AIP and familial isolated pituitary adenoma: In the transition age, the most frequent cause of acro-gigantism in patients with FIPA is the presence of loss-of-function mutations in the gene coding for the aryl hydrocarbon receptor-interacting protein (AIP) [54], which account for 29% of cases of pituitary gigantism, as reported in the largest multicentre European study to date (208 patients with gigantism) [39].