From the First Case Reports to KDM1A Identification: 35 Years of Food (GIP)-Dependent Cushing's Syndrome.

Food-dependent Cushing's syndrome (FDCS) is a rare presentation of hypercortisolism from adrenal origin, mostly observed in primary bilateral macronodular adrenal hyperplasia (PBMAH) but also in some cases of unilateral adrenocortical adenoma. FDCS is mediated by the aberrant expression of glucose-dependent insulinotropic peptide (GIP) receptor (GIPR) in adrenocortical cells. GIP, secreted by duodenal K cells after food intake, binds to its ectopic adrenal receptor, and stimulates cortisol synthesis following meals. FDCS was first described more than 35 years ago, and its genetic cause in PBMAH has been recently elucidated: inactivation by germline heterozygous pathogenic variants is constantly associated with a loss-of-heterozygosity of the short arm of chromosome 1, containing the locus. This causes biallelic inactivation of , resulting in the GIPR overexpression in the adrenal cortex. These new insights allow us to propose the genetic screening to all PBMAH patients with signs of FDCS (low fasting cortisol that increases after a mixed meal or oral glucose load) and to all first-degree relatives of variant carriers. Given that is a tumor suppressor gene that has also been associated with monoclonal gammopathy of uncertain significance and multiple myeloma, the investigation of FDCS in the diagnostic management of patients with PBMAH and further genetic testing and screening for malignancies should be encouraged.