Activating Mutations of GNAS in Canine Cortisol‐Secreting Adrenocortical Tumors

Background Cushing's syndrome or hypercortisolism is a common endocrinopathy in dogs. In approximately 15% of cases, the disorder is caused by adrenocorticotropin ( ACTH )‐independent hypersecretion of cortisol by an adrenocortical tumor ( AT ). Without other explanation, the cortisol hypersecretion has been referred to as autonomous. Objectives To investigate whether ACTH ‐independent hypersecretion of cortisol may be associated with aberrant activation of the melanocortin 2 receptor ( MC 2R)‐cyclic AMP ( cAMP )‐protein kinase A ( PKA ) pathway. Animals All analyses were performed on 44 cortisol‐secreting AT s (14 adenomas and 30 carcinomas) derived from dogs diagnosed with ACTH ‐independent hypercortisolism. Methods Mutation analysis was performed of genes encoding the stimulatory G protein alpha subunit ( GNAS ), MC 2R , and PKA regulatory subunit 1A ( PRKAR 1A ) in all AT s. Results Approximately one‐third of all AT s harbored an activating mutation of GNAS . Missense mutations, known to result in constitutive activation, were present in codon 201 in 11 AT s, in codon 203 (1 AT ), and in codon 227 (3 AT s). No functional mutations were found in MC 2R and PRKAR 1A . Conclusions and Clinical Importance Activation of cAMP signaling is a frequent event in canine cortisol‐secreting AT s and may play a crucial role in both ACTH ‐independent cortisol production and tumor formation. To the best of our knowledge, this is the first report of potentially causative mutations in canine cortisol‐secreting AT s.