AHR may also have AIP-independent roles in pituitary tumorigenesis as AHR but not AIP expression is reduced in GNAS-mutated somatotrophinomas, and AHR activation increases the transcription of CDKN1B, which is another tumour suppressor gene implicated in pituitary and other endocrine tumours [10]. The gene discussed is GNAS; the disease is growth hormone-producing pituitary gland adenoma.