The genetic causes of familial acromegaly and pituitary gigantism include variants in established pituitary adenoma predisposition genes (AIP, especially, but also MEN1, CDKN1B, MAX, and PRKAR1A), X-linked acrogigantism due to Xq26.3 microduplications, and McCune-Albright syndrome due to postzygotic gain-of-function GNAS variants. Here, GNAS is linked to pituitary gland adenoma.