GNAS and adrenal cortex neoplasm: Indeed, CPAs are a leading cause of adrenocortical tumours, the majority of which are caused by somatic mutations in genes such as GNAS or PRKACA. 2,3 These genes, which, when mutated, result in constitutive activation of the protein kinase A (PKA) pathway to induce cell proliferation and autonomous steroidogenesis,2 thereby leading to the development of adrenocorticotropic hormone (ACTH)-independent Cushing's syndrome (CS) and mild autonomic cortisol excess (MACE).