Familial isolated pituitary adenoma (FIPA) is an autosomal dominant disease, 
characterized by low penetrance, early-onset disease, more invasive tumor 
growth, as well as somatotroph and lactotroph adenomas in most cases. It has 
been indicated that the aryl hydrocarbon receptor interacting protein (AIP) gene 
is a tumor suppressor gene. Many heterozygous mutations have been discovered in 
AIP in about 20% of FIPA families. However, the exact molecular mechanism by 
which its disfunction promotes tumorigenesis of pituitary is unclear.