Thesis (M. Med. Sc.)--University of Hong Kong, 2006.

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2002. / Includes bibliographical references (leaves 137-165). Also available in electronic version. Access restricted to campus users.

published_or_final_version / Zoology / Master / Master of Philosophy

Thesis (M. Phil.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 101-111).

Pheochromocytomas and paragangliomas are neuroendocrine tumors that arise from neural crest-derived cells of the adrenal medulla and the extra-adrenal paraganglia. They cause hypertension due to an abnormally high production of catecholamines (mainly adrenaline and noradrenaline), with symptoms including recurrent episodes of headache, palpitations and sweating, and an increased risk of cardiovascular disease. Malignancy in the form of distant metastases occurs in 10-15% of the patients. The malignant cases are difficult to predict and cure, and have a poor prognosis. About a third of pheochromocytomas and paragangliomas are caused by hereditary mutations in a growing list of known susceptibility genes. However, the cause of the remaining, sporadic, tumors is still largely unknown. The aim of this thesis project has been to further characterize the genetic background of pheochromocytomas and paragangliomas, with a focus on the sporadic tumors. First, we investigated the role of the genes known from the familial tumors in the sporadic form of the disease. By studying mutations, copy number variations, DNA methylation and gene expression, we found that many of the known susceptibility genes harbor somatic alterations in sporadic pheochromocytomas. Particularly, we found that the NF1 gene, which plays an important role in suppressing cell growth and proliferation by regulating the RASMAPK pathway, was inactivated by mutations in more than 20% of the cases. The mutations occurred together with deletions of the normal allele and were associated with a reduced NF1 gene expression and a specific hormone profile. We also detected activating mutations in the gene EPAS1, which encodes HIF-2α, in a subset of sporadic cases. Microarray analysis of gene expression showed that several genes involved in angiogenesis and cell metabolism were upregulated in EPAS1-mutated tumors, which is in agreement with the role of HIF-2α in the cellular response to hypoxia. In order to comprehensively investigate all the known susceptibility genes in a larger patient cohort, we designed a targeted next-generation sequencing approach and could conclude that it was fast and cost-efficient for genetic testing of pheochromocytomas and paragangliomas. The results showed that about 40% of the sporadic cases had mutations in the tested genes. The majority of the mutations were somatic, but some apparently sporadic cases in fact carried germline mutations. Such knowledge of the genetic background can be of importance to facilitate early detection and correct treatment of pheochromocytomas, paragangliomas and potential co-occurring cancers, and also to identify relatives that might be at risk. By sequencing all the coding regions of the genome, the exome, we then identified recurrent activating mutations in a novel gene, in which mutations have previously only been reported in subgroups of brain tumors. The identified mutations are proposed to cause constitutive activation of the encoded receptor tyrosine kinase, resulting in the activation of downstream kinase signaling pathways that promote cell growth and proliferation. In summary, the studies increase our biological understanding of pheochromocytoma and paraganglioma, and possibly also co-occurring cancers in which the same genes and pathways are involved. Together with the findings of other scientific studies, our results may contribute to the development of future treatment options.

In den vergangen Jahren ist durch eine verbesserte Bildgebung die Anzahl der zufällig entdeckten adrenalen Raumforderungen beständig angewachsen. Eine wichtige Differenzialdiagnose sowohl bei adrenalen Inzidentalomen als auch bei der refraktären Hypertonie stellt das Phäochromozytom dar. Aus diesem Hintergrund heraus leitet sich der Wunsch nach Methoden zur sensitiven und spezifischen Bestimmung biochemischer Parameter in der Diagnostik des Phäochromozytoms ab. Derzeit werden hierzu die freien Plasmametanephrine durch High Pressure Liquid Chromatography (HPLC) als Mittel der Wahl angesehen. In der vorliegenden Arbeit wurden bei 113 Patienten mit klinischem Verdacht auf bzw. zum Ausschluss eines Phäochromozytoms die freien Plasmametanephrine mit Hilfe eines Radioimmunoassays (RIA) untersucht. Ziel war zum einen die Evaluierung der freien Metanephrine im Plasma mittels RIA als auch der Vergleich dieser mit anderen biochemischen Parametern und diagnostischen Verfahren hinsichtlich Sensitivität und Spezifität. Der hier verwendete RIA ist relativ zeitnah durchzuführen, kostengünstig und dadurch breit verfügbar. Er zeigt eine hohe diagnostische Sensitivität und Spezifität bei der Bestimmung der freien Metanephrine im Plasma und bietet sich somit für den Einsatz in der Routinediagnostik des Phäochromozytoms an, wodurch verbesserte Aussagen zum Ausschluss bzw. zur Bestätigung der Anwesenheit des Tumors möglich werden.

Catecholamines are stress hormones that are produced and released by a rare tumor called pheochromocytoma. This tumor can cause hypertension which if undiagnosed and untreated leads to death. Since good therapy is available, it is important to find the tumor in time. The most common way to diagnose the tumor is measurement of the biochemical markers; catecholamines and their metabolites, methylated catecholamines. After observation that almost all normetanephrine results for women were higher than the upper reference limit and therefore pathological, the accuracy of the present reference intervals was questioned. Therefore new reference intervals for both urinary catecholamines and methylated catecholamines were developed by analysis of 46 samples using HPLC. Creatinine was analysed in acidified urine in order to see if the results became the same as when analysed in non-acidified urine. Urinary catecholamines and methylated catecholamines were analysed using HPLC. Comparison between measurement of creatinine in acidified urine and non-acidified urine with an enzymatic method was performed using Architect ci 8200, Abbott. As suspected, there was a difference between the present and new intervals. Therefore the new intervals will be used for future diagnosis. There was no difference between the two treatments of creatinine samples wherefore it can be measured in both.In conclusion reference intervals determind in this study will be used and it was shown that creatinine can be measured in acidified urine.

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 3, 2009) Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 128-139).