Genetic epidemiology of glioma

Heritability of nervous system tumors: a sibling-based design

Background

The contribution of genetic and environmental factors to susceptibility to nervous system tumors remains unclear. We performed a quantitative genetic study using a sibling design to estimate the heritability of nervous system tumors, as well as the proportion of the risk of these tumors, which is attributable to environmental factors.

Methods

We conducted a population-based cohort study using Swedish National Register data. All individuals born in Sweden during 1950-2010 with available information on both biological parents were included. A Multi-Generation Register was used to identify family clusters, including both full- and half-siblings. Initially, one index person was randomly selected from each cluster containing only full siblings and one sibling was randomly assigned to this index person. Subsequently, within each of the remaining clusters of full- and half-siblings, an index person was randomly selected, and a half-sibling was randomly assigned to this index person. Among the randomly selected siblings, cases of nervous system tumors were identified using the cancer registry. Quantitative genetic models were used to estimate the proportion of the variance in nervous system tumors attributable to additive genetic factors, shared environment, and individual-specific environment.

Results

The heritability of nervous system tumors was estimated to be 29% (95% confidence interval (CI) = 19%-39%), while the contribution of the non-shared environment to the variance of nervous system tumors was estimated to be 71% (95% CI = 61%-81%). The shared environmental parameter was estimated as zero in the full model.

Conclusion

The variation in susceptibility to nervous system tumors is predominantly attributable to non-shared environmental factors, followed by genetic factors.

Rare germline variants in POLE and POLD1 encoding the catalytic subunits of DNA polymerases ε and δ in glioma families

Pathogenic germline variants in the DNA polymerase genes POLE and POLD1 cause polymerase proofreading-associated polyposis, a dominantly inherited disorder with increased risk of colorectal carcinomas and other tumors. POLE/POLD1 variants may result in high somatic mutation and neoantigen loads that confer susceptibility to immune checkpoint inhibitors (ICIs). To explore the role of POLE/POLD1 germline variants in glioma predisposition, whole-exome sequencing was applied to leukocyte DNA of glioma patients from 61 tumor families with at least one glioma case each. Rare heterozygous POLE/POLD1 missense variants predicted to be deleterious were identified in glioma patients from 10 (16%) families, co-segregating with the tumor phenotype in families with available DNA from several tumor patients. Glioblastoma patients carrying rare POLE variants had a mean overall survival of 21 months. Additionally, germline variants in POLD1, located at 19q13.33, were detected in 2/34 (6%) patients with 1p/19q-codeleted oligodendrogliomas, while POLE variants were identified in 2/4 (50%) glioblastoma patients with a spinal metastasis. In 13/15 (87%) gliomas from patients carrying POLE/POLD1 variants, features of defective polymerase proofreading, e.g. hypermutation, POLE/POLD1-associated mutational signatures, multinucleated cells, and increased intratumoral T cell response, were observed. In a CRISPR/Cas9-derived POLE-deficient LN-229 glioblastoma cell clone, a mutator phenotype and delayed S phase progression were detected compared to wildtype POLE cells. Our data provide evidence that rare POLE/POLD1 germline variants predispose to gliomas that may be susceptible to ICIs. Data compiled here suggest that glioma patients carrying POLE/POLD1 variants may be recognized by cutaneous manifestations, e.g. café-au-lait macules, and benefit from surveillance colonoscopy.

Multi-ancestry genome-wide association study of 4069 children with glioma identifies 9p21.3 risk locus

BACKGROUND

Although recent sequencing studies have revealed that 10% of childhood gliomas are caused by rare germline mutations, the role of common variants is undetermined and no genome-wide significant risk loci for pediatric central nervous system tumors have been identified to date.

METHODS

Meta-analysis of 3 population-based genome-wide association studies comprising 4069 children with glioma and 8778 controls of multiple genetic ancestries. Replication was performed in a separate case-control cohort. Quantitative trait loci analyses and a transcriptome-wide association study were conducted to assess possible links with brain tissue expression across 18 628 genes.

RESULTS

Common variants in CDKN2B-AS1 at 9p21.3 were significantly associated with astrocytoma, the most common subtype of glioma in children (rs573687, P-value of 6.974e-10, OR 1.273, 95% CI 1.179-1.374). The association was driven by low-grade astrocytoma (P-value of 3.815e-9) and exhibited unidirectional effects across all 6 genetic ancestries. For glioma overall, the association approached genome-wide significance (rs3731239, P-value of 5.411e-8), while no significant association was observed for high-grade tumors. Predicted decreased brain tissue expression of CDKN2B was significantly associated with astrocytoma (P-value of 8.090e-8).

CONCLUSIONS

In this population-based genome-wide association study meta-analysis, we identify and replicate 9p21.3 (CDKN2B-AS1) as a risk locus for childhood astrocytoma, thereby establishing the first genome-wide significant evidence of common variant predisposition in pediatric neuro-oncology. We furthermore provide a functional basis for the association by showing a possible link to decreased brain tissue CDKN2B expression and substantiate that genetic susceptibility differs between low- and high-grade astrocytoma.

MR spectroscopy in pediatric neuroradiology

Magnetic resonance spectroscopy (MRS), being able to identify and measure some brain components (metabolites) in pathologic lesions and in normal-appearing tissue, offers a valuable additional diagnostic tool to assess several pediatric neurological diseases. In this review we will illustrate the basic principles and clinical applications of brain proton (H¹; hydrogen) MRS (H¹MRS), by now the only MRS method widely available in clinical practice. Performing H¹MRS in the brain is inherently less complicated than in other tissues (e.g., liver, muscle), in which spectra are heavily affected by magnetic field inhomogeneities, respiration artifacts, and dominating signals from the surrounding adipose tissues. H¹MRS in pediatric neuroradiology has some advantages over acquisitions in adults (lack of motion due to children sedation and lack of brain iron deposition allow optimal results), but it requires a deep knowledge of pediatric pathologies and familiarity with the developmental changes in spectral patterns, particularly occurring in the first two years of life. Examples from our database, obtained mainly from a 1.5 Tesla clinical scanner in a time span of 15 years, will demonstrate the efficacy of H¹MRS in the diagnosis of a wide range of selected pediatric pathologies, like brain tumors, infections, neonatal hypoxic-ischemic encephalopathy, metabolic and white matter disorders.

Multifaceted transforming growth factor-beta (TGFβ) signalling in glioblastoma

Glioblastoma (GBM) is an aggressive and devastating primary brain cancer which responds very poorly to treatment. The average survival time of patients is only 14-15 months from diagnosis so there is a clear and unmet need for the development of novel targeted therapies to improve patient outcomes. The multifunctional cytokine TGFβ plays fundamental roles in development, adult tissue homeostasis, tissue wound repair and immune responses. Dysfunction of TGFβ signalling has been implicated in both the development and progression of many tumour types including GBM, thereby potentially providing an actionable target for its treatment. This review will examine TGFβ signalling mechanisms and their role in the development and progression of GBM. The targeting of TGFβ signalling using a variety of approaches including the TGFβ binding protein Decorin will be highlighted as attractive therapeutic strategies.

Dissecting Molecular Features of Gliomas: Genetic Loci and Validated Biomarkers

Recently, several studies focused on the genetics of gliomas. This allowed identifying several germline loci that contribute to individual risk for tumor development, as well as various somatic mutations that are key for disease classification. Unfortunately, none of the germline loci clearly confers increased risk per se. Contrariwise, somatic mutations identified within the glioma tissue define tumor genotype, thus representing valid diagnostic and prognostic markers. Thus, genetic features can be used in glioma classification and guided therapy. Such copious genomic variabilities are screened routinely in glioma diagnosis. In detail, Sanger sequencing or pyrosequencing, fluorescence in-situ hybridization, and microsatellite analyses were added to immunohistochemistry as diagnostic markers. Recently, Next Generation Sequencing was set-up as an all-in-one diagnostic tool aimed at detecting both DNA copy number variations and mutations in gliomas. This approach is widely used also to detect circulating tumor DNA within cerebrospinal fluid from patients affected by primary brain tumors. Such an approach is providing an alternative cost-effective strategy to genotype all gliomas, which allows avoiding surgical tissue collection and repeated tumor biopsies. This review summarizes available molecular features that represent solid tools for the genetic diagnosis of gliomas at present or in the next future.

MicroRNA-181 inhibits the proliferation, drug sensitivity and invasion of human glioma cells by targeting Selenoprotein K (SELK)

Gliomas are aggressive type of brain tumors and cause significant human mortality world over. The frequent relapses, development of drug resistance, the adverse effects of the chemotherapy and dearth of the therapeutic targets form the major hurdles in glioma treatment. Several studies suggest that microRNAs (miRs) are involved in the development and progression of different cancers. Herein, the therapeutic potential of miR-181 was explored in human glioma cells. The results showed that miR-181 is significantly downregulated in human glioma cells. Overexpression of miR-181 caused significant inhibition in the proliferation of U87 and U118 glioma cells. The miR-181 triggered growth inhibition was found to be mainly due to the induction of apoptosis which was concomitant with increase in the Bax/Bcl-2 ratio. Additionally, miR-181 enhanced the chemosensitivity of the glioma cells to temozolomide and suppressed their invasion. Bioinformatic analysis showed that miR-181 exerts its effects by inhibiting the expression of Selenoprotein K (SELK). The expression of SELK was found to be significantly upregulated in glioma cells and silencing of SELK suppressed the proliferation of glioma cells. Nonetheless, overexpression of SELK could nullify the effects of miR-181 on the proliferation of the glioma cells. Taken together, miR-181 may exhibit therapeutic implications in the treatment of glioma.

Genetic and molecular epidemiology of adult diffuse glioma

The WHO 2007 glioma classification system (based primarily on tumour histology) resulted in considerable interobserver variability and substantial variation in patient survival within grades. Furthermore, few risk factors for glioma were known. Discoveries over the past decade have deepened our understanding of the molecular alterations underlying glioma and have led to the identification of numerous genetic risk factors. The advances in molecular characterization of glioma have reframed our understanding of its biology and led to the development of a new classification system for glioma. The WHO 2016 classification system comprises five glioma subtypes, categorized by both tumour morphology and molecular genetic information, which led to reduced misclassification and improved consistency of outcomes within glioma subtypes. To date, 25 risk loci for glioma have been identified and several rare inherited mutations that might cause glioma in some families have been discovered. This Review focuses on the two dominant trends in glioma science: the characterization of diagnostic and prognostic tumour markers and the identification of genetic and other risk factors. An overview of the many challenges still facing glioma researchers is also included.

MDM4 contributes to the increased risk of glioma susceptibility in Han Chinese population

Recently, MDM4 gene has been reported to be a susceptibility gene for glioma in Europeans, but the molecular mechanism of glioma pathogenesis remains unknown. The aim of this study was to investigate whether common variants of MDM4 contribute to the risk of glioma in Han Chinese individuals. A total of 24 single-nucleotide polymorphisms (SNPs) of the MDM4 gene were assessed in a dataset of 562 glioma patients (non-glioblastoma) and 1,192 cancer-free controls. The SNP rs4252707 was found to be strongly associated with the risk of non-GBM (P = 0.000101, adjusted odds ratio (OR) = 1.34, 95% confidence interval (CI) = 1.16–1.55). Further analyses indicated that there was a significant association between A allele of rs4252707 associated with the increased non-GBM risk. Haplotype analysis also confirmed a result similar to that of the single-SNP analysis. Using stratification analyses, we found the association of rs4252707 with an increased non-GBM risk in adults (≥18 years, P = 0.0016) and individuals without IR exposure history (P = 0.0013). Our results provide strong evidence that the MDM4 gene is tightly linked to genetic susceptibility for non-GBM risk in Han Chinese population, indicating a important role for MDM4 gene in the etiology of glioma.

Molecular subtyping of tumors from patients with familial glioma

Background

Single-gene mutation syndromes account for some familial glioma (FG); however, they make up only a small fraction of glioma families. Gliomas can be classified into 3 major molecular subtypes based on isocitrate dehydrogenase (IDH) mutation and 1p/19q codeletion. We hypothesized that the prevalence of molecular subtypes might differ in familial versus sporadic gliomas and that tumors in the same family should have the same molecular subtype.

Methods

Participants in the FG study (Gliogene) provided samples for germline DNA analysis. Formalin-fixed, paraffin-embedded tumors were obtained from a subset of FG cases, and DNA was extracted. We analyzed tissue from 75 families, including 10 families containing a second affected family member. Copy number variation data were obtained using a first-generation Affymetrix molecular inversion probe (MIP) array.

Results

Samples from 62 of 75 (83%) FG cases could be classified into the 3 subtypes. The prevalence of the molecular subtypes was: 30 (48%) IDH-wildtype, 21 (34%) IDH-mutant non-codeleted, and 11 (19%) IDH-mutant and 1p/19q codeleted. This distribution of molecular subtypes was not statistically different from that of sporadic gliomas (P = 0.54). Of 10 paired FG samples, molecular subtypes were concordant for 7 (κ = 0.59): 3 IDH-mutant non-codeleted, 2 IDH-wildtype, and 2 IDH-mutant and 1p/19q codeleted gliomas.

Conclusions

Our data suggest that within individual families, patients develop gliomas of the same molecular subtype. However, we did not observe differences in the prevalence of the molecular subtypes in FG compared with sporadic gliomas. These observations provide further insight into the distribution of molecular subtypes in FG.

Epidemiology of Brain Tumors

Brain tumors are the commonest solid tumor in children, leading to significant cancer-related mortality. Several hereditary syndromes associated with brain tumors are nonfamilial. Ionizing radiation is a well-recognized risk factor for brain tumors. Several industrial exposures have been evaluated for a causal association with brain tumor formation but the results are inconclusive. A casual association between the common mutagens of tobacco, alcohol, or dietary factors has not yet been established. There is no clear evidence that the incidence of brain tumors has changed over time. This article presents the descriptive epidemiology of the commonest brain tumors of children and adults.

New insights into the genetics of glioblastoma multiforme by familial exome sequencing

Glioblastoma multiforme (GBM) is the most aggressive and malignant subtype of human brain tumors. While a family clustering of GBM has long been acknowledged, relevant hereditary factors still remained elusive. Exome sequencing of families offers the option to discover respective genetic factors.We sequenced blood samples of one of the rare affected families: while both parents were healthy, both children were diagnosed with GBM. We report 85 homozygous non-synonymous single nucleotide variations (SNVs) in both siblings that were heterozygous in the parents. Beyond known key players for GBM such as ERBB2, PMS2, or CHI3L1, we identified over 50 genes that have not been associated to GBM so far. We also discovered three accumulative effects potentially adding to the tumorigenesis in the siblings: a clustering of multiple variants in single genes (e.g., PTPRB, CROCC), the aggregation of affected genes on specific molecular pathways (e.g., Focal adhesion or ECM receptor interaction) and genomic proximity (e.g., chr22.q12.2, chr1.p36.33). We found a striking accumulation of SNVs in specific genes for the daughter, who developed not only a GBM at the age of 12 years but was subsequently diagnosed with a pilocytic astrocytoma, a common acute lymphatic leukemia and a diffuse pontine glioma.The reported variants underline the relevance of genetic predisposition and cancer development in this family and demonstrate that GBM has a complex and heterogeneous genetic background. Sequencing of other affected families will help to further narrow down the driving genetic causes for this disease.

Genetic counseling and tumor predisposition in neuro-oncology practice

Tumor predisposition syndromes may be under-recognized in neuro-oncology practice. Identifying patients with a hereditary tumor predisposition permits appropriate tumor management as well as surveillance and risk-reduction measures for patients and their families. The American College of Medical Genetics and Genomics and the National Society of Genetic Counselors recently published referral guidelines for tumor predisposition assessment, providing an impetus to review the use of genetic counseling in neuro-oncology and to describe features of the less stereotypic conditions from the perspective of neuro-oncology practice. This review also provides a framework for the identification and management of these conditions, as well as references to guidelines and resources for providers and patients.

Recent developments in brain tumor predisposing syndromes

The etiologies of brain tumors are in the most cases unknown, but improvements in genetics and DNA screening have helped to identify a wide range of brain tumor predisposition disorders. In this review we are discussing some of the most common predisposition disorders, namely: neurofibromatosis type 1 and 2, schwannomatosis, rhabdoid tumor predisposition disorder, nevoid basal cell carcinoma syndrome (Gorlin), tuberous sclerosis complex, von Hippel-Lindau, Li-Fraumeni and Turcot syndromes. Recent findings from the GLIOGENE collaboration and the newly identified glioma causing gene POT1, will also be discussed. Genetics. We will describe these disorders from a genetic and clinical standpoint, focusing on the difference in clinical symptoms depending on the underlying gene or germline mutation. Central nervous system (CNS) tumors. Most of these disorders predispose the carriers to a wide range of symptoms. Herein, we will focus particularly on tumors affecting the CNS and discuss improvements of targeted therapy for the particular disorders.

Quantifying the heritability of glioma using genome-wide complex trait analysis

Genome-wide association studies (GWAS) have successfully identified a number of common single-nucleotide polymorphisms (SNPs) influencing glioma risk. While these SNPs only explain a small proportion of the genetic risk it is unclear how much is left to be detected by other, yet to be identified, common SNPs. Therefore, we applied Genome-Wide Complex Trait Analysis (GCTA) to three GWAS datasets totalling 3,373 cases and 4,571 controls and performed a meta-analysis to estimate the heritability of glioma. Our results identify heritability estimates of 25% (95% CI: 20-31%, P = 1.15 × 10(-17)) for all forms of glioma - 26% (95% CI: 17-35%, P = 1.05 × 10(-8)) for glioblastoma multiforme (GBM) and 25% (95% CI: 17-32%, P = 1.26 × 10(-10)) for non-GBM tumors. This is a substantial increase from the genetic variance identified by the currently identified GWAS risk loci (~6% of common heritability), indicating that most of the heritable risk attributable to common genetic variants remains to be identified.

Perinatal and familial risk factors for brain tumors in childhood through young adulthood

Perinatal factors, including high birth weight, have been associated with childhood brain tumors in case-control studies. However, the specific contributions of gestational age and fetal growth remain unknown, and these issues have never been examined in large cohort studies with follow-up into adulthood. We conducted a national cohort study of 3,571,574 persons born in Sweden in 1973-2008, followed up for brain tumor incidence through 2010 (maximum age 38 years) to examine perinatal and familial risk factors. There were 2,809 brain tumors in 69.7 million person-years of follow-up. After adjusting for potential confounders, significant risk factors for brain tumors included high fetal growth [incidence rate ratio (IRR) per additional 1 SD, 1.04; 95% confidence interval (CI), 1.01-1.08, P = 0.02], first-degree family history of a brain tumor (IRR, 2.43; 95% CI, 1.86-3.18, P < 0.001), parental country of birth (IRR for both parents born in Sweden vs. other countries, 1.21; 95% CI, 1.09-1.35, P < 0.001), and high maternal education level (Ptrend = 0.01). These risk factors did not vary by age at diagnosis. The association with high fetal growth appeared to involve pilocytic astrocytomas, but not other astrocytomas, medulloblastomas, or ependymomas. Gestational age at birth, birth order, multiple birth, and parental age were not associated with brain tumors. In this large cohort study, high fetal growth was associated with an increased risk of brain tumors (particularly pilocytic astrocytomas) independently of gestational age, not only in childhood but also into young adulthood, suggesting that growth factor pathways may play an important long-term role in the etiology of certain brain tumor subtypes.

DNA repair gene XRCC3 Thr241Met polymorphism and glioma risk: a meta-analysis

BACKGROUND

The polymorphism of XRCC3 Thr241Met has been indicated to be correlated with glioma susceptibility, but study results are still debatable. The present meta-analysis was performed to investigate the association between XRCC3 Thr241Met polymorphism and glioma.

METHODS

A total of 3754 glioma patients and 4849 controls from nine separate studies were involved. The pooled odds ratio (OR) and its corresponding 95% confidence interval (CI) was assessed by the random-effects model.

RESULTS

The association between XRCC3 Thr241Met polymorphism and glioma was significant in the recessive model (OR = 1.36; 95% CI, 1.02 - 1.82; P = 0.03). In a stratified analysis by the ethnicity, significantly increased risk was detected in Asians (OR = 1.93; 95% CI, 1.18 - 3.17; P = 0.009).

CONCLUSIONS

In conclusion, XRCC3 Thr241Met polymorphism was implied to be associated with increased glioma risk. More studies are needed to validate this result.

Known glioma risk loci are associated with glioma with a family history of brain tumours -- a case-control gene association study

Familial cancer can be used to leverage genetic association studies. Recent genome-wide association studies have reported independent associations between seven single nucleotide polymorphisms (SNPs) and risk of glioma. The aim of this study was to investigate whether glioma cases with a positive family history of brain tumours, defined as having at least one first- or second-degree relative with a history of brain tumour, are associated with known glioma risk loci. One thousand four hundred and thirty-one glioma cases and 2,868 cancer-free controls were identified from four case-control studies and two prospective cohorts from USA, Sweden and Denmark and genotyped for seven SNPs previously reported to be associated with glioma risk in case-control designed studies. Odds ratios were calculated by unconditional logistic regression. In analyses including glioma cases with a family history of brain tumours (n = 104) and control subjects free of glioma at baseline, three of seven SNPs were associated with glioma risk: rs2736100 (5p15.33, TERT), rs4977756 (9p21.3, CDKN2A-CDKN2B) and rs6010620 (20q13.33, RTEL1). After Bonferroni correction for multiple comparisons, only one marker was statistically significantly associated with glioma risk, rs6010620 (ORtrend for the minor (A) allele, 0.39; 95% CI: 0.25-0.61; Bonferroni adjusted ptrend , 1.7 × 10(-4) ). In conclusion, as previously shown for glioma regardless of family history of brain tumours, rs6010620 (RTEL1) was associated with an increased risk of glioma when restricting to cases with family history of brain tumours. These findings require confirmation in further studies with a larger number of glioma cases with a family history of brain tumours.

Description of selected characteristics of familial glioma patients - results from the Gliogene Consortium

BACKGROUND

While certain inherited syndromes (e.g. Neurofibromatosis or Li-Fraumeni) are associated with an increased risk of glioma, most familial gliomas are non-syndromic. This study describes the demographic and clinical characteristics of the largest series of non-syndromic glioma families ascertained from 14 centres in the United States (US), Europe and Israel as part of the Gliogene Consortium.

METHODS

Families with 2 or more verified gliomas were recruited between January 2007 and February 2011. Distributions of demographic characteristics and clinical variables of gliomas in the families were described based on information derived from personal questionnaires.

FINDINGS

The study population comprised 841 glioma patients identified in 376 families (9797 individuals). There were more cases of glioma among males, with a male to female ratio of 1.25. In most families (83%), 2 gliomas were reported, with 3 and 4 gliomas in 13% and 3% of the families, respectively. For families with 2 gliomas, 57% were among 1st-degree relatives, and 31.5% among 2nd-degree relatives. Overall, the mean (±standard deviation [SD]) diagnosis age was 49.4 (±18.7) years. In 48% of families with 2 gliomas, at least one was diagnosed at <40y, and in 12% both were diagnosed under 40y of age. Most of these families (76%) had at least one grade IV glioblastoma multiforme (GBM), and in 32% both cases were grade IV gliomas. The most common glioma subtype was GBM (55%), followed by anaplastic astrocytoma (10%) and oligodendroglioma (8%). Individuals with grades I-II were on average 17y younger than those with grades III-IV.

INTERPRETATION

Familial glioma cases are similar to sporadic cases in terms of gender distribution, age, morphology and grade. Most familial gliomas appear to comprise clusters of two cases suggesting low penetrance, and that the risk of developing additional gliomas is probably low. These results should be useful in the counselling and clinical management of individuals with a family history of glioma.

Genetics of adult glioma

Gliomas make up approximately 30% of all brain and central nervous system tumors and 80% of all malignant brain tumors. Despite the frequency of gliomas, the etiology of these tumors remains largely unknown. Diffuse gliomas, including astrocytomas and oligodendrogliomas, belong to a single pathologic class but have very different histologies and molecular etiologies. Recent genomic studies have identified separate molecular subtypes within the glioma classification that appear to correlate with biological etiology, prognosis, and response to therapy. The discovery of these subtypes suggests that molecular genetic tests are and will be useful, beyond classical histology, for the clinical classification of gliomas. While a familial susceptibility to glioma has been identified, only a small percentage of gliomas are thought to be due to single-gene hereditary cancer syndromes. Through the use of linkage studies and genome-wide association studies, multiple germline variants have been identified that are beginning to define the genetic susceptibility to glioma.

Familial glioblastoma: A case report of glioblastoma in two brothers and review of literature

Background:

Gliomas that aggregate in families with history of malignancy may have an inheritable genetic basis. Gliomas can occur in several well known tumor syndromes. However, their occurrence in the absence of these syndromes is quite rare. High-grade gliomas, such as glioblastoma multiforme (GBM), are the most common and most lethal primary cancers of the central nervous system (CNS).

Case Description:

We present a case of two brothers both diagnosed with GBM. Both siblings underwent biopsy with debulking of the tumors by different surgeons. Only one sibling elected to undergo chemotherapy and radiation. Cytogenetic studies were possible only on one sibling and the tumor specimen revealed multiple chromosomal abnormalities, including triploidies 4, 8, 12, 22 and loss of heterozygosity of 1p, 9p, and 10. Histological samples for both tumors were similar, both revealing increased cellularity consisting of gemistocytic astrocytes, central necrosis, and microvascularization.

Conclusion:

We present two brothers who display a rare familial relationship in the development of their GBMs. Supplementary and improved genetic studies may allow for specific treatment modalities as certain genetic abnormalities have better response to tailored treatments and carry better prognoses.

Detailed characterization of alterations of chromosomes 7, 9, and 10 in glioblastomas as assessed by single-nucleotide polymorphism arrays

Glioblastomas are cytogenetically heterogeneous tumors that frequently display alterations of chromosomes 7, 9p, and 10q. We used high-density (500K) single-nucleotide polymorphism arrays to investigate genome-wide copy number alterations and loss of heterozygosity in 35 primary glioblastomas. We focused on the identification and detailed characterization of alterations involving the most frequently altered chromosomes (chromosomes 7, 9, and 10), the identification of distinct prognostic subgroups of glioblastomas based on the cytogenetic patterns of alteration for these chromosomes, and validation of their prognostic impact in a larger series of tumors from public databases. Gains of chromosome 7 (97%), with or without epidermal growth factor receptor (EGFR) amplification, and losses of chromosomes 9p (83%) and 10 (91%) were the most frequent alterations. Such alterations defined five different cytogenetic groups with a significant effect on patient survival; notably, EGFR amplification (29%) was associated with a better survival among older patients, as confirmed by multivariate analysis of a larger series of glioblastomas from the literature. In addition, our results provide further evidence about the relevance of other genes (eg, EGFR, CDKN2A/B, MTAP) in the pathogenesis of glioblastomas. Altogether, our results confirm the cytogenetic heterogeneity of glioblastomas and suggest that their stratification based on combined assessment of cytogenetic alterations involving chromosomes 7, 9, and 10 may contribute to the prognostic evaluation of glioblastomas.

Pesticides and brain cancer linked in orchard farmers of Kashmir

Background:

The atmosphere of valley of Kashmir is ideal for fresh and dry fruit production. Millions of tons of pesticides, insecticides and fungicides (chemicals like chlorpyriphos, mancozeb, captan, dimethoate, phosalone, etc.) are being used by the orchard farmers to spray the plants, fruits and the leaves every year. The increasing trend in the incidence of primary malignant brain tumors in orchard farmers of Kashmir is alarming.

Aim:

To determine the relationship between the patients of primary malignant brain tumors and their occupation.

Materials and Methods:

Retrospectively case files along with death certificates of 432 patients of primary malignant brain tumors and 457 controls (non-tumor neurologic diseases), admitted for treatment simultaneously over a period of 4 years from January 2005 to December 2008, to the Department of Neurosurgery, Sher-I-Kashmir Institute of Medical Sciences (SKIMS), Kashmir, were studied. Follow-up and family contact was established. The serum cholinesterase activity was measured by kinetic/DGKC calorimetric method and ethylenediaminetetraacetic acid (EDTA) samples were sent to the laboratory. The results are expressed in U/l which is U/l×1000. The laboratory at SKIMS, Srinagar, and Dr Lal PathLabs at New Delhi used a reference range for serum cholinesterase as 3167–6333 U/l.

Results:

Analysis revealed that 90.04% (389 out of 432) patients were orchard-farm workers, orchard residents and orchard playing children exposed to the high levels of multiple types of neurotoxic and carcinogenic (chlorpyriphos, dimethoate, mancozeb and captan) chemicals for more than 10–20 years. About 31.9% (124 out of 389) of these from both sexes were younger than 40 years beginning exposure at an early age and had higher (<6334 U/l) serum cholinesterase (SCE) levels. The 9.96% (43 out of 432) patients were not exposed to pesticides. On the other hand, only 119 patients out of 457 controls had recorded history of pesticide exposure and 338 were unrelated to pesticides. Out of 389 patients, 71.7% (279 out of 389) were males and 28.3% (110 out of 389) including 7 members of three families, 6 were females and 1 male.

Conclusion:

All orchard-related 389 patients had high grade tumors as compared to the non-pesticide tumors. Mortality in pesticide exposed tumors was 12%. Higher levels of SCE were found in 31.9% (124 out of 389) patients and decreased levels in only 45.3% (176 out of 389) orchard-related patients. The significantcase/control odds ratio (OR) of 0.28, hospital control SCE OR of 1.1 and family control SCE OR of 1.5, points the finger of suspicion toward the link between pesticides and brain cancer.

Brain cancer and pesticide relationship in orchard farmers of Kashmir

Background:

The increasing trend in the incidence of primary malignant brain tumors in orchard farmers and their families in Kashmir.

Aim:

To determine the relationship between the patients of primary malignant brain tumors and their occupation.

Materials and Methods:

Retrospectively, case files along with death certificates of 432 patients of primary malignant brain tumors and 457 controls (non-tumor neurologic diseases), admitted for treatment simultaneously over a period of 4 years from January 2005 to December 2008, to the Neurosurgery, Sher-i-Kashmir Institute of Medical Sciences (SKIMS), Kashmir, were studied. Follow-up and family interaction was established.

Results:

Analysis revealed that 90.04% (389 out of 432) patients were orchard farm workers, orchard residents and orchard playing children exposed to the high levels of multiple types of neurotoxic and carcinogenic (chlorpyriphos, dimethoate, mancozeb and captan) chemicals for more than 10 years [relative risk (RR) = 10.6; odds ratio (OR) = >10; 95% confidence interval (CI) = >25-40]. The 9.96% (43 out of 432) patients were not exposed to pesticides. On the other hand, only 19 patients out of 457 controls had recorded history of pesticide exposure and 438 were unrelated to pesticides. Out of 389 patients, 71.7% (279 out of 389) were males and 28.3% (110 out of 389), including six members of three families, were females (one male child).

Conclusion:

All orchard-related 389 patients had high-grade tumors as compared to the non-pesticide tumors. Mortality in pesticide-exposed tumors was 12%. The higher or upper-normal levels of serum cholinesterase (AChE) were observed in 54.7% (213 out of 389) patients and decreased levels were found in only 45.3% (176 out of 389) orchard-related patients (RR = 19.4; OR = >5; 95% CI = >1-10). Although serum AChE levels were a routine investigation in malignant brain tumors, this was not a routine in other neurological conditions (hospitalized controls). The familial gliomas have shown an emerging trend in the orchard residents of valley of Kashmir.

A comprehensive study of the association between the EGFR and ERBB2 genes and glioma risk

Glioma is the most common type of adult brain tumor and glioblastoma, its most aggressive form, has a dismal prognosis. Receptor tyrosine kinases such as the epidermal growth factor receptor (EGFR, ERBB2, ERBB3, ERBB4) family, and the vascular endothelial growth factor receptor (VEGFR), play a central role in tumor progression. We investigated the genetic variants of EGFR, ERBB2, VEGFR and their ligands, EGF and VEGF on glioma and glioblastoma risk. In addition, we evaluated the association of genetic variants of a newly discovered family of genes known to interact with EGFR: LRIG2 and LRIG3 with glioma and glioblastoma risk. Methods. We analyzed 191 tag single nucleotide polymorphisms (SNPs) capturing all common genetic variation of EGF, EGFR, ERBB2, LRIG2, LRIG3, VEGF and VEGFR2 genes. Material from four case-control studies with 725 glioma patients (329 of who were glioblastoma patients) and their 1 610 controls was used. Haplotype analyses were conducted using SAS/Genetics software. Results. Fourteen of the SNPs were significantly associated with glioma risk at p< 0.05, and 17 of the SNPs were significantly associated with glioblastoma risk at p< 0.05. In addition, we found that one EGFR haplotype was related to increased glioblastoma risk at p=0.009, Odds Ratio [OR] = 1.67 (95% confidence interval (CI): 1.14, 2.45). The Bonferroni correction made all p-values non-significant. One SNP, rs4947986 next to the intron/exon boundary of exon 7 in EGFR, was validated in an independent data set of 713 glioblastoma and 2 236 controls, [OR] = 1.42 (95% CI: 1.06,1.91). Discussion. Previous studies show that regulation of the EGFR pathway plays a role in glioma progression but the present study is the first to find that certain genotypes of the EGFR gene may be related to glioblastoma risk. Further studies are required to reinvestigate these findings and evaluate the functional significance.

Familial risks in nervous system tumours: joint Nordic study

Background:

Familial nervous system cancers are rare and limited data on familial aspects are available particularly on site-specific tumours.

Methods:

Data from five Nordic countries were used to analyse familial risks of nervous system tumours. Standardised incidence ratios (SIRs) were calculated for offspring of affected relatives compared with offspring of non-affected relatives.

Results:

The total number of patients with nervous system tumour was 63 307, of whom 32 347 belonged to the offspring generation. Of 851 familial patients (2.6%) in the offspring generation, 42 (4.7%) belonged to the families of a parent and at least two siblings affected. The SIR of brain tumours was 1.7 in offspring of affected parents; it was 2.0 in siblings and 9.4 in families with a parent and sibling affected. For spinal tumours, the SIRs were much higher for offspring of early onset tumours, 14.0 for offspring of affected parents and 22.7 for siblings. The SIRs for peripheral nerve tumours were 16.3 in offspring of affected parents, 27.7 in siblings and 943.9 in multiplex families.

Conclusion:

The results of this population-based study on medically diagnosed tumours show site-, proband- and age-specific risks for familial tumours, with implications for clinical genetic counselling and identification of the underlying genes.

Hereditary tumor syndromes and gliomas

Several congenital syndromes caused by germline mutations in tumor suppressor genes predispose to the development of glial tumors. In the last few decades our knowledge about the molecular functions of these genes and the pathogenesis of hereditary tumor syndromes has greatly increased. The most common syndromes are the neurofibromatoses (type 1 and type 2) and the tuberous scleroses complex. There are interesting overlaps in the molecular pathogen-esis. Deregulation of Ras or downstream Ras pathways including MEK/ERK and AKT/ mTOR plays an important role in these three syndromes. Other rare syndromes include Li-Fraumeni, melanoma-astrocytoma, and Turcot syndrome involving cell cycle regulators and DNA repair genes. The genes and pathways involved in the pathogenesis of these syndromes also play an important role in the development of sporadic tumors. Therefore research on hereditary syndromes contributes substantially to our understanding of tumor formation.

[Epidemiology of primary brain tumor]

Two main approaches are generally used to study the epidemiology of primary brain tumors. The first approach is to identify risk factors, which may be intrinsic or related to external causes. The second main approach is descriptive. Intrinsic factors potentially affecting risk include genetic predisposition and susceptibility, gender, race, birth weight and allergy. Radiation exposure is the main extrinsic factor affecting risk. A large body of work devoted, among others, to electromagnetic fields and especially cellular phones, substitutive hormonal therapy, pesticides, and diet have been published. To date, results have been discordant. Descriptive epidemiological studies have reported an increasing annual incidence of primary brain tumors in industrialized countries. The main reasons are the increasing age of the population and better access to diagnostic imaging. Comparing incidences from one registry to another is difficult. Spatial and temporal variations constitute one explanation and evolutions in coding methods another. In all registries, weak incidence of primary brain tumors constitute a very important limiting factor. Renewed interest from the neuro-oncological community is needed to obtain pertinent and essential data which could facilitate improved knowledge on this topic.

Familial risks in nervous-system tumours: a histology-specific analysis from Sweden and Norway

BACKGROUND

There are limited data available on tumour subtype-specific familial risks for nervous-system tumours. We aimed to provide such data at the population level.

METHODS

We used data from the nationwide Swedish and Norwegian databases on familial cancer to calculate standardised incidence ratios (SIRs) for the familial risk of developing a nervous-system tumour in offspring born after 1931 (Sweden) or 1900 (Norway) whose parents or siblings were probands.

FINDINGS

54 195 patients had nervous-system tumours, 22 331 of whom belonged to the offspring generation aged 0-72 years in Sweden and 0-51 years in Norway. Of 709 familial patients in the offspring generation, 438 (61.8%) had a parent affected by a nervous-system tumour (SIR 1.66; 95% CI 1.51-1.82), 236 (33.3%) had a sibling affected by a nervous-system tumour (SIR 2.01; 95% CI 1.76-2.28), and 35 (4.9%) belonged to families with a parent and at least two siblings affected by a nervous-system tumour (multiplex families; SIR 13.40; 95% CI 9.33-18.66). The SIR for glioma was 1.8 (1.5-2.0) when a parent was a proband, but increased to 11.2 (5.7-19.5) in multiplex families. Early-onset neurinoma and haemangioma showed high familial risks; with an SIR for neurinoma of 1.7 (1.4-2.2) for offspring of affected parents, 2.7 (2.0-3.5) for siblings, and 27.2 (13.5-48.8) for multiplex families, and an SIR for haemangioma of 2.4 (1.4-3.8) for offspring of affected parents. Histology-specific population-based familial risks were shown for meningioma (1.6 for offspring of affected parents; 95% CI 1.3-2.0), ependymoma (2.7 for young offspring <20 years; 1.1-5.5), medulloblastoma (4.1 for siblings; 1.7-8.1), and neuroblastoma (3.2 for siblings; 1.1-6.9).

INTERPRETATION

Our results suggest a complex genetic background for nervous-system tumours, which differs depending on the age of onset and histological subtype of the tumour. High sibling risks might suggest recessive inheritance. As the high-penetrant multiplex families only accounted for about 5% of familial nervous-system tumours, most familial cases are probably caused by low-penetrance genes.

FUNDING

The Nordic Cancer Union, Deutsche Krebshilfe, the Swedish Cancer Society, and the Swedish Council for Working Life and Social Research.

Epidemiology of brain tumors

Gliomas account for more than 70% of all brain tumors, and of these, glioblastoma is the most frequent and malignant histologic type (World Health Organization [WHO] grade IV). There is a tendency toward a higher incidence of gliomas in highly developed, industrialized countries. Some reports indicate that Caucasians have a higher incidence than African or Asian populations. With the exception of pilocytic astrocytomas (WHO grade I), the prognosis of glioma patients is still poor. Fewer than 3% of glioblastoma patients are still alive at 5 years after diagnosis, older age being the most significant and consistent prognostic factor of poorer outcome. Gliomas are components of several inherited tumor syndromes, but the prevalence of these syndromes is very low. Many environmental and lifestyle factors including several occupations, environmental carcinogens, and diet have been reported to be associated with an elevated glioma risk, but the only factor unequivocally associated with an increased risk is therapeutic X-irradiation. In particular, children treated with X-irradiation for acute lymphoblastic leukemia show a significantly elevated risk of developing gliomas and primitive neuroectodermal tumors, often within 10 years after therapy. Significant correlation between G:C --> A:T transitions in the TP53 gene and promoter methylation of the O6 -methylguanine-DNA methyltransferase (MGMT) gene in glio-mas have been reported in several studies, suggesting the possible involvement of O6-methylguanine DNA adducts, which may be produced by exogenous or endogenous alkylating agents in the development of gliomas.

Brain tumor susceptibility: the role of genetic factors and uses of mouse models to unravel risk

Brain tumors are relatively rare but deadly cancers, and present challenges in the determination of risk factors in the population. These tumors are inherently difficult to cure because of their protected location in the brain, with surgery, radiation and chemotherapy options carrying potentially lasting morbidity for patients and incomplete cure of the tumor. The development of methods to prevent or detect brain tumors at an early stage is extremely important to reduce damage to the brain from the tumor and the therapy. Developing effective prevention or early detection methods requires a deep understanding of the risk factors for brain tumors. This review explores the difficulties in assessing risk factors in rare diseases such as brain tumors, and discusses how mouse models of cancer can aid in a better understanding of genetic risk factors for brain tumors.

Familiality in brain tumors

BACKGROUND

Familiality in brain tumors is not definitively substantiated.

METHODS

We used the Utah Population Data Base (UPDB), a genealogy representing the Utah pioneers and their descendants, record-linked to statewide cancer records, to describe the familial nature of primary brain cancer. We examined the familial clustering of primary brain tumors, including subgroups defined by histologic type and age at diagnosis. The UPDB includes 1,401 primary brain tumor cases defined as astrocytoma or glioblastoma, all with at least three generations of genealogy data. We tested the hypothesis of excess relatedness of brain tumor cases using the Genealogical Index of Familiality method. We estimated relative risks for brain tumors in relatives using rates of brain tumors estimated internally.

RESULTS

Significant excess relatedness was observed for astrocytomas and glioblastomas considered as a group (n = 1,401), for astrocytomas considered separately (n = 744), but not for glioblastomas considered separately (n = 658). Significantly increased risks to first- and second-degree relatives for astrocytomas were identified for relatives of astrocytomas considered separately. Significantly increased risks to first-degree relatives, but not second degree, were observed for astrocytoma and glioblastoma cases considered together, and for glioblastoma cases considered separately.

CONCLUSIONS

This study provides strong evidence for a familial contribution to primary brain cancer risk. There is evidence that this familial aspect includes not only shared environment, but also a heritable component. Extended high-risk brain tumor pedigrees identified in the UPDB may provide the opportunity to identify predisposition genes responsible for familial brain tumors.

An international case-control study of interleukin-4Ralpha, interleukin-13, and cyclooxygenase-2 polymorphisms and glioblastoma risk

Previous studies found that allergies are inversely related to risk of glioma. In an earlier publication, using data from a Swedish case-control study, Schwartzbaum et al. report an inverse relation between risk of glioblastoma and four single nucleotide polymorphisms (SNP) on two genes [interleukin (IL)-4Ralpha, IL-13] that are associated with allergies. In addition, recent studies suggest that IL-4 and IL-13 induce cyclooxygenase-2 (COX-2) to resolve brain inflammation. To see whether previous Swedish results (110 cases, 430 controls) would be replicated, we estimated the association between glioblastoma and two IL-4Ralpha (rs1805015, rs1801275) and two IL-13 (rs20541, rs1800925) SNPs and their haplotypes and one COX-2 SNP (-765GC) using additional English, Danish, and Finnish data (217 cases, 1,171 controls). Among general population controls, we evaluated associations between these haplotypes, the COX-2 SNP, and self-reported allergies. Our data did not support our original observations relating individual IL-4Ralpha, IL-13, or COX-2 SNPs to glioblastoma risk. However, the T-G IL-4Ralpha haplotype was associated with glioblastoma risk (odds ratio, 2.26; 95% confidence interval, 1.13-4.52) and there was a suggestion of an inverse relation between this haplotype and hayfever prevalence among controls (odds ratio, 0.38; 95% confidence interval, 0.14-1.03). The lack of support for a link between four IL-4Ralpha and IL-13 SNPs and glioblastoma may reflect the absence of associations or may result from uncontrolled confounding by haplotypes related both to those that we examined and glioblastoma. Nonetheless, the association between the T-G IL-4Ralpha haplotype and glioblastoma risk may indicate a role of immune factors in glioblastoma development.

Epidemiology of brain tumors

Brain tumors seemed to have increased in incidence over the past 30 years, but the rise probably results from use of new neuroimaging techniques. Treatments have not improved prognosis for rapidly fatal brain tumors. Established brain tumor risk factors (exposure to ionizing radiation, rare mutations of penetrant genes, and familial history) explain only a small proportion of brain tumors, and only one of these potentially is modifiable. Genetic and environmental characteristics likely play a role in familial aggregation of glioma and these factors are not identified. New concepts in brain tumor etiology and clinical management are the goal of research, with an aim at eradicating this devastating disease.

GLIOGENE an International Consortium to Understand Familial Glioma

Evidence for familial aggregation of glioma has been documented in both case-control and cohort studies and occurs apart from the well-described rare inherited genetic syndromes involving glioma: neurofibromatosis type 1 and 2, tuberous sclerosis, Turcot's syndrome, and Li-Fraumeni syndrome. Nonsyndromic glioma families have been studied but no genes have been identified in the two published linkage studies of familial glioma probably due to the small number of families. Because glioma is a rare but devastating cancer, and a family history of glioma has been observed in approximately 5% of the cases, we initiated an international consortium to identify glioma families not affected by syndromes to better understand the inherited factors related to this disease. The international consortium GLIOGENE is an acronym for "glioma gene" and includes 15 research groups in North America, Europe, and Israel to study familial glioma. The overarching goal is to characterize genes in glioma families using a genome-wide single-nucleotide polymorphism approach and conducting linkage analysis to identify new genomic regions or loci that could harbor genes important for gliomagenesis. Here, we review the rationale for studying familial glioma and our proposed strategy for the GLIOGENE study.

Tumor genomic profiling and TP53 germline mutation analysis of first-degree relative familial gliomas

About 5% of gliomas occur in a familial context, which suggests a genetic origin, but the predisposing molecular factors remain unknown in most cases. A series of nine familial gliomas were characterized with 1-megabase resolution BAC array-based comparative genomic hybridization (aCGH) together with germline sequence analysis of TP53. This series was compared with a literature series of familial gliomas and a personal series of sporadic gliomas, analyzed by chromosome CGH and aCGH, respectively. No significant difference was noted between the three populations in terms of clinical characteristics, pathologic features, and the most frequent chromosomal alterations, including loss of 1p, 10p, 10q, 13q, and 19q, and gain of 7p, 7q, 16p, 18q, 19p, 19q, 20p, and 22q. However, a genomic region located in 6q was more frequently gained in our series of familial as compared to sporadic gliomas (P=0.028). A germline TP53 mutation was observed in 1/9 cases, which suggests Li-Fraumeni syndrome. Interestingly, the Pro allele in the codon 72 of TP53 was observed in 5/9 tumors. Although familial and sporadic gliomas share very similar cytogenetic quantitative patterns, aCGH is a promising technique for the detection of small genomic differences of potential significance.

Mechanisms of disease: genetic predictors of response to treatment in brain tumors

Brain tumors are currently diagnosed on the basis of their histology. The most common types in adults are astrocytomas, oligodendrogliomas and oligoastrocytomas or mixed tumors, which almost invariably lead to death. Improvements in outcome have been elusive despite intensive research. Recent findings indicate that response to conventional therapy, at least in some cases, correlates better with genetic characteristics than histopathology. An understanding of the molecular mechanisms that underlie the malignant phenotype of gliomas also provides the possibility of rational design of molecularly targeted therapies. This approach has proved successful in other areas of oncology. As many tumors have the same types of molecular abnormalities, molecular targeted therapies developed for nonbrain tumor types might be adapted for the treatment of brain tumors. There are a number of unique problems involved in treating tumors in the brain that must be overcome. The genetic predictors of response to conventional therapies, the genes and cellular mechanisms involved in glioma development, and potential therapeutic targets are reviewed. The possibility of designing tailored molecular therapy based on the molecular characteristics of the tumors is also explored.

Some speculation on the origin of glioblastoma

Glioblastoma, the most common primary brain tumor, is also the most deadly, with median survival of about one year, which is little improved over the last five decades. Its pathogenesis is a vexing problem. Despite extensive basic and clinical scientific research, little is known regarding the cause of this disease, the genetic factors which drive its course, or any strategies which may result in effective treatment. This persistent resistance to understanding suggests to the authors that some of the fundamental assumptions regarding the disease are likely to be flawed, and that a new paradigm must be sought to replace them. This manuscript is a review of some of what is known regarding this disease, and then presents a series of hypotheses which compromise an alternative view of glioblastoma.

Epidemiology and molecular pathology of glioma

Gliomas account for almost 80% of primary malignant brain tumors, and they result in more years of life lost than do any other tumors. Glioblastoma, the most common type of glioma, is associated with very poor survival, so glioma epidemiology has focused on identifying factors that can be modified to prevent this disease. Only two relatively rare factors have so far been conclusively shown to affect glioma risk--exposure to high doses of ionizing radiation, and inherited mutations of highly penetrant genes associated with rare syndromes. In addition, preliminary evidence points to a lower glioma risk among people with allergic conditions and high levels of serum IgE. Recent research has focused on identifying germline polymorphisms associated with risk of glioma, and using molecular markers to classify glial tumors into more-homogenous groups. Because gene products probably interact with environmental factors or developmental signals to produce gliomas, large studies are needed to analyze associations between polymorphisms and glioma. Cohort studies of immune factors and glioma risk are being undertaken to validate the results of case-control studies. Studies of polymorphisms of genetic pathways with strong prior hypotheses are being planned, and whole-genome scans are being proposed to study high-risk families and case-control series. The Brain Tumor Epidemiology Consortium has been formed to co-ordinate these studies.

Primary glioblastomas and anaplastic astrocytoma in a glioma family

A 72-year-old man presented with a short duration of symptoms relating to a right fronto-parietal glioblastoma and a family history of children with brain tumours. Analysis of the patient's family tree revealed that out of seven children, he had a living son with anaplastic astrocytoma, a daughter who had died with a glioblastoma, and a son who had died with a histologically undiagnosed intrinsic brain tumour. One niece was also thought to have died from a brain tumour. All of the other affected family members had onset in their third or fourth decades. Tissue was only available from two of the affected individuals, precluding familial genetic analysis at this stage. There is no clinical evidence to support a diagnosis of a multiple cancer or neurocutaneous syndrome in this family. In view of what is known about the genetics of familial glioma, it is interesting to note the clinical evidence of both 'primary' glioblastoma and anaplastic astrocytoma in the same kindred.

Positive and negative associations of human leukocyte antigen variants with the onset and prognosis of adult glioblastoma multiforme

Associations of genetic factors with malignant gliomas have been modest. We examined the relationships of human leukocyte antigen (HLA) and related polymorphisms to glioblastoma multiforme in adult Caucasians (non-Hispanic Whites) from the San Francisco Bay area. For 155 glioblastoma multiforme patients and 157 control subjects closely matched by ethnicity, age, and gender, PCR-based techniques resolved alleles at HLA-A, -B, -C, and -DRB1 loci along with short tandem repeat polymorphisms of MICA exon 5 and TNFb. By multivariable logistic regression, B*13 and the B*07-Cw*07 haplotype were positively associated with glioblastoma multiforme (P=0.01 and <0.001, respectively), whereas Cw*01 was the only variant showing a negative association (P=0.05). Among glioblastoma multiforme patients, progression to death after diagnosis was slower in those with A*32 (relative hazard, 0.45; P<0.01) and faster in those with B*55 (relative hazard, 2.27; P<0.01). Thus, both the occurrence and the prognosis of glioblastoma multiforme could be associated with specific but different HLA genotypes. B*07 and the B*07-Cw*07 haplotype are much more common in Caucasians than other ethnic groups in the U.S., which may partially explain the higher incidence of glioblastoma multiforme in Caucasians.

The molecular epidemiology of gliomas in adults

In this paper the authors highlight recent findings from molecular epidemiology studies of glioma origin and prognosis and suggest promising paths for future research. The reasons for variation in glioma incidence according to time period of diagnosis, sex, age, ancestry and ethnicity, and geography are poorly understood, as are factors that affect prognosis. High-dose therapeutic ionizing irradiation and rare mutations in highly penetrant genes associated with certain rare syndromes—the only two established causes of glioma—can be called upon to explain few cases. Both familial aggregation of gliomas and the inverse association of allergies and immune-related conditions with gliomas have been shown consistently, but the explanations for these associations are inadequately developed or unknown. Several bio-markers do predict prognosis, but only evaluation of loss of 1p and 19q in oligodendroglial tumors are incorporated in clinical practice. Ongoing research focuses on classifying homogeneous groups of tumors on the basis of molecular markers and identifying inherited polymorphisms that may influence survival or risk. Because most cases of glioma have yet to furnish either an environmental or a genetic explanation, the greatest potential for discovery may lie in genomic studies in conjunction with continued evaluation of environmental and developmental factors. Large sample sizes and multidisciplinary teams with expertise in neuropathology, genetics, epidemiology, functional genomics, bioinformatics, biostatistics, immunology, and neurooncology are required for these studies to permit exploration of potentially relevant pathways and modifying effects of other genes or exposures, and to avoid false-positive findings. Improving survival rates for patients harboring astrocytic tumors will probably require many randomized clinical trials of novel treatment strategies.

Epidemiology and etiology of gliomas

Gliomas of astrocytic, oligodendroglial and ependymal origin account for more than 70% of all brain tumors. The most frequent (65%) and most malignant histological type is the glioblastoma. Since the introduction of computerized tomography and magnetic resonance imaging, the incidence rates of brain tumors have been rather stable, with a tendency of higher rates in highly developed, industrialized countries. Some reports indicate that Caucasians have higher incidence than black or Asian populations, but to some extent, this may reflect socio-economic differences and under-ascertainment in some regions, rather than a significant difference in genetic susceptibility. With the exception of pilocytic astrocytomas, the prognosis of glioma patients is still poor. Less than 3% of glioblastoma patients are still alive at 5 years after diagnosis, higher age being the most significant predictor of poor outcome. Brain tumors are a component of several inherited tumor syndromes, but the prevalence of these syndromes is very low. Several occupations, environmental carcinogens, and diet (N-nitroso compounds) have been reported to be associated with an elevated glioma risk, but the only environmental factor unequivocally associated with an increased risk of brain tumors, including gliomas, is therapeutic X-irradiation. In particular, children treated with X-irradiation for acute lymphoblastic leukemia show a significantly elevated risk of developing gliomas and primitive neuroectodermal tumor (PNET), often within 10 years after therapy. TP53 mutations are frequent in low-grade gliomas and secondary glioblastomas derived therefrom. Approximately 60% of mutations are located in the hot spot codons 248 and 273, and the majority of these are G:C-->A:T transitions at CpG sites. TP53 mutations are significantly more frequent in low-grade astrocytomas with promoter methylation of the O(6)-methylguanine-DNA methyltransferase repair gene, suggesting that, in addition to deamination of 5-methylcytosine, exogenous or endogenous alkylation in the O(6) position of guanine may contribute to the formation of these mutations.

Genetic insights into familial tumors of the nervous system

Nervous system tumors represent unique neoplasms that arise within the central and peripheral nervous system. While the vast majority of nervous system neoplasm occur sporadically, most of the adult and pediatric forms have a hereditary equivalent. In a little over a decade, we have seen a tremendous increase in knowledge of the primary genetic basis of many of the familial cancer syndromes that involve the nervous system, syndromes that are mostly inherited as autosomal dominant traits. In this review, we discuss the most recent findings on the genetic basis of hereditary nervous system tumors. The identification of genes associated with familial cancer syndromes has in some families enabled a "molecular diagnosis" that complements clinical assessment and allows directed cancer surveillance for those individuals determined to be at-risk for disease.