Pituitary adenomas are common tumors of the adenohypophysis which can cause 
considerable morbidity, due to excessive hormonal secretion or compression and 
local invasion of surrounding structures. The vast majority of pituitary 
adenomas occur sporadically. Altered gene expression is commonly detected but 
somatic mutations, epigenetic changes and abnormal microRNAs have also been 
described. Occurrence of GNAS mutations at a postzygotic stage lead to 
McCune-Albright syndrome (MAS), a disease causing endocrine hyperfunction and 
tumors in several organs, including the pituitary. Familial pituitary adenomas 
occur as part of a syndrome affecting other organs, such as in MEN1 or Carney 
complex, or occur with pituitary adenomas only as in familial isolated pituitary 
adenoma (FIPA). FIPA, an autosomal-dominant disease with variable penetrance, is 
explained in 20% of patients by germline mutations in the tumor suppressor aryl 
hydrocarbon receptor interacting protein(AIP), while no gene abnormality has 
been identified to date in the majority of the FIPA families. AIP 
mutation-positive patients have a characteristic clinical phenotype with usually 
young- or childhood-onset growth hormone (GH) and/or prolactin (PRL)-secreting 
adenomas and can be seen in cases with no apparent family history as well. 
Understanding the tumorigenic process in AIP-positive and AIP-negative FIPA 
patients could result in better diagnostic and treatment options for both 
familial and sporadic cases.