This unique disturbance of the cAMP-PDE pathway observed in the majority of <i>AIP</i>-mutation positive adenomas could contribute to their well-described poor response to somatostatin analogs and may support a role in tumorigenesis.
No significant difference was observed in AIP mRNA expression between tumors with low or high AIP protein expression suggesting post-transcriptional regulation. miR-34a was highly expressed in low AIP protein samples compared high AIP protein adenomas and miR-34a levels were inversely correlated with response to SSA therapy. miR-34a inhibited the luciferase-AIP-3'UTR construct, suggesting that miR-34a binds to AIP-3'UTR.
AIP variants were detected in 3% of the 127 patients, comprising four of 48 patients with acromegaly (8%), 0 of 43 with prolactinomas, 0 of the 20 patients with non-functioning adenomas, 0 of 15 with corticotroph adenomas and 0 of one with a thyrotroph adenomas.
AIP mutations are usually associated with somatotropinomas, but prolactinomas, nonfunctioning pituitary adenomas, Cushing disease, and other infrequent clinical adenoma types can also occur.
AIP mutations cause a low penetrance autosomal dominant disease with often a distinct phenotype characterized by young-onset, aggressive, large GH, mixed GH and PRL or PRL-secreting adenomas.
AIP mutations were detected in 16 (3.6%) of the 443 patients, comprising six of 148 patients with acromegaly (4.1%), six of 132 patients with prolactinomas (4.5%), one of 113 patients with nonfunctioning adenomas (0.9%), three of 44 patients with corticotropic adenomas (6.8%), and none of the six patients with thyrotropic adenomas.
Patients with mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene are characterized by young-onset somatotroph or lactotroph macroadenomas, while in the other, larger group of FIPA patients with typically adult-onset disease and more varied adenoma types, no causative gene(s) has been identified.
In addition, we summarize the clinical features of IFS families with AIP mutations: The adenomas are diagnosed at a young age and are larger than in IFS patients without AIP mutations or in sporadic somatotropinomas, indicating more aggressive disease.
Though AIP mutation-positive individuals with prolactin-, mixed growth hormone/prolactin-, and ACTH-producing pituitary adenomas as well as non-secreting pituitary adenomas have been reported, most mutation-positive patients have had growth hormone-producing adenomas diagnosed at relatively young age.
Feasibility of AIP immunohistochemistry (IHC) as a prescreening tool was tested in 50 adenomas: 12 AIP mutation-positive versus 38 mutation-negative pituitary tumors.