism is usually due to ACTH-secreting pituitary corticotropic adenomas and less often due to ectopic ACTH-secreting neuroendocrine neoplasms or ACTH-independent adrenal cortisol hypersecretion. CS is a serious chronic disease leading to a several-fold increase in cardiovascular morbidity and mortality. Multiple genetic alterations have been described in the setting of sporadic corticotropinoma formation. Changes in the expression profiles have been demonstrated in growth factors and their receptors, cell-cycle regulators and in various genes related to hormonal gene transcription, synthesis and secretion. Sporadic adrenal adenomas and carcinomas may demonstrate dysfunction in genes such as TP53 among others. Cushing's disease can be an inherited condition also. Multiple endocrine neoplasia type 1 (MEN1) and familial isolated pituitary adenomas (FIPA) together account for 5% of pituitary adenomas. Cushing's disease occurs infrequently in an inherited setting in both of these conditions. To date only 2 cases of Cushing's disease have been described in association with mutations in AIP. One case of Cushing's disease has been reported as part of MEN4, a rare MEN1-like syndrome due to mutation in the CDKN1B gene. Carney complex (CNC) due to PRKAR1A mutations in most cases is associated with CS, mainly as a cause of bilateral adrenal hyperplasia. The cAMP signaling pathway is affected in this setting. In recent times the involvement of genes such as PDE11A, PDE8B and others have expanded the spectrum of the genetic pathophysiology of CS.