Germline mutations of aryl hydrocarbon receptor interacting protein (AIP), a gene coding for a cytoplasmic interaction partner of aryl hydrocarbon receptor (AHR) (also known as dioxin receptor), were recently described to cause low-penetrance pituitary adenoma predisposition (PAP) (Vierimaa et al, 2006). This evidence concerns the gene AIP and pituitary gland adenoma.