A gene subject to genomic imprinting and responsible for hereditary paragangliomas maps to chromosome 11q23-qter

Research progress on the pathogenesis of the SDHB mutation and related diseases

With the improvement of genetic testing technology in diseases in recent years, researchers have a more detailed and clear understanding of the source of cancers. Succinate dehydrogenase B (SDHB), a mitochondrial gene, is related to the metabolic activities of cells and tissues throughout the body. The mutations of SDHB have been found in pheochromocytoma, paraganglioma and other cancers, and is proved to affect the occurrence and progress of those cancers due to the important structural functions. The importance of SDHB is attracting more and more attention of researchers, however, reviews on the structure and function of SDHB, as well as on the mechanism of its carcinogenesis is inadequate. This paper reviews the relationship between SDHB mutations and related cancers, discusses the molecular mechanism of SDHB mutations that may lead to tumor formation, analyzes the mutation spectrum, structural domains, and penetrance of SDHB and sorts out some of the previously discovered diseases. For the patients with SDHB mutation, it is recommended that people in SDHB mutation families undergo regular genetic testing or SDHB immunohistochemistry (IHC). The purpose of this paper is hopefully to provide some reference and help for follow-up researches on SDHB.

The SDHD:p.H102R Variant Is Frequent in Russian Patients with Head and Neck Paragangliomas and Associated with Loss of 11p15.5 Region and Hypermethylation of H19-DMR

Head and neck paragangliomas (HNPGLs) are rare neuroendocrine neoplasms derived from the parasympathetic paraganglia of the head and neck. At least 30% of HNPGLs are linked to germline mutations, predominantly in SDHx genes. In this study, we analyzed an extended cohort of Russian patients with HNPGLs using whole-exome sequencing and found a highly frequent missense variant p.H102R in the SDHD gene. We determined this variant in 34% of the SDHD mutation carriers. This variant was associated with somatic loss of the gene wild-type allele. Data from the B allele frequency method and microsatellite and microdeletion analysis indicated evident LOH at the 11p15.5 region and potential loss of the whole of chromosome 11. We found hypermethylation of H19-DMR in all tumors, whereas differential methylation of KvDMR was mostly retained. These findings do not support the paternal transmission of SDHD:p.H102R but are in agreement with the Hensen model. Using targeted sequencing, we also studied the variant frequency in a control cohort; we found SDHD:p.H102R in 1.9% of cases, allowing us to classify this variant as pathogenic. The immunohistochemistry of SDHB showed that the SDHD:p.H102R mutation, even in combination with wild-type allele loss, does not always lead to SDH deficiency. The obtained results demonstrate the frequent variant associated with HNPGLs in a Russian population and support its pathogenicity. Our findings help with understanding the mechanism of tumorigenesis and are also important for the development of cost-effective genetic screening programs.

Somatic Mutation Profiling in Head and Neck Paragangliomas

CONTEXT

Head and neck paragangliomas (HNPGLs) are rare neoplasms with a high degree of heritability. Paragangliomas present as polygenic diseases caused by combined alterations in multiple genes; however, many driver changes remain unknown.

OBJECTIVE

The objective of the study was to analyze somatic mutation profiles in HNPGLs.

METHODS

Whole-exome sequencing of 42 tumors and matched normal tissues obtained from Russian patients with HNPGLs was carried out. Somatic mutation profiling included variant calling and utilizing MutSig and SigProfiler packages.

RESULTS

57% of patients harbored germline and somatic variants in paraganglioma (PGL) susceptibility genes or potentially related genes. Somatic variants in novel genes were found in 17% of patients without mutations in any known PGL-related genes. The studied cohort was characterized by 6 significantly mutated genes: SDHD, BCAS4, SLC25A14, RBM3, TP53, and ASCC1, as well as 4 COSMIC single base substitutions (SBS)-96 mutational signatures (SBS5, SBS29, SBS1, and SBS7b). Tumors with germline variants specifically displayed SBS11 and SBS19, when an SBS33-specific mutational signature was identified for cases without those. Beta allele frequency analysis of copy number variations revealed loss of heterozygosity of the wild-type allele in 1 patient with germline mutation c.287-2A>G in the SDHB gene. In patients with germline mutation c.A305G in the SDHD gene, frequent potential loss of chromosome 11 was observed.

CONCLUSION

These results give an understanding of somatic changes and the mutational landscape associated with HNPGLs and are important for the identification of molecular mechanisms involved in tumor development.

[Modern conceptions on neck paragangliomas]

Neck paragangliomas are orphan diseases with incidence 1:30 000-1:100 000. Life expectancy is poor in patients with distant metastasis (5-year overall survival 11.8%), whereas 5-year overall survival in patients with regional metastasis is 76.8-82.4%. Meanwhile, there is still no any reliable tool for prediction of malignant potential of paraganglioma. Above-mentioned data indicate an importance of early diagnosis and timely treatment of neck paragangliomas. Total resection of tumor in ablastic conditions is a gold standard of treatment. However, surgery is associated with a high risk of neurovascular complications and requires multidisciplinary approach. Nevertheless, new knowledge dedicated to different aspects of pathogenesis of neck paraganglioma, diagnosis and treatment arise every year. This review is devoted to modern data on neck paragangliomas.

Incomplete penetrance of a novel SDHD variation causing familial head and neck paraganglioma

Objective

Identification of variations in tumour suppressor genes encoding the tetrameric succinate dehydrogenase (SDHx) mitochondrial enzyme complex may lead to personalised therapeutic concepts for the orphan disease, familial paraganglioma (PGL) type 1‐5. We undertook to determine the causative variation in a family suffering from idiopathic early‐onset (22 ± 2 years) head and neck PGL by PCR and Sanger sequencing.

Design

Prospective genetic study.

Setting

Tertiary Referral Otolaryngology Centre.

Participants

Twelve family members.

Main outcome measures

Main outcomes were clinical analysis and SDH genotyping

Results and Conclusions

A novel heterozygous c.298delA frameshift variation in exon 3 of SDH subunit D (SDHD) was associated with a paternal transmission pattern of PGL in affected family members available to the study. Family history over five generations in adulthood indicated a variable penetrance for PGL inheritance in older generations. The c.298delA variant would cause translation of a 34‐residue C‐terminus distal to lysine residue 99 in the predicted transmembrane domain II of the full‐length sequence p.(Thr100LeufsTer35) and would affect the translation products of all protein‐coding SDHD isoforms containing transmembrane topologies required for positional integration in the inner mitochondrial membrane and complex formation. These results underly the importance of genetic screening for PGL also in cases of unclear inheritance, and variation carriers should benefit from screening and lifelong follow‐up.

Head-and-neck paragangliomas: An overview of 54 cases operated at a tertiary care center

Background:

Head-and-neck paragangliomas (HNP's) are rare autonomic neoplasms associated with high morbidity and mortality. We aimed to study epidemiology, clinicopathological correlation, and management of HNP to assist clinicians in advocating the most appropriate therapy.

Materials and Methods:

Epidemiological parameters, including age and sex distribution, clinical presentation, tumor classification, familial predisposition, multicentricity, and treatment modalities adopted, were analyzed in this retrospective analysis of 54 patients of HNP.

Results:

Age ranged from 15 to 85 years, with a female preponderance. Among all HNP, carotid body tumor (CBT) (48.1%) was the most common, followed by Glomus Jugulare (24.1%). Majority of the patients presented with neck swelling associated with nerve palsies. A preoperative neurological deficit was most commonly observed with Glomus jugulotympanicum (68.4%).

Conclusion:

CBT is the largest and most common paraganglioma in our study. The familial occurrence warrants meticulous screening for multifocality. Tumor location, neurovascular involvement, malignant potential, and patient factors should guide the designing of management options.

Hereditary Paraganglioma Syndrome Associated with SDHD Gene Mutations: A Patient with Multicentric Presentation Treated with Radiotherapy. Case Report

Introduction

Extra-adrenal paragangliomas are rare tumors arising from neuroendocrine cells. Sporadic and hereditary forms have been recognized. Among the latter, the PGL1 and PGL4 syndromes are associated with a high risk of multiple localizations. The treatment of choice for paragangliomas is surgical resection, but in some cases surgery can be difficult due to particular or multiple tumor sites or may result in severe neurological deficits. In such cases radiotherapy can be an effective alternative. In this paper we describe the case of a patient affected by hereditary paraganglioma syndrome with multicentric presentation who was treated at our center by external radiotherapy.

Case report

A 55-year-old man presented in April 2008 with multiple paragangliomas: one in the left pontocerebellar angle, two in the middle neck, one mediastinal paraaortic mass, and an abdominal paraaortic lesion. The left pontocerebellar and mediastinal tumors were treated with three-dimensional conformal radiotherapy (3D-CRT) at total doses of 50.40 Gy and 55.80 Gy, respectively. The neck lesions were treated with intensity-modulated radiotherapy (IMRT) at a total dose of 55.80 Gy. The abdominal paraaortic lesion was surgically resected.

Results

No severe acute or late toxicity as evaluated with the EORTC-RTOG scale was observed. Fourteen months after the end of radiotherapy a whole body CT scan showed that the tumor lesions were stable in size and in their relations to contiguous structures. The arterial pressure was controlled by medical therapy and urine catecholamine levels were within the normal range.

Conclusions

We believe that in patients affected by unresectable paragangliomas radiotherapy is a safe and effective alternative to surgery. The use of high-dose conformity techniques such as 3D-CRT and IMRT will allow higher local control rates with relatively few side effects thanks to the possibility of dose escalation and reduction of the amount of irradiated healthy tissues.

Human Metabolic Enzymes Deficiency: A Genetic Mutation Based Approach

One of the extreme challenges in biology is to ameliorate the understanding of the mechanisms which emphasize metabolic enzyme deficiency (MED) and how these pretend to have influence on human health. However, it has been manifested that MED could be either inherited as inborn error of metabolism (IEM) or acquired, which carries a high risk of interrupted biochemical reactions. Enzyme deficiency results in accumulation of toxic compounds that may disrupt normal organ functions and cause failure in producing crucial biological compounds and other intermediates. The MED related disorders cover widespread clinical presentations and can involve almost any organ system. To sum up the causal factors of almost all the MED-associated disorders, we decided to embark on a less traveled but nonetheless relevant direction, by focusing our attention on associated gene family products, regulation of their expression, genetic mutation, and mutation types. In addition, the review also outlines the clinical presentations as well as diagnostic and therapeutic approaches.

Instability of succinate dehydrogenase in SDHD polymorphism connects reactive oxygen species production to nuclear and mitochondrial genomic mutations in yeast

AIMS

Mitochondrial succinate dehydrogenase (SDH) is an essential complex of the electron transport chain and tricarboxylic acid cycle. Mutations in the human SDH subunit D frequently lead to paraganglioma (PGL), but the mechanistic consequences of the majority of SDHD polymorphisms have yet to be unraveled. In addition to the originally discovered yeast SDHD subunit Sdh4, a conserved homolog, Shh4, has recently been identified in budding yeast. To assess the pathogenic significance of SDHD mutations in PGL patients, we performed functional studies in yeast.

RESULTS

SDHD protein expression was reduced in SDHD-related carotid body tumor tissues. A BLAST search of SDHD to the yeast protein database revealed a novel protein, Shh4, that may have a function similar to human SDHD and yeast Sdh4. The missense SDHD mutations identified in PGL patients were created in Sdh4 and Shh4, and, surprisingly, a severe respiratory incompetence and reduced expression of the mutant protein was observed in the sdh4Δ strain expressing shh4. Although shh4Δ cells showed no respiratory-deficient phenotypes, deletion of SHH4 in sdh4Δ cells further abolished mitochondrial function. Remarkably, sdh4Δ shh4Δ strains exhibited increased reactive oxygen species (ROS) production, nuclear DNA instability, mtDNA mutability, and decreased chronological lifespan.

INNOVATION AND CONCLUSION

SDHD mutations are associated with protein and nuclear and mitochondrial genomic instability and increase ROS production in our yeast model. These findings reinforce our understanding of the mechanisms underlying PGL tumorigenesis and point to the yeast Shh4 as a good model to investigate the possible pathogenic relevance of SDHD in PGL polymorphisms.

Clinical management of paragangliomas

Paragangliomas (PGLs) are rare vascular, neuroendocrine tumors of paraganglia, which are associated with either sympathetic tissue in adrenal (pheochromocytomas (PCCs)) and extraadrenal (sympathetic paraganglioma (sPGLs)) locations or parasympathetic tissue of the head and neck paragangliomas (HNPGLs). As HNPGLs are usually benign and most tumors grow slowly, a wait-and-scan policy is often advised. However, their location in the close proximity to cranial nerves and vasculature may result in considerable morbidity due to compression or infiltration of the adjacent structures, necessitating balanced decisions between a wait-and-see policy and active treatment. The main treatment options for HNPGL are surgery and radiotherapy. In contrast to HNPGLs, the majority of sPGL/PCCs produces catecholamines, in advanced cases resulting in typical symptoms and signs such as palpitations, headache, diaphoresis, and hypertension. The state-of-the-art diagnosis and localization of sPGL/PCCs are based on measurement of plasma and/or 24-h urinary excretion of (fractionated) metanephrines and methoxytyramine (MT). sPGL/PCCs can subsequently be localized by anatomical (computed tomography and/or magnetic resonance imaging) and functional imaging studies (123I-metaiodobenzylguanidine-scintigraphy, 111In-pentetreotide scintigraphy, or positron emission tomography with radiolabeled dopamine or dihydroxyphenylalanine). Although most PGL/PCCs are benign, factors such as genetic background, tumor size, tumor location, and high MT levels are associated with higher rates of metastatic disease. Surgery is the only curative treatment. Treatment options for patients with metastatic disease are limited. PGL/PCCs have a strong genetic background, with at least one-third of all cases linked with germline mutations in 11 susceptibility genes. As genetic testing becomes more widely available, the diagnosis of PGL/PCCs will be made earlier due to routine screening of at-risk patients. Early detection of a familial PGL allows early detection of potentially malignant PGLs and early surgical treatment, reducing the complication rates of this operation.

Review of statistical methodologies for the detection of parent-of-origin effects in family trio genome-wide association data with binary disease traits

The detection of parent-of-origin effects aims to identify whether the functionality of alleles, and in turn associated phenotypic traits, depends on the parental origin of the alleles. Different parent-of-origin effects have been identified through a variety of mechanisms and a number of statistical methodologies for their detection have been proposed, in particular for genome-wide association studies (GWAS). GWAS have had limited success in explaining the heritability of many complex disorders and traits, but successful identification of parent-of-origin effects using trio (mother, father and offspring) GWAS may help shed light on this missing heritability. However, it is important to choose the most appropriate parent-of-origin test or methodology, given knowledge of the phenotype, amount of available data and the type of parent-of-origin effect(s) being considered. This review brings together the parent-of-origin detection methodologies available, comparing them in terms of power and type I error for a number of different simulated data scenarios, and finally offering guidance as to the most appropriate choice for the different scenarios.

Familial pheochromocytomas and paragangliomas

Pheochromocytomas and paragangliomas are neural crest cell tumors of the adrenal medulla and parasympathetic/sympathetic ganglia, respectively, that are often associated with catecholamine production. Genetic research over the years has led to our current understanding of the association 13 susceptibility genes with the development of these tumors. Most of the susceptibility genes are now associated with specific clinical presentations, biochemical makeup, tumor location, and associated neoplasms. Recent scientific advances have highlighted the role of somatic mutations in the development of pheochromocytoma/paraganglioma as well as the usefulness of immunohistochemistry in triaging genetic testing. We can now approach genetic testing in pheochromocytoma/paraganglioma patients in a very organized scientific way allowing for the reduction of both the financial and emotional burden on the patient. The discovery of genetic predispositions to the development of pheochromocytoma/paraganglioma not only facilitates better understanding of these tumors but will also lead to improved diagnosis and treatment of this disease.

SDHB gene mutation in a carotid body paraganglioma: case report and review of the paraganglioma syndromes

Carotid body tumors represent the most common of head and neck tumors. They account for <0.03% of all human tumors. The underlying physiology and pathogenesis of this tumor type are not well understood. Several different genetic abnormalities have been associated with the development of carotid body paragangliomas. We present a case report with an unusual genetic mutation in the SDHB gene and a review of the paraganglioma syndromes.

Succinate dehydrogenase deficiency in pediatric and adult gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) in adults are generally driven by somatic gain-of-function mutations in KIT or PDGFRA, and biological therapies targeted to these receptor tyrosine kinases comprise part of the treatment regimen for metastatic and inoperable GISTs. A minority (10-15%) of GISTs in adults, along with ∼85% of pediatric GISTs, lacks oncogenic mutations in KIT and PDGFRA. Not surprisingly these wild type (WT) GISTs respond poorly to kinase inhibitor therapy. A subset of WT GISTs shares a set of distinguishing clinical and pathological features, and a flurry of recent reports has convincingly demonstrated shared molecular characteristics. These GISTs have a distinct transcriptional profile including over-expression of the insulin-like growth factor-1 receptor, and exhibit deficiency in the succinate dehydrogenase (SDH) enzyme complex. The latter is often but not always linked to bi-allelic inactivation of SDH subunit genes, particularly SDHA. This review will summarize the molecular, pathological, and clinical connections that link this group of SDH-deficient neoplasms, and offer a view toward understanding the underlying biology of the disease and the therapeutic challenges implicit to this biology.

Mitochondrial complex II and genomic imprinting in inheritance of paraganglioma tumors

Germ line heterozygous mutations in the structural subunit genes of mitochondrial complex II (succinate dehydrogenase; SDH) and the regulatory gene SDHAF2 predispose to paraganglioma tumors which show constitutive activation of hypoxia inducible pathways. Mutations in SDHD and SDHAF2 cause highly penetrant multifocal tumor development after a paternal transmission, whereas maternal transmission rarely, if ever, leads to tumor development. This transmission pattern is consistent with genomic imprinting. Recent molecular evidence supports a model for tissue-specific imprinted regulation of the SDHD gene by a long range epigenetic mechanism. In addition, there is evidence of SDHB mRNA editing in peripheral blood mononuclear cells and long-term balancing selection operating on the SDHA gene. Regulation of SDH subunit expression by diverse epigenetic mechanisms implicates a crucial dosage-dependent role for SDH in oxygen homeostasis. This article is part of a Special Issue entitled: Respiratory complex II: Role in cellular physiology and disease.

Jugulotympanic paragangliomas: 75 years of evolution in understanding

Jugulotympanic paragangliomas were first described approximately 75 years ago. Since that time, there has been considerable evolution in knowledge of tumor biology, methods of classification, and appropriate management strategies. This paper attempts to summarize these gains in information.

Recent advances in the genetics of SDH-related paraganglioma and pheochromocytoma

The last 10 years have seen enormous progress in the field of paraganglioma and pheochromocytoma genetics. The identification of the first gene related to paraganglioma, SDHD, encoding a subunit of mitochondrial succinate dehydrogenase (SDH), was quickly followed by the identification of mutations in SDHC and SDHB. Very recently several new SDH-related genes have been discovered. The SDHAF2 gene encodes an SDH co-factor related to the function of the SDHA subunit, and is currently exclusively associated with head and neck paragangliomas. SDHA itself has now also been identified as a paraganglioma gene, with the recent identification of the first mutation in a patient with extra-adrenal paraganglioma. Another SDH-related co-factor, SDHAF1, is not currently known to be a tumor suppressor, but may shed some light on the mechanisms of tumorigenesis. An entirely novel gene associated with adrenal pheochromocytoma, TMEM127, suggests that other new paraganglioma susceptibility genes may await discovery. In addition to these recent discoveries, new techniques related to mutation analysis, including genetic analysis algorithms, SDHB immunohistochemistry, and deletion analysis by MLPA have improved the efficiency and accuracy of genetic analysis. However, many intriguing questions remain, such as the striking differences in the clinical phenotype of genes that encode proteins with an apparently very close functional relationship, and the lack of expression of SDHD and SDHAF2 mutations when inherited via the maternal line. Little is still known of the origins and causes of truly sporadic tumors, and the role of oxygen in the relationships between high-altitude, familial and truly sporadic paragangliomas remains to be elucidated.

Phaeochromocytoma: a catecholamine and oxidative stress disorder

The WHO classification of endocrine tumors defines pheochromocytoma as a tumor arising from chromaffin cells in the adrenal medulla - an intra-adrenal paraganglioma. Closely related tumors of extra-adrenal sympathetic and parasympathetic paraganglia are classified as extra-adrenal paragangliomas. Almost all pheochromocytomas and paragangliomas produce catecholamines. The concentrations of catecholamines in pheochromocytoma tissues are enormous, potentially creating a volcano that can erupt at any time. Significant eruptions result in catecholamine storms called "attacks" or "spells". Acute catecholamine crisis can strike unexpectedly, leaving traumatic memories of acute medical disaster that champions any intensive care unit. A very well-defined genotype-biochemical phenotype relationship exists, guiding proper and cost-effective genetic testing of patients with these tumors. Currently, the production of norepinephrine and epinephrine is optimally assessed by the measurement of their O-methylated metabolites, normetanephrine or metanephrine, respectively. Dopamine is a minor component, but some paragangliomas produce only this catecholamine or this together with norepinephrine. Methoxytyramine, the O-methylated metabolite of dopamine, is the best biochemical marker of these tumors. In those patients with equivocal biochemical results, a modified clonidine suppression test coupled with the measurement of plasma normetanephrine has recently been introduced. In addition to differences in catecholamine enzyme expression, the presence of either constitutive or regulated secretory pathways contributes further to the very unique mutation-dependent catecholamine production and release, resulting in various clinical presentations. Oxidative stress results from a significant imbalance between levels of prooxidants, generated during oxidative phosphorylation, and antioxidants. The gradual accumulation of prooxidants due to metabolic oxidative stress results in proto-oncogene activation, tumor suppressor gene inactivation, DNA damage, and genomic instability. Since the mitochondria serves as the main source of prooxidants, any mitochondrial impairment leads to severe oxidative stress, a major outcome of which is tumor development. In terms of cancer pathogenesis, pheochromocytomas and paragangliomas represent tumors where the oxidative phosphorylation defect due to the mutation of succinate dehydrogenase is the cause, not a consequence, of tumor development. Any succinate dehydrogenase pathogenic mutation results in the shift from oxidative phosphorylation to aerobic glycolysis in the cytoplasm (also called anaerobic glycolysis if hypoxia is the main cause of such a shift). This phenomenon, also called the Warburg effect, is well demonstrated by a positive [18F]-fluorodeoxyglycose positron emission tomography scan. Microarray studies, genome-wide association studies, proteomics and protein arrays, metabolomics, transcriptomics, and bioinformatics approaches will remain powerful tools to further uncover the pathogenesis of these tumors and their unique markers, with the ultimate goal to introduce new therapeutic options for those with metastatic or malignant pheochromocytoma and paraganglioma. Soon oxidative stress will be tightly linked to a multistep cancer process in which the mutation of various genes (perhaps in a logistic way) ultimately results in uncontrolled growth, proliferation, and metastatic potential of practically any cell. Targeting the mTORC, IGF-1, HIF and other pathways, topoisomerases, protein degradation by proteosomes, balancing the activity of protein kinases and phosphatases or even synchronizing the cell cycle before any exposure to any kind of therapy will soon become a reality. Facing such a reality today will favor our chances to "beat" this disease tomorrow.

An update on the surgical treatment of temporal bone paraganglioma

In 1982, Fisch described his results for the surgical treatment of 74 paragangliomas of the temporal bone, 5 years after his description of the infratemporal fossa approaches (types A and B). This study reviews the subsequent experience of the Department of Otolaryngology-Head and Neck Surgery of the University of Zürich with more than 136 surgically treated cases of paraganglioma of the temporal bone and discusses our current therapy 20 years after the initial description. One hundred nineteen (90%) of the patients had advanced tumors (Fisch class C or C+D), and 81 (68%) had intracranial extension. Total tumor excision was possible in 109 (82%) patients. Subtotal excision was performed in 22 (17%) patients, 21 of whom had intradural tumor invasion. In these cases, the resection was limited not by actual tumor size but by the degree of intracranial intradural tumor extension. Partial tumor excision was undertaken in only 1 patient with a C4De2Di2 tumor. The success rate in preservation of function of the lower cranial nerves was encouraging. Of the 69 patients whose facial nerve status was followed post-operatively, 81% maintained Fisch grade 76 to 100% (House-Brackman grades I and II). Analysis of follow-up data ranging from 2 to 11 years demonstrated 98% disease-free survival when total tumor extirpation was possible. In the patients who underwent subtotal or partial surgical resection there has been no subsequent tumor growth detected by either clinical or neuroradiological evaluation. We have confirmed after more than 20 years of experience that the infratemporal fossa approaches are a safe, highly effective means of surgical management of paragangliomas of the temporal bone, allowing eradication or arrest of disease with minimal morbidity. Limited intradural surgical resection in cases of very extensive tumors can greatly benefit patients for whom complete excision is not an option.

SDH mutations in cancer

The SDHA, SDHB, SDHC, SDHD genes encode the four subunits of succinate dehydrogenase (SDH; mitochondrial complex II), a mitochondrial enzyme involved in two essential energy-producing metabolic processes of the cell, the Krebs cycle and the electron transport chain. Germline loss-of-function mutations in any of the SDH genes or assembly factor (SDHAF2) cause hereditary paraganglioma/phaeochromocytoma syndrome (HPGL/PCC) through a mechanism which is largely unknown. Owing to the central function of SDH in cellular energy metabolism it is important to understand its role in tumor suppression. Here is reported an overview of genetics, clinical and molecular progress recently performed in understanding the basis of HPGL/PCC tumorigenesis.

Clinicoradiological manifestations of paraganglioma syndromes associated with succinyl dehydrogenase enzyme mutation

Background

Paragangliomas are rare tumours derived from the autonomic nervous system that have increasingly been recognised to have a genetic predisposition. Mutations of the enzyme succinyl dehydrogenase (SDH) have proven to result in paraganglioma formation. There are four subunits (A through D) that form the enzyme complex and are associated with different genophenotypic expressions of disease. SDHB and SDHD mutations are more common, whereas SDHA and SDHC mutations are rare. Patients with SDHB mutations are prone to extra-adrenal pheochromocytomas, malignant disease and extra-paraganglial neoplasia, whereas SDHD mutations have a greater propensity for multiple, benign head and neck paragangliomas.

Methods

Diagnosis of a sporadic paraganglioma or pheochromocytoma should lead to a full genetic workup of the patient and family if SDH mutations are found.

Results

Further annual screening will be required depending on the mutation, which can have a significant impact on radiologists and the resources of the radiology department.

Conclusion

We present our imaging experience with a series of patients with proven SDH mutations resulting in paragangliomas with a review of the literature.

Hereditary paragangliomas

Paragangliomas (PGL) and pheochromocytomas (PCC) are rare, usually benign tumors that originate from the neuroendocrine tissue along the paravertebral axis. Up to 35% of these tumors may be hereditary; they are associated with germline mutations in genes encoding subunits of the succinate dehydrogenase (SDH) enzyme complex in the context of the familial PGL syndromes, PGL1, 3 and 4 caused by mutations in the SDHD,SDHC and SDHB genes, respectively. Another familial PGL syndrome, PGL2, is caused by mutations in SDHAF2/SDH5, which encodes for a molecule that is an accessory to the function of the SDH enzyme and its SDHA subunit. Less frequently, mutations in the genes responsible for Von Hippel Lindau disease (VHL), multiple endocrine neoplasia type 2 (MEN2), and neurofibromatosis type 1 (NF1) are also found in patients with hereditary PGL and PCC. Recently mutations were found in the SDHA subunit in a limited number of patients with PGL and/or PCC. The SDHB, SDHC and SDHD gene mutations (but not SDHA) can also be found in patients with PGL and/or PCC and gastrointestinal stromal tumors (GISTs), also known as the Carney-Stratakis syndrome; SDHB mutations, in particular, may also predispose to thyroid and renal cancer, and possibly other tumors. A new gene was recently found to predispose to PGL and/or PCC when mutated is TMEM127. In this text, we provide an overview of the genetics of PGLs and related conditions with an emphasis on genetic risk assessment, prevention, and prognosis.

Plasma chromogranin A levels are increased in a small portion of patients with hereditary head and neck paragangliomas

CONTEXT

The majority of patients with head and neck paragangliomas (HNPGL) have biochemically silent tumours. Chromogranin A (CgA) is a tumour marker for neuroendocrine tumours.

OBJECTIVE

To assess the role of CgA as a tumour marker in patients with hereditary HNPGL.

PATIENTS AND METHODS

We included 95 consecutive patients with hereditary HNPGL for screening of plasma CgA levels and catecholamine excess by measurement of 24-h urinary excretion of (nor)metanephrine, (nor)adrenaline, VMA, dopamine and 3-methoxytyramine. In all patients with catecholamine excess, abdominal/intrathoracic paragangliomas were excluded by (123) I-MIBG scintigraphy, MRI and/or CT.

RESULTS

Plasma CgA levels were increased in only 15 of 95 patients (16%). Thirty-three of the 95 patients (35%) had increased urinary excretion rates of catecholamines. Six of these 33 patients (18%) had increased plasma CgA levels. Nine of the 62 patients (15%) with a biochemically silent tumour, i.e. no increased urinary excretion of catecholamines or their metabolites, had increased CgA levels. Increased plasma CgA levels were positively correlated with urinary excretion rates of noradrenaline (r = 0·68, P = 0·005) and normetanephrine (r = 0·68, P = 0·005). There was a positive correlation between maximal HNPGL diameter and plasma CgA levels in the 57 patients with a single HNPGL (r = 0·57, P = 0·001).

CONCLUSIONS

Plasma CgA levels are increased in only a small portion of patients with hereditary HNPGL and have limited additional value to the combination of radiological and routine biochemical assessment of patients with HNPGL. Increased plasma CgA levels are associated with increased noradrenergic activity and tumour size in patients with a single HNPGL.

The Role of Radiotherapy in the Management of Paraganglioma

Paragangliomas or glomus tumors are usually low-grade hypervascular tumors occurring in various sites of the autonomic nervous system including the carotid body, glomus vagale and glomus tympanicum. Although the grading of the tumor suggests a benign clinical course, the tumor can be locally malignant and surgical management is sometimes difficult because of postoperative functional loss and local recurrence. In addition, the operative field is generally very bloody and tissue planes are not always well-defined.

Though the optimal management of paraganglioma occurs in a multidisciplinary setting, considering the excellent local control rates with primary irradiation alone, a nonsurgical definitive approach should initially be considered.

Diagnosis and management of hereditary paraganglioma syndrome due to the F933>X67 SDHD mutation

BACKGROUND

The hereditary paraganglioma syndromes (PGLs) are autosomal dominant conditions with an increased risk for tumors of the sympathetic and parasympathetic neuroendocrine systems. The recognition of patients with hereditary PGL and identification of the responsible gene are important for the management of index patients and family members.

METHODS

We present the clinical, radiological, biochemical, and family history findings of a 15-year-old boy patient with a glomus vagale versus glomus jugulare tumor.

RESULTS

Evaluation of the family history and the patient's history led to the identification of a familial succinate dehydrogenase subunit D (SDHD) gene mutation (F933>X67), consistent with a diagnosis of hereditary PGL1. Although this family had all head and neck tumors, this SDHD mutation has previously been described in a family with primarily functional pheochromocytomas.

CONCLUSIONS

This case report highlights the variable expressivity of a single mutation in SDHD, (F933>X67). Careful and comprehensive screening is warranted for individuals at risk.

SDH mutations in tumorigenesis and inherited endocrine tumours: lesson from the phaeochromocytoma-paraganglioma syndromes

A genetic predisposition for paragangliomas and adrenal or extra-adrenal phaeochromocytomas was recognized years ago. Beside the well-known syndromes associated with an increased risk of adrenal phaeochromocytoma, Von Hippel Lindau disease, multiple endocrine neoplasia type 2 and neurofibromatosis type 1, the study of inherited predisposition to head and neck paragangliomas led to the discovery of the novel 'paraganglioma-phaeochromocytoma syndrome' caused by germline mutations in three genes encoding subunits of the succinate dehydrogenase (SDH) enzyme (SDHB, SDHC and SDHD) thus opening an unexpected connection between mitochondrial tumour suppressor genes and neural crest-derived cancers. Germline mutations in SDH genes are responsible for 6% and 9% of sporadic paragangliomas and phaeochromocytomas, respectively, 29% of paediatric cases, 38% of malignant tumours and more than 80% of familial aggregations of paraganglioma and phaeochromocytoma. The disease is characterized by autosomal dominant inheritance with a peculiar parent-of-origin effect for SDHD mutations. Life-time tumour risk seems higher than 70% with variable clinical manifestantions depending on the mutated gene. In this review we summarize the most recent knowledge about the role of SDH deficiency in tumorigenesis, the spectrum and prevalence of SDH mutations derived from several series of cases, the related clinical manifestantions including rare phenotypes, such as the association of paragangliomas with gastrointestinal stromal tumours and kidney cancers, and the biological hypotheses attempting to explain genotype to phenotype correlation.

Genetic markers of mediastinal tumors

Determination of the genetic markers by the application of new genomic methodologies has provided important insight into the pathogenesis of mediastinal disease. These new techniques have enabled scientists to uncover differential gene expression patterns between subtypes of thymomas, correlate tumor marker expression with germ cell tumors, and determine a link between the NF-kappaB and JAK/STAT pathways with Hodgkin's and non-Hodgkin's lymphoma. Despite the progress made in the understanding of genetic markers of select mediastinal tumors, significantly more investigation is required to elucidate the molecular pathways involved in the pathogenesis of these tumors.

Altered clinical course of glomus tympanicum - a case report

Glomus tumours of temporal bone are rare and usually present with symptoms of hearing loss and tinnitus. Diagnosis is often delayed due to the slow growth of the tumour. Here we present a case report of a patient diagnosed as glomus tympanicum who presented only with unilateral progressive hearing loss for the past one year and rapidly detoriating hearing loss since two months who was managed successfully.

Familial carotid body tumours: is there a role for genetic screening?

Objective:

Carotid body tumours are rare lesions which are familial in 10 per cent of cases. In this paper, we demonstrate the clinical applicability of predictive genetic testing for familial carotid body tumours.

Methods:

We report a case manifesting with multiple carotid body tumours, in which subsequent genetic testing demonstrated a germline mutation which could be traced across generations. We review the diagnosis and management of carotid body tumours in the familial setting, together with the strategies presently available to screen individuals from susceptible families.

Conclusions:

The recent advent of a predictive genetic test for familial carotid body tumours offers a novel means of pre-selecting those at risk, so as to minimise screening costs and patient morbidity. Early diagnosis of lesions is essential to allow early intervention, reducing surgical morbidity and progression to malignancy.

The genetics of paragangliomas: a review

Familial head and neck paragangliomas account for approximately 10% of all head and neck paragangliomas. There are three known genes associated with genetic susceptibility to head and neck paragangliomas: succinate dehydrogenase complex subunit 'D', 'B' and 'C' (SDHD, SDHB and SDHC). The genes most frequently implicated: SDHD and SDHB, also predispose to phaeochromocytoma. SDHD shows a complex inheritance pattern - tumours do not develop if the mutation is inherited from the mother. SDHB mutations are associated with malignant phaeochromocytoma. Patients who present with a family history of paraganglioma or phaeochromocytoma, with multiple tumours, or early onset tumours (<50 years), should be referred for genetic investigation.

A novel G106D alteration of theSDHDgene in a pedigree with familial paraganglioma

Head and neck paragangliomas are tumors derived from parasympathetic paraganglia. Familial cases account for 10% or more of these tumors, and mutations of the genes encoding subunits for the mitochondrial respiratory chain complex II, SDHD, SDHB, and SDHC, have been reported. We analyzed mutations in the all four SDH genes, SDHA through SDHD, in a Japanese family with cervical paraganglioma that include a father with bilateral tumors and his daughter with a malignant left carotid body tumor with nodal metastasis. This pedigree harbored a germline G106D alteration in exon 4 of the SDHD gene that has not previously been reported to date. The tumors of the father expressed biallelic SDHD, but the SDHD expression was highly suppressed by an unknown mechanism(s) in tumors of his daughter, and the wild-type allele was predominantly suppressed in the metastatic node. These results suggest that the missense dysfunction of SDHD prepares neoplastic condition and that expressional silencing, particularly of the wild-type allele, plays an important role in the malignant transformation of the paragangliomas. Our results may lead to a better understanding of this disease and to the development of methods for prevention of this disease.

New Advances in the Genetics of Pheochromocytoma and Paraganglioma Syndromes

The discovery of the SDH genes in 2000/2001 dramatically changed the genetics of pheochromocytoma (PHEO) and paraganglioma (PGL). Five years on, it is widely accepted that all patients with PHEO/PGL, whatever their age, should undergo genetic testing, because 25-30% of PHEOs are caused by a germline mutation in one of the five PHEO susceptibility genes. However, genetic testing should be targeted according to family and clinical history. The identification of a causal mutation modifies the management and follow-up of the patient and provides an opportunity for presymptomatic genetic testing for other family members. Moreover, the demonstration that the SDH genes, are tumor suppressor genes and that their inactivation is involved in the hypoxia-angiogenic pathway activating the transcription factor hypoxia-inducible factor (HIF) by inhibiting prolyl hydroxylases (PHDs) may lead to the identification of new therapeutic targets for these rare diseases. We discuss here these recent findings and their clinical consequences for the management of PHEO/PGL families and the future of research in this field.

Mutation analysis of SDHB and SDHC: novel germline mutations in sporadic head and neck paraganglioma and familial paraganglioma and/or pheochromocytoma

Background

Germline mutations of the SDHD, SDHB and SDHC genes, encoding three of the four subunits of succinate dehydrogenase, are a major cause of hereditary paraganglioma and pheochromocytoma, and demonstrate that these genes are classic tumor suppressors. Succinate dehydrogenase is a heterotetrameric protein complex and a component of both the Krebs cycle and the mitochondrial respiratory chain (succinate:ubiquinone oxidoreductase or complex II).

Methods

Using conformation sensitive gel electrophoresis (CSGE) and direct DNA sequencing to analyse genomic DNA from peripheral blood lymphocytes, here we describe the mutation analysis of the SDHB and SDHC genes in 37 patients with sporadic (i.e. no known family history) head and neck paraganglioma and five pheochromocytoma and/or paraganglioma families.

Results

Two sporadic patients were found to have a SDHB splice site mutation in intron 4, c.423+1G>A, which produces a mis-spliced transcript with a 54 nucleotide deletion, resulting in an 18 amino acid in-frame deletion. A third patient was found to carry the c.214C>T (p.Arg72Cys) missense mutation in exon 4 of SDHC, which is situated in a highly conserved protein motif that constitutes the quinone-binding site of the succinate: ubiquinone oxidoreductase (SQR) complex in E. coli. Together with our previous results, we found 27 germline mutations of SDH genes in 95 cases (28%) of sporadic head and neck paraganglioma. In addition all index patients of five families showing hereditary pheochromocytoma-paraganglioma were found to carry germline mutations of SDHB: four of which were novel, c.343C>T (p.Arg115X), c.141G>A (p.Trp47X), c.281G>A (p.Arg94Lys), and c.653G>C (p.Trp218Ser), and one reported previously, c.136C>T, p.Arg46X.

Conclusion

In conclusion, these data indicate that germline mutations of SDHB and SDHC play a minor role in sporadic head and neck paraganglioma and further underline the importance of germline SDHB mutations in cases of familial pheochromocytoma-paraganglioma.

The SDH mutation database: an online resource for succinate dehydrogenase sequence variants involved in pheochromocytoma, paraganglioma and mitochondrial complex II deficiency

Background

The SDHA, SDHB, SDHC and SDHD genes encode the subunits of succinate dehydrogenase (succinate: ubiquinone oxidoreductase), a component of both the Krebs cycle and the mitochondrial respiratory chain. SDHA, a flavoprotein and SDHB, an iron-sulfur protein together constitute the catalytic domain, while SDHC and SDHD encode membrane anchors that allow the complex to participate in the respiratory chain as complex II. Germline mutations of SDHD and SDHB are a major cause of the hereditary forms of the tumors paraganglioma and pheochromocytoma. The largest subunit, SDHA, is mutated in patients with Leigh syndrome and late-onset optic atrophy, but has not as yet been identified as a factor in hereditary cancer.

Description

The SDH mutation database is based on the recently described Leiden Open (source) Variation Database (LOVD) system. The variants currently described in the database were extracted from the published literature and in some cases annotated to conform to current mutation nomenclature. Researchers can also directly submit new sequence variants online. Since the identification of SDHD, SDHC, and SDHB as classic tumor suppressor genes in 2000 and 2001, studies from research groups around the world have identified a total of 120 variants. Here we introduce all reported paraganglioma and pheochromocytoma related sequence variations in these genes, in addition to all reported mutations of SDHA. The database is now accessible online.

Conclusion

The SDH mutation database offers a valuable tool and resource for clinicians involved in the treatment of patients with paraganglioma-pheochromocytoma, clinical geneticists needing an overview of current knowledge, and geneticists and other researchers needing a solid foundation for further exploration of both these tumor syndromes and SDHA-related phenotypes.

Mutations of the SDHB and SDHD genes

The succinate dehydrogenase (SDH) is a mitochondrial enzyme complex with an important role in oxydative phosphorylation and intracellular oxygene sensing and signaling. Mutations in the SDHB (1p35-36) and SDHD subunits (11q23) give rise to the paraganglioma syndromes (PGL), namely PGL 4 and PGL 1, and generate paraganglioma and pheochromocytoma. For both genes mutations have been described that result in a loss of function of the gene products. SDHBmutations were found in five of eight exons and in two introns, SDHD mutations in all four exons and one intron. Phenotypes and rate of malignancy of SDHB and SDHD seem to be different, with a higher frequency of head-and-neck tumors in SDHD and indications of a higher risk of malignancy in SDHB mutations. As routine diagnostic procedure all SDH mutation carriers should have urine catecholamine analysis as well as pelvic, abdominal, thoracic and skull/neck MRI.

SDHC mutations in hereditary paraganglioma/pheochromocytoma

Mutations in genes coding for three of the four components of mitochondrial complex II can cause paragangliomas (PGLs)/pheochromocytomas. The three genes include SDHB, -C, and -D. SDHC and SDHD anchor the catalytic subunits SDHA and -B of mitochondrial complex II in the inner mitochondrial membrane. SDHD is maternally imprinted but SDHB and -C are not. While SDHD and -- to a lesser degree -- SDHB mutations have been found in many cases of hereditary PGL, SDHC mutations are rare. This article reviews the SDHC mutations described to date and discusses possible mechanisms of tumorigenesis.

Molecular pathogenesis of skull base tumors

OBJECTIVE

To review contemporary molecular biological literature related to skull base tumor biology and tumorigenesis.

DATA SOURCES

PUBMED and Ovid literature searches were performed using keyword search. Only English language articles published between 1965 and December 4, 2003 were chosen.

STUDY SELECTION AND DATA EXTRACTION

All relevant articles from the past 8 years, as well as landmark articles in years before 1995, were retrieved and reviewed.

CONCLUSION

Consistent progress is being made toward the molecular genetic and biological basis of the most common skull base tumors. An understanding of these mechanisms will aid the neurotologist in future diagnosis and management of the lesions.

Affected-sib-pair test for linkage based on constraints for identical-by-descent distributions corresponding to disease models with imprinting

Holmans' possible triangle test for affected sib pairs has proven to be a powerful tool for linkage analysis. This test is a likelihood-ratio test for which maximization is restricted to the set of possible sharing probabilities. Here, we extend the possible triangle test to take into account genomic imprinting, which is also known as parent-of-origin effect. While the classical test without imprinting looks at whether affected sib pairs share 0, 1, or 2 alleles identical-by-descent, the likelihood-ratio test allowing for imprinting further distinguishes whether the sharing of exactly one allele is through the father or mother. Thus, if the disease gene is indeed subject to imprinting, the extended test presented here can take into account that affecteds will have inherited the mutant allele preferentially from one particular parent. We calculate the sharing probabilities at a marker locus linked to a disease susceptibility locus. Using our formulation, the constraints on these probabilities given by Dudoit and Speed ([1999] Statistics in Genetics; New York: Springer) can easily be verified. Next, we derive the asymptotic distribution of the restricted likelihood-ratio test statistic under the null hypothesis of no linkage, and give LOD-score criteria for various test sizes. We show, for various disease models, that the test allowing for imprinting has significantly higher power to detect linkage if imprinting is indeed present, at the cost of only a small reduction in power in case of no imprinting. Altogether, unlike many methods currently available, our novel model-free sib-pair test adequately models the epigenetic parent-of-origin effect, and will hopefully prove to be a useful tool for the genetic mapping of complex traits.