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Alper Gürlek, Niki Karavitaki, Olaf Ansorge and John A H Wass

Prolactinoma is the most common pituitary tumour in adults. Macroprolactinomas, particularly in men, may occasionally exhibit a very aggressive clinical course as evidenced by progressive growth, invasion through bone into the sphenoid sinus, cavernous sinus, suprasellar region or the nasopharynx. Some may even progress to pituitary carcinoma with craniospinal or systemic metastases. Aggressive tumours have low cure rates despite appropriate medical and surgical treatment. The mechanisms underlying this aggressive biological behaviour have not yet been fully clarified. Recent immunohistochemical, molecular and genetic studies have provided some insight in this respect. Invasive prolactinomas may be associated with a high Ki-67/MIB-1 labelling index indicating increased cell proliferation, although this is not a universal finding. The AA polymorphism in the cyclin adenine (A)/guanine (G) gene is more frequently detected in invasive prolactinomas. Increased expression of the polysialylated neural cell adhesion molecule (NCAM) and reduced expression of the E-cadherin/catenin complex implies a contribution of altered cell-to-cell adhesion and cellular migration. Extracellular matrix components (ECM), matrix metalloproteinases (MMPs) and their inhibitors play important roles in the context of angiogenesis and invasion. The induction of fibroblast growth factor and vascular endothelial growth factor via oestrogen-induced overexpression of novel genes (PTTG, hst and Edpm5) enhance cell growth, proliferation and angiogenesis contributing to invasiveness in prolactinomas. Although mutations in proto-oncogenes like Ras are uncommon, loss of tumour suppressor genes at loci 11q13, 13q12–14, 10q and 1p seem to be associated with invasiveness. Of the described mechanisms, only reduced E-cadherin/catenin expression and overexpression of hst gene seem to be relatively specific markers for prolactinoma invasiveness compared with other pituitary adenomas. Further research is needed to clarify the molecular mechanisms behind the aggressive course of some prolactinomas to predict those with a potentially poor clinical outcome, and to devise treatments that will eventually enable the cure of these challenging tumours.

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Sarah Larkin, Raghava Reddy, Niki Karavitaki, Simon Cudlip, John Wass and Olaf Ansorge

Objective

Somatotroph adenomas causing acromegaly are histologically classified into densely granulated (DG) and sparsely granulated (SG) subtypes with different morphology, clinical characteristics and treatment outcomes. Granulation pattern has been reported to co-segregate with a recurrent mutation at codon 49 in growth hormone receptor (GHR) and GSP oncogene. This study examines response to the octreotide suppression test (OST) in relation to granulation pattern and mutation in GHR and GSP.

Design

This is a retrospective, single-centre study of 52 patients with pathologically confirmed somatotroph adenoma who were naïve to medical therapy presenting between January 2001 and October 2010.

Methods

Clinical, radiological and hormonal data at diagnosis were recorded. GHR and GSP were genotyped, granulation pattern determined and response to the OST measured.

Results

SG adenomas were larger (P=0.038), occurred in younger patients (P=0.029), were more common in females (P=0.026) and were more invasive (P<0.0001 and P=0.001), with diminished responses to the OST (P=0.007) compared with DG adenomas. GSP mutation was unrelated to granulation pattern but associated with smaller tumours (P=0.027), producing more GH (P=0.048) that responded better to the OST (P=0.022). Codon 49 of GHR was not mutated.

Conclusions

Adenoma histological phenotype, not genotype, corresponds to clinical and biochemical characteristics and response to the OST. SG adenomas constitute a clinically more unfavourable subtype but are not associated with GHR mutations in our series. Ascertainment of the adenoma subtype may become an important consideration in the management of acromegaly.

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Sarah J Larkin, Francesco Ferraù, Niki Karavitaki, Laura C Hernández-Ramírez, Olaf Ansorge, Ashley B Grossman and Márta Korbonits

Objective

The pathogenetic mechanisms of sporadic somatotroph adenomas are not well understood, but derangements of the cAMP pathway have been implicated. Recent studies have identified L206R mutations in the alpha catalytic subunit of protein kinase A (PRKACA) in cortisol-producing adrenocortical adenomas and amplification of the beta catalytic subunit of protein kinase A PRKACB in acromegaly associated with Carney complex. Given that both adrenocortical adenomas and somatotroph adenomas are known to be reliant on the cAMP signalling pathway, we sought to determine the relevance of the L206R mutation in both PRKACA and PRKACB for the pathogenesis of sporadic somatotroph adenomas.

Design

Somatotroph adenoma specimens, both frozen and formalin-fixed, from patients who underwent surgery for their acromegaly between 1995 and 2012, were used in the study.

Methods

The DNA sequence at codon 206 of PRKACA and PRKACB was determined by PCR amplification and sequencing. The results were compared with patient characteristics, the mutational status of the GNAS complex locus and the tumour granulation pattern.

Results

No mutations at codon 206 of PRKACA or PRKACB were found in a total of 92 specimens, comprising both WT and mutant GNAS cases, and densely, sparsely and mixed granulation patterns.

Conclusions

It is unlikely that mutation at this locus is involved in the pathogenesis of sporadic somatotroph adenoma; however, gene amplification or mutations at other loci or in other components of the cAMP signalling pathway, while unlikely, cannot be ruled out.

Open access

Roberto Salvatori, Serban Radian, Yoan Diekmann, Donato Iacovazzo, Alessia David, Plamena Gabrovska, Giorgia Grassi, Anna-Marie Bussell, Karen Stals, Astrid Weber, Richard Quinton, Elizabeth C Crowne, Valentina Corazzini, Lou Metherell, Tara Kearney, Daniel Du Plessis, Ajay Kumar Sinha, Atik Baborie, Anne-Lise Lecoq, Philippe Chanson, Olaf Ansorge, Sian Ellard, Peter J Trainer, David Balding, Mark G Thomas and Márta Korbonits

Objective

Mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene are associated with pituitary adenoma, acromegaly and gigantism. Identical alleles in unrelated pedigrees could be inherited from a common ancestor or result from recurrent mutation events.

Design and methods

Observational, inferential and experimental study, including: AIP mutation testing; reconstruction of 14 AIP-region (8.3 Mbp) haplotypes; coalescent-based approximate Bayesian estimation of the time to most recent common ancestor (tMRCA) of the derived allele; forward population simulations to estimate current number of allele carriers; proposal of mutation mechanism; protein structure predictions; co-immunoprecipitation and cycloheximide chase experiments.

Results

Nine European-origin, unrelated c.805_825dup-positive pedigrees (four familial, five sporadic from the UK, USA and France) included 16 affected (nine gigantism/four acromegaly/two non-functioning pituitary adenoma patients and one prospectively diagnosed acromegaly patient) and nine unaffected carriers. All pedigrees shared a 2.79 Mbp haploblock around AIP with additional haploblocks privately shared between subsets of the pedigrees, indicating the existence of an evolutionarily recent common ancestor, the ‘English founder’, with an estimated median tMRCA of 47 generations (corresponding to 1175 years) with a confidence interval (9–113 generations, equivalent to 225–2825 years). The mutation occurred in a small tandem repeat region predisposed to slipped strand mispairing. The resulting seven amino-acid duplication disrupts interaction with HSP90 and leads to a marked reduction in protein stability.

Conclusions

The c.805_825dup allele, originating from a common ancestor, associates with a severe clinical phenotype and a high frequency of gigantism. The mutation is likely to be the result of slipped strand mispairing and affects protein–protein interactions and AIP protein stability.