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Mirella Hage, Clément Janot, Sylvie Salenave, Philippe Chanson, and Peter Kamenický

To gain more insight on the pathogenesis of somatotroph pituitary adenomas, recent studies have focused on a subgroup of patients with acromegaly displaying a paradoxical growth hormone (GH) response during oral glucose tolerance test (OGTT). The paradoxical rise of GH after oral glucose intake occurs in about one-third of acromegaly patients and has been pathogenetically linked, by analogy to glucose-dependent insulinotropic polypeptide (GIP)-dependent Cushing's syndrome, to the ectopic expression of GIP receptor (GIPR) in somatotroph adenoma cells. GIPR-expressing adenomas are negative for activating GNAS gene mutations and display distinct cytogenetic and DNA methylation profiles, highlighting their unique molecular pathogenesis. Acromegaly patients with a paradoxical GH response pattern seem to display higher insulin-like growth factor-1 (IGF-1) concentrations and harbour smaller adenomas that are more often of the densely granulated phenotype. They seem also to show a better response to somatostatin receptor ligands. In addition, persistent paradoxical GH response after surgery may be a biological marker of the residual disease postoperatively. Targeted therapy to antagonize GIP receptor on GIPR-expressing somatotroph adenomas could be a new treatment approach for acromegaly patients with a paradoxical pattern of GH response to OGTT.

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Anne-Lise Lecoq, Jérôme Bouligand, Mirella Hage, Laure Cazabat, Sylvie Salenave, Agnès Linglart, Jacques Young, Anne Guiochon-Mantel, Philippe Chanson, and Peter Kamenický

Context

Recently, germline and somatic GPR101 p.(E308D) mutation was found in patients with isolated acromegaly. It is not known whether GPR101 point mutations are associated with other histological types of pituitary adenoma.

Objective

We sought germline GPR101 mutations in patients with sporadic pituitary adenomas, and compared the phenotypes of GPR101 mutation carriers and AIP mutation carriers.

Design

An observational cohort study performed between 2007 and 2014 in a single referral center.

Participants

This prospective study involved 766 unselected patients (413 women) with sporadic pituitary adenomas of all histotypes.

Methods

Entire GPR101 and AIP coding sequence were screened for germline mutations.

Results

Twelve patients (1.6%) were found to carry the GPR101 p.(E308D) mutation or rare GPR101 variants. The minor allele frequency of the GPR101 mutation and variants was higher in patients with pituitary adenomas than in unaffected individuals included in the Exome Aggregation Consortium database. Three of the six patients with the GPR101 p.(E308D) mutation had adult-onset acromegaly, two had adrenocorticotropin-secreting adenomas, and one had a nonfunctioning macroadenoma. Six patients carried rare GPR101 variants. Germline AIP mutations or rare AIP variants were identified in 32 patients (4.2%). AIP mutation carriers were younger at diagnosis than GPR101 mutation carriers and non carriers. None of the patients harbored mutations in both the GPR101 and AIP genes.

Conclusion

Germline GPR101 mutations are very rare in patients with sporadic pituitary adenomas of various histotypes. No digenism with AIP was identified. Further studies are required to establish whether and how genetic variation in GPR101 gene contributes to pituitary tumorigenesis.