AIP and pituitary tumor: Recently, other germline mutations involving four cyclin-dependent kinase inhibitor genes (CDKN1A/p15, CDKN2C/p18, CDKN2B/p21 and CDKN1B/p27) and, in patients with pituitary tumors, the AIP gene have been found in a minority of patients with clear MEN1 phenotype [3-5].