Genotype-phenotype studies in brain tumors

Abstract: Meningioma and glioma are the most common primary brain tumors, but their etiologies are largely unknown. Although meningioma is usually benign, their intracranial location can lead to lethal consequences, and despite progress in surgery, radiotherapy, and chemotherapy the prognosis for patients with glioma remains poor. The only well-established environmental risk factor for meningioma and glioma is ionizing radiation. Evidence for inherited predisposition to meningioma and glioma is provided by a number of rare inherited syndromes where collectively these diseases account for only a small proportion of the twofold increased risk of brain tumors seen in first-degree relatives for meningioma and glioma patients. It is very possible that much of the excess familial risk is a consequence of co-inheritance of multiple low-risk genetic variations. With this in mind, the aims of the studies in this thesis were to discover genetic risk variants influencing the probability of acquiring the disease and to identify the association between risk variants on the tumor phenotype.To identify genetic variants influencing meningioma risk, a comprehensive tagging of the selected genes in a case-control study was performed. We identified nine risk variants inEGF, ERBB2, and LRIG2 genes. However, these findings could not be confirmed in another larger independent dataset. In addition, the study identified a correlation between LRIG2 protein expression and ER status when analyzed with different parameters. In a separate study with a larger sample of meningioma patients, the same correlation between LRIG2 and ER status was observed.To explore the potential association between reported germline risk variants and somatic genetic events, matched tumor and blood samples from glioma patients were analyzed by SNP array. The results identified correlations betweenEGFR gene variants and somatic aberrations within the EGFR locus and CDKN2A/B locus. To further study the relationship between germline risk variants and tumor phenotype, the same patient material was used and analyzed by three different techniques: SNP array, IHC, and FISH. The results revealed EGFR risk variants effecting copy number variation of the EGFR gene and the expression of the IDH1 and p53. Further comparison between different techniques such as SNP array and FISH analysis revealed the difficulty in achieving consistent results with different techniques.To summarize, the glioma studies show a link between genotype and phenotype where genetic risk variants in theEGFR gene were found to be associated with specific somatic aberrations. These associations are biologically interesting because EGFR is involved in multiple cellular processes. Additional studies of the direct functional role of these observations need to be conducted to elucidate the molecular mechanisms underlying the identified association between germline gene variants and somatic aberrations. For the meningioma studies, no significant risk variants influencing the disease were found but a correlation between LRIG2 and ER status was observed. This result suggests a potential role for the LRIG protein in the pathogenesis of meningioma, but more studies are needed to confirm this hypothesizes.