Genetic analysis of mitochondrial complex II subunits SDHD, SDHB and SDHC in paraganglioma and phaeochromocytoma susceptibility

High incidence of occult familial SDHD cases amongst Czech patients with head and neck paragangliomas

Introduction

Head and neck paragangliomas (HNPGLs) are rare neuroendocrine tumors, which are mostly benign in nature. Amongst all genes, Succinate Dehydrogenase Subunit D (SDHD) is the most commonly mutated in familial HNPGLs. In about 30% of HNPGLs, germline mutations in SDHD can also occur in the absence of positive family history, thus giving rise to "occult familial" cases. Our aim was to evaluate the pattern of SDHD germline mutations in Czech patients with HNPGLs.

Materials and methods

We analyzed a total of 105 patients with HNPGLs from the Otorhinolaryngology departments of 2 tertiary centers between 2006 - 2021. All underwent complex diagnostic work-up and were also consented for genetic analysis.

Results

Eighty patients aged 13-76 years were included; around 60% with multiple PGLs were males. Carotid body tumor was the most frequently diagnosed tumor. Germline SDHD mutation was found in only 12% of the Czech patients; approximately 78% of those harboring the mutation had negative family history. The mutation traits had higher affiliation for multiple tumors with nearly 70% patients of ≤ 40 years of age.

Conclusion

An SDHD mutation variant was shared amongst unrelated patients but no founder-effect was established. Our findings confirmed that the pattern of SDHD mutation distribution amongst HNPGLs in Czech Republic differs from most studies worldwide.

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.

Carotid Body Tumor: A Case Report and Review of Literature

Carotid body tumour (CBT) is a rare hypervascular tumor in the head and neck region. It develops from neural crest origin paraganglionic tissue which is an arterial chemoreceptor. It presents as a slow growing mass at the carotid bifurcation. Its optimal evaluation and treatment requires involvement of multiple specialities. Because of the high rate of neurovascular complications, resection of this tumor is challenging for surgeons. Early tumor detection, meticulous evaluation and multidisciplinary approach are vital for successful management of these tumors. A case of CBT in a 50 year-old lady managed at our centre is being reported here along with a review of literature.

Emerging Role of TCA Cycle-Related Enzymes in Human Diseases

The tricarboxylic acid (TCA) cycle is the main source of cellular energy and participates in many metabolic pathways in cells. Recent reports indicate that dysfunction of TCA cycle-related enzymes causes human diseases, such as neurometabolic disorders and tumors, have attracted increasing interest in their unexplained roles. The diseases which develop as a consequence of loss or dysfunction of TCA cycle-related enzymes are distinct, suggesting that each enzyme has a unique function. This review aims to provide a comprehensive overview of the relationship between each TCA cycle-related enzyme and human diseases. We also discuss their functions in the context of both mitochondrial and extra-mitochondrial (or cytoplasmic) enzymes.

Genetic Variants in Patients with Multiple Head and Neck Paragangliomas: Dilemma in Management

Multiple head and neck paragangliomas (HNPGLs) are neuroendocrine tumors of a mostly benign nature that can be associated with a syndrome, precipitated by the presence of a germline mutation. Familial forms of the disease are usually seen with mutations of SDHx genes, especially the SDHD gene. SDHB mutations are predisposed to malignant tumors. We found 6 patients with multiple tumors amongst 30 patients with HNPGLs during the period of 2016 to 2021. We discuss the phenotypic and genetic patterns in our patients with multiple HNPGLs and explore the management possibilities related to the disease. Fifty percent of our patients had incidental findings of HNPGLs. Twenty-one biochemically silent tumors were found. Four patients had germline mutations, and only one had a positive family history. Three out of five underwent surgery without permanent complications. Preventative measures (genetic counselling and tumor surveillance) represent the gold standard in effectively controlling the disease in index patients and their relatives. In terms of treatment, apart from surgical and radiotherapeutic interventions, new therapeutic measures such as gene targeted therapy have contributed very sparsely. With the lack of standardized protocols, management of patients with multiple HNPGLs still remains very challenging, especially in those with sporadic or malignant forms of the disease.

The Impact Of Succinate Dehydrogenase Gene (SDH) Mutations In Renal Cell Carcinoma (RCC): A Systematic Review

Introduction

Renal cell cancer (RCC) syndrome is linked to Krebs cycle compartments and their coding genes' alterations like succinate dehydrogenase genes (SDHx). Here we present a systematic review of the SDH genes’ mutations and their impact on both RCC diagnosis and prognosis.

Methods

This systematic review includes any study in which tissue samples of RCC are considered in correlation with the SDHx mutations, microsatellite instability (MSI), and protein expression. For this purpose, a systematic search of MEDLINE (PubMed), Scopus, Embase, and Web of Science databases was conducted and finally 5384 articles were recruited. All studies' content was checked to find the related ones which were 145 articles, which with data extraction were limited to nineteen.

Results

The final selected nineteen studies investigating the SDHx role in RCC tumor genesis were included, among which fifteen were mutation analysis, three were just SDHx protein expression, and two were MSI and mutation analysis studies. A total of 432 RCC patients were reported by SDH mutations, and 64 patients with MSI and SDH expression change were reported in 514 surgically resected renal epithelial tumors. The most common mutation was the single nucleotide variant rs772551056 (c.137G>A) of SDHB. For SDHC, c.380A>G presented in 48 RCC patients, and for SDHA a novel germline mutation c.2T>C: p.M1T in an occasional case of gastrointestinal stromal tumor intricate with RCC.

Conclusion

RCC as an aggressive type of kidney cancer needs some biomarkers to be diagnosed exactly. It was shown recently that the succinate dehydrogenase gene variations can provide this diagnostic and prognostic biomarker. For this purpose, SDHB rs772551056 associated with its protein expression alterations can be taken into account. It is possible that a novel mutation of SDHA (c.2T>C: p.M1T) can provide evidence of GIST associated with RCC as well.

Clinical Practice Guidance: Surveillance for phaeochromocytoma and paraganglioma in paediatric succinate dehydrogenase gene mutation carriers

The succinate dehydrogenase (SDH) enzyme complex functions as a key enzyme coupling the oxidation of succinate to fumarate in the citric acid cycle. Inactivation of this enzyme complex results in the cellular accumulation of the oncometabolite succinate, which is postulated to be a key driver in tumorigenesis. Succinate accumulation inhibits 2-oxoglutarate-dependent dioxygenases, including DNA and histone demethylase enzymes and hypoxic gene response regulators. Biallelic inactivation (typically resulting from one inherited and one somatic event) at one of the four genes encoding the SDH complex (SDHA/B/C/D) is the most common cause for SDH deficient (dSDH) tumours. Germline mutations in the SDHx genes predispose to a spectrum of tumours including phaeochromocytoma and paraganglioma (PPGL), wild type gastrointestinal stromal tumours (wtGIST) and, less commonly, renal cell carcinoma and pituitary tumours. Furthermore, mutations in the SDHx genes, particularly SDHB, predispose to a higher risk of malignant PPGL, which is associated with a 5-year mortality of 50%. There is general agreement that biochemical and imaging surveillance should be offered to asymptomatic carriers of SDHx gene mutations in the expectation that this will reduce the morbidity and mortality associated with dSDH tumours. However, there is no consensus on when and how surveillance should be performed in children and young adults. Here, we address the question: "What age should clinical, biochemical and radiological surveillance for PPGL be initiated in paediatric SDHx mutation carriers?".

Concomitant paraganglioma and thyroid carcinoma: A case report

BACKGROUND

Paraganglioma/pheochromocytoma and medullary thyroid carcinoma can coexist and are often found in multiple endocrine neoplasia (MEN). However, very few cases highlight papillary thyroid carcinoma. We present herein a rare case of head and neck paraganglioma associated with papillary thyroid carcinoma.

CASE SUMMARY

A 51-year-old man presented to our department with right-sided neck swelling and hypertension. Physical examination showed neck masses with obvious pulsation. Concentrations of serum calcium, phosphorus, parathormone, thyroid stimulating hormone, free thyroxine, and calcitonin were within normal limits. Enhanced computed tomography revealed an irregular solid nodule, located in the carotid artery bifurcation. A low-density nodule of the thyroid isthmus with a spot-like dense shadow was also detected. The diagnosis of carotid body tumor was raised and an ultrasound-guided fine needle aspiration biopsy of the thyroid nodule revealed papillary thyroid carcinoma. The patient underwent surgery for lesion excision, total thyroidectomy, and neck dissection, and the pathology was reported as paraganglioma and papillary carcinoma. Genetic studies showed negative results for germline mutation of succinate dehydrogenase subunit D on 11q23. He was treated with ¹³¹I after surgery and remained disease-free so far.

CONCLUSION

The presence of concomitant paraganglioma and thyroid papillary carcinoma could be either coincidental or a result of an unknown mutation.

Can subunit-specific phenotypes guide surveillance imaging decisions in asymptomatic SDH mutation carriers?

OBJECTIVE

With the discovery that familial phaeochromocytoma and paraganglioma syndrome can be caused by mutations in each subunit of the succinate dehydrogenase enzyme (SDH), has come the recognition that mutations in the individual subunits have their own distinct natural histories. Increased genetic screening is leading to the identification of increasing numbers of, mostly asymptomatic, gene mutation carriers and the implementation of screening strategies for these individuals. Yet there is, to date, no international consensus regarding screening strategies for asymptomatic carriers.

DESIGN

A comprehensive PubMed search from 1/1/2000 to 28/2/2018 was undertaken using multiple search terms and subsequently a manual review of references in identified papers to identify all clinically relevant cases and cohorts. In this review, the accumulated, published experience of phenotype and malignancy risks of individual SDH subunits is analysed. Where possible screening results for asymptomatic SDH mutation carriers have been analysed separately to define the penetrance in asymptomatic carriers (asymptomatic penetrance).

RESULTS

The combined data confirms that "asymptomatic penetrance" is highest for SDHD and when there is penetrance, the most likely site to develop a PGL is head and neck (SDHD) and extra-adrenal abdominal (SDHB). However, the risk in SDHB carriers of developing HNPGL is also high (35.5%) and a PCC is low (15.1%), and in SDHD carriers there is a high risk of developing a PCC (35.8%) or abdominal PGL (9.4%) and a small, but significant risk at other sympathetic sites. The data suggest that the risk of malignant transformation is the same for both PCC and extra-adrenal abdominal PGLs (30%-35%) in SDHB carriers. In SDHD carriers, the risk of malignant transformation was highest in HNPGLs (7.5%) and similar for sympathetic sites (3.8%-5.2%).

CONCLUSIONS

Using this data, we suggest surveillance screening of asymptomatic carriers can be tailored to the underlying SDH subunit and review possible surveillance programmes.

The spectrum of SDHD mutations in Russian patients with head and neck paraganglioma

AIM OF THE STUDY

It was found that the mutations in the SDHD gene, encoding one of subunits of the succinate dehydrogenase complex, lead to the development of head and neck paraganglioma (HNPGL). We analyzed this gene in 91 patients with HNPGL from Russia.

MATERIALS AND METHODS

DNA was isolated from the whole blood. A screening for mutations was performed by Sanger sequencing.

RESULTS

We revealed three missense mutations that have been described previously: p.Pro81Leu, p.His102Arg, p.Tyr114Cys. Moreover, we identified a novel potentially pathogenic variant (p.Trp105*).

CONCLUSIONS

We found that mutations in the SDHD gene were less common in Russian patients compared with the majority of European populations. It was shown that the p.His102Arg mutation is a major mutation in Russia. We confirmed the previous suggestion that a bilateral localization of the tumor and the carotid type represent a marker of the genetically determined form of HNPGL.

A Unique Case of Metastatic, Functional, Hereditary Paraganglioma Associated With an SDHC Germline Mutation

CONTEXT

Mutations in genes encoding for the succinate dehydrogenase (SDH) complex are linked to hereditary paraganglioma syndromes. Paraganglioma syndrome 3 is associated with mutations in SDHC and typically manifests as benign, nonfunctional head and neck paragangliomas.

DESIGN

We describe a case of a 51-year-old woman who initially presented with diarrhea and hypertension and was found to have a retroperitoneal mass, which was resected with a pathology consistent with paraganglioma. Five years later, her symptoms recurred, and she was found to have new retroperitoneal lymphadenopathy and lytic lesions in the first lumbar vertebral body and the right iliac crest, which were visualized on CT scan and octreoscan but not on iodine-123-meta-iodobenzylguanidine (123I-MIBG) and bone scans. She had significantly elevated 24-hour urine norepinephrine and dopamine. The patient received external beam radiation and a series of different antineoplastic agents. Her disease progressed, and she eventually expired within 2 years. Genetic testing revealed a heterozygous SDHC c.43C>T, p.Arg15X mutation, which was also detected in her daughter and her grandson, both of whom have no biochemical or imaging evidence of paraganglioma syndrome yet.

CONCLUSION

We report a unique case of functional, metastatic abdominal paraganglioma associated with SDHC germline mutation. Our case exemplifies that SDHC germline mutation has variable penetrance, which may manifest with an aggressive biology that could be missed by a 123I-MIBG scan.

Tumour risks and genotype-phenotype correlations associated with germline variants in succinate dehydrogenase subunit genes SDHB, SDHC and SDHD

BACKGROUND

Germline pathogenic variants in SDHB/SDHC/SDHD are the most frequent causes of inherited phaeochromocytomas/paragangliomas. Insufficient information regarding penetrance and phenotypic variability hinders optimum management of mutation carriers. We estimate penetrance for symptomatic tumours and elucidate genotype-phenotype correlations in a large cohort of SDHB/SDHC/SDHD mutation carriers.

METHODS

A retrospective survey of 1832 individuals referred for genetic testing due to a personal or family history of phaeochromocytoma/paraganglioma. 876 patients (401 previously reported) had a germline mutation in SDHB/SDHC/SDHD (n=673/43/160). Tumour risks were correlated with in silico structural prediction analyses.

RESULTS

Tumour risks analysis provided novel penetrance estimates and genotype-phenotype correlations. In addition to tumour type susceptibility differences for individual genes, we confirmed that the SDHD:p.Pro81Leu mutation has a distinct phenotype and identified increased age-related tumour risks with highly destabilising SDHB missense mutations. By Kaplan-Meier analysis, the penetrance (cumulative risk of clinically apparent tumours) in SDHB and (paternally inherited) SDHD mutation-positive non-probands (n=371/67 with detailed clinical information) by age 60 years was 21.8% (95% CI 15.2% to 27.9%) and 43.2% (95% CI 25.4% to 56.7%), respectively. Risk of malignant disease at age 60 years in non-proband SDHB mutation carriers was 4.2%(95% CI 1.1% to 7.2%). With retrospective cohort analysis to adjust for ascertainment, cumulative tumour risks for SDHB mutation carriers at ages 60 years and 80 years were 23.9% (95% CI 20.9% to 27.4%) and 30.6% (95% CI 26.8% to 34.7%).

CONCLUSIONS

Overall risks of clinically apparent tumours for SDHB mutation carriers are substantially lower than initially estimated and will improve counselling of affected families. Specific genotype-tumour risk associations provides a basis for novel investigative strategies into succinate dehydrogenase-related mechanisms of tumourigenesis and the development of personalised management for SDHB/SDHC/SDHD mutation carriers.

Outcomes of annual surveillance imaging in an adult and paediatric cohort of succinate dehydrogenase B mutation carriers

OBJECTIVE

For 'asymptomatic carriers' of the succinate dehydrogenase subunit B (SDHB) gene mutations, there is currently no consensus as to the appropriate modality or frequency of surveillance imaging. We present the results of a surveillance programme of SDHB mutation carriers.

DESIGN

Review of clinical outcomes of a surveillance regimen in patients identified to have an SDHB gene mutation, based on annual MRI, in a single UK tertiary referral centre.

PATIENTS

A total of 92 patients were identified with an SDHB gene mutation. a total of 27 index patients presented with symptoms, and 65 patients were identified as asymptomatic carriers.

MEASUREMENTS

Annual MRI of the abdomen, with alternate year MRI of the neck, thorax and pelvis. Presence of an SDHB-related tumour included paraganglioma (PGL), phaeochromocytoma (PCC), renal cell carcinoma (RCC) and gastrointestinal stromal tumour (GIST).

RESULTS

A total of 43 PGLs, eight PCCs and one RCC occurred in the 27 index patients (23 solitary, four synchronous, five metachronous). A further 15 SDHB-related tumours (11 PGLs, three RCCs, one GIST) were identified in the asymptomatic carriers on surveillance screening (25% of screened carriers): 10 on the first surveillance imaging and five on subsequent imaging 2-6 years later. A total of 11 patients had malignant disease.

CONCLUSIONS

SDHB-related tumours are picked up as early as 2 years after initial negative surveillance scan. We believe the high malignancy rate and early identification rate of tumours justifies the use of 1-2 yearly imaging protocols and MRI-based imaging could form the mainstay of surveillance in this patient group thereby minimizing radiation exposure.

Rapid-sequence MRI for long-term surveillance for paraganglioma and phaeochromocytoma in patients with succinate dehydrogenase mutations

BACKGROUND

Patients with SDHx mutations need long-term radiological surveillance for the development of paragangliomas and phaeochromocytomas, but no longitudinal data exist. The aim of the study was to assess the performance of rapid-sequence non-contrast magnetic resonance imaging (MRI) in the long-term monitoring of patients with SDHx mutations.

METHODS

Retrospective study between 2005 and 2015 at a University Hospital and regional endocrine genetics referral centre. Clinical and imaging data of 47 patients with SDHx mutations (SDHB (36), SDHC (6) and SDHD (5)) who had surveillance for detection of paragangliomas by rapid-sequence non-contrast MRI (base of skull to pubic symphysis) were collected.

RESULTS

Twelve index cases (nine SDHB, one SDHC and two SDHD) and 35 mutation-positive relatives were monitored for a mean of 6.4 years (range 3.1-10.0 years). Mean age at the end of the study: SDHB 46.9 ± 17.6 years; SDHC 42.3 ± 24.4 years; SDHD 54.9 ± 10.6 years. On excluding imaging at initial diagnosis of index cases, 42 patients underwent 116 rapid-sequence MRI scans: 83 scans were negative and 31 scans were positive for sPGL/HNPGL in 13 patients. Most patients had multiple scans (n = number of patients (number of rapid-sequence MRI scans during screening)): n = 9 (2), n = 20 (3), n = 6 (4), n = 1 (6). Nine patients (three index) were diagnosed with new paragangliomas during surveillance and non-operated tumour size was monitored in nine patients. There were two false-positive scans (1.6%). Scans were repeated every 27 ± 9 months.

CONCLUSIONS

Biannual rapid-sequence non-contrast MRI is effective to monitor patients with SDHx mutations for detection of new tumours and monitoring of known tumours.

Primary Mitochondrial Disease and Secondary Mitochondrial Dysfunction: Importance of Distinction for Diagnosis and Treatment

Mitochondrial disease refers to a heterogeneous group of disorders resulting in defective cellular energy production due to abnormal oxidative phosphorylation (oxphos). Primary mitochondrial disease (PMD) is diagnosed clinically and ideally, but not always, confirmed by a known or indisputably pathogenic mitochondrial DNA (mtDNA) or nuclear DNA (nDNA) mutation. The PMD genes either encode oxphos proteins directly or they affect oxphos function by impacting production of the complex machinery needed to run the oxphos process. However, many disorders have the 'mitochondrial' phenotype without an identifiable mtDNA or nDNA mutation or they have a variant of unknown clinical significance. Secondary mitochondrial dysfunction (SMD) can be caused by genes encoding neither function nor production of the oxphos proteins and accompanies many hereditary non-mitochondrial diseases. SMD may also be due to nongenetic causes such as environmental factors. In our practice, we see many patients with clinical signs of mitochondrial dysfunction based on phenotype, biomarkers, imaging, muscle biopsy, or negative/equivocal mtDNA or nDNA test results. In these cases, it is often tempting to assign a patient's phenotype to 'mitochondrial disease', but SMD is often challenging to distinguish from PMD. Fortunately, rapid advances in molecular testing, made possible by next generation sequencing, have been effective at least in some cases in establishing accurate diagnoses to distinguish between PMD and SMD. This is important, since their treatments and prognoses can be quite different. However, even in the absence of the ability to distinguish between PMD and SMD, treating SMD with standard treatments for PMD can be effective. We review the latest findings regarding mitochondrial disease/dysfunction and give representative examples in which differentiation between PMD and SMD has been crucial for diagnosis and treatment.

Dichloroacetate stimulates changes in the mitochondrial network morphology via partial mitophagy in human SH-SY5Y neuroblastoma cells

Dichloroacetate (DCA) is beneficial in cancer therapy because it induces apoptosis and decreases cancer growth in vitro and in vivo without affecting non-cancer cells. DCA stimulates the activity of the enzyme pyruvate dehydrogenase by inhibiting pyruvate dehydrogenase kinase. Consequently, DCA promotes oxidative phosphorylation after glycolysis. Therefore, DCA produces changes in energy metabolism that could affect the mitochondrial network and mitophagy. This investigation determined the effects of DCA treatment on mitophagy in human neuroblastoma SH-SY5Y cells. SH-SY5Y cells were cultured and distributed into 3 groups: control, NH4Cl and chloroquine. Each group was treated with DCA at 0, 5, 30 and 60 mM for 16 h. Samples were analyzed for cell viability, mtDNA copy number, mitochondrial network morphology and expression of key proteins involved in mitochondrial dynamics, such as LC3b, FIS1, OPA1, PARKIN and PINK1. In all groups, DCA caused a decrease in cell viability, an induction of autophagy in a dose-dependent manner and a decrease in Tim23, FIS1 and PARKIN protein expression, leading to profound morphological changes in the mitochondrial network resulting in shorter and more fragmented filaments. However, TFAM protein levels remained unchanged. Similarly, the mitochondrial copy number was not significantly different among the treatment groups. In conclusion, DCA induces mitophagy and remodeling of the mitochondrial network. In this remodeling, DCA induces a decrease in the expression of key proteins involved in protein degradation and mitochondrial dynamics but does not significantly affect the mtDNA density. Blocking late phase autophagy increases the effects of DCA, suggesting that autophagy protects the cell, at least partially, against DCA.

Components of cancer metabolism and therapeutic interventions

All forms of life share a common indispensible need of energy. The requirement of energy is necessary for an organism not only to survive but also to thrive. The metabolic activities in normal cells rely predominately on mitochondrial oxidative phophorylation for energy generation in the form of ATP. On the contrary, cancer cells predominately rely on glycolysis rather than oxidative phosphorylation. It is long believed that an impairment of mitochondrial oxidative phosphorylation is the cause of this glycolytic phenotype observed in cancers. However, studies in cancer metabolism have revealed that mitochondrial function in many cancers is intact. It has also been observed that cancers utilize various forms of metabolism. The various metabolic phenotypes that are employed by cancer cells have a common purpose, to balance macromolecular biosynthesis and sufficient ATP production in order to support the rapid proliferation rate characteristic of these aberrant cells. These metabolic pathways are attractive targets for possible therapeutic interventions and currently research is underway to meet this end. More importantly, normal cells have essentially the same metabolic requirements as cancer cells so finding an approach to target these metabolic pathways without incurring detrimental effects on normal tissues remains the challenge.

Current views on cell metabolism in SDHx-related pheochromocytoma and paraganglioma

Warburg's metabolic hypothesis is based on the assumption that a cancer cell's respiration must be under attack, leading to its damage, in order to obtain increased glycolysis. Although this may not apply to all cancers, there is some evidence proving that primarily abnormally functioning mitochondrial complexes are indeed related to cancer development. Thus, mutations in complex II (succinate dehydrogenase (SDH)) lead to the formation of pheochromocytoma (PHEO)/paraganglioma (PGL). Mutations in one of the SDH genes (SDHx mutations) lead to succinate accumulation associated with very low fumarate levels, increased glutaminolysis, the generation of reactive oxygen species, and pseudohypoxia. This results in significant changes in signaling pathways (many of them dependent on the stabilization of hypoxia-inducible factor), including oxidative phosphorylation, glycolysis, specific expression profiles, as well as genomic instability and increased mutability resulting in tumor development. Although there is currently no very effective therapy for SDHx-related metastatic PHEOs/PGLs, targeting their fundamental metabolic abnormalities may provide a unique opportunity for the development of novel and more effective forms of therapy for these tumors.

Comparative analysis of some aspects of mitochondrial metabolism in differentiated and undifferentiated neuroblastoma cells

The aim of the present study is to clarify some aspects of the mechanisms of regulation of mitochondrial metabolism in neuroblastoma (NB) cells. Experiments were performed on murine Neuro-2a (N2a) cell line, and the same cells differentiated by all-trans-retinoic acid (dN2a) served as in vitro model of normal neurons. Oxygraphy and Metabolic Control Analysis (MCA) were applied to characterize the function of mitochondrial oxidative phosphorylation (OXPHOS) in NB cells. Flux control coefficients (FCCs) for components of the OXPHOS system were determined using titration studies with specific non-competitive inhibitors in the presence of exogenously added ADP. Respiration rates of undifferentiated Neuro-2a cells (uN2a) and the FCC of Complex-II in these cells were found to be considerably lower than those in dN2a cells. Our results show that NB is not an exclusively glycolytic tumor and could produce a considerable part of ATP via OXPHOS. Two important enzymes - hexokinase-2 and adenylate kinase-2 can play a role in the generation of ATP in NB cells. MCA has shown that in uN2a cells the key sites in the regulation of OXPHOS are complexes I, II and IV, whereas in dN2a cells complexes II and IV. Results obtained for the phosphate and adenine nucleotide carriers showed that in dN2a cells these carriers exerted lower control over the OXPHOS than in undifferentiated cells. The sum of FCCs for both types of NB cells was found to exceed significantly that for normal cells suggesting that in these cells the respiratory chain was somehow reorganized or assembled into large supercomplexes.

Hypoxia-inducible factor signaling in pheochromocytoma: turning the rudder in the right direction

Many solid tumors, including pheochromocytoma (PHEO) and paraganglioma (PGL), are characterized by a (pseudo)hypoxic signature. (Pseudo)hypoxia has been shown to promote both tumor progression and resistance to therapy. The major mediators of the transcriptional hypoxic response are hypoxia-inducible factors (HIFs). High levels of HIFs lead to transcription of hypoxia-responsive genes, which are involved in tumorigenesis. PHEOs and PGLs are catecholamine-producing tumors arising from sympathetic- or parasympathetic-derived chromaffin tissue. In recent years, substantial progress has been made in understanding the metabolic disturbances present in PHEO and PGL, especially because of the identification of some disease-susceptibility genes. To date, fifteen PHEO and PGL susceptibility genes have been identified. Based on the main transcription signatures of the mutated genes, PHEOs and PGLs have been divided into two clusters, pseudohypoxic cluster 1 and cluster 2, rich in kinase receptor signaling and protein translation pathways. Although these two clusters seem to show distinct signaling pathways, recent data suggest that both clusters are interconnected by HIF signaling as the important driver in their tumorigenesis, and mutations in most PHEO and PGL susceptibility genes seem to affect HIF-α regulation and its downstream signaling pathways. HIF signaling appears to play an important role in the development and growth of PHEOs and PGLs, which could suggest new therapeutic approaches for the treatment of these tumors.

Nervous system involvement in von Hippel-Lindau disease: pathology and mechanisms

Patients with von Hippel-Lindau disease carry a germline mutation of the Von Hippel-Lindau (VHL) tumor-suppressor gene. We discuss the molecular consequences of loss of VHL gene function and their impact on the nervous system. Dysfunction of the VHL protein causes accumulation and activation of hypoxia inducible factor (HIF) which can be demonstrated in earliest stages of tumorigenesis and is followed by expression of VEGF, erythropoietin, nitric oxide synthase and glucose transporter 1 in VHL-deficient tumor cells. HIF-independent functions of VHL, epigenetic inactivation of VHL, pVHL proteostasis, and links between loss of VHL function and developmental arrest are also described. A most intriguing feature in VHL disease is the occurrence of primary hemangioblastic tumors in the nervous system, the origin of which has not yet been entirely clarified, and current hypotheses are discussed. Endolymphatic sac tumors may extend into the brain, but originally arise from proliferation of endolymphatic duct/sac epithelium; the exact nature of the proliferating epithelial cell, however, also has remained unclear, as well as the question why tumors almost consistently develop in the intraosseous portion of the endolymphatic sac/duct only. The epitheloid clear cell morphology of both advanced hemangioblastoma and renal clear cell carcinoma can make the differential diagnosis challenging, recent developments in immunohistochemical differentiation are discussed. Finally, metastasis to brain may not only be caused by renal carcinoma, but may derive from VHL disease-associated pheochromocytoma/paraganglioma, or pancreatic neuroendocrine tumor.

Role of hypoxia and HIF2α in development of the sympathoadrenal cell lineage and chromaffin cell tumors with distinct catecholamine phenotypic features

Hypoxia has wide-ranging impact in normal physiology and disease processes. This stimulus evokes changes in gene expression mediated by transcription factors termed hypoxia-inducible factors (HIFs) that affect numerous processes: angiogenesis, cell survival, cellular metabolism, stem cell self-renewal and multipotency, migration, invasiveness, and metastatic progression in tumor cells. Over the past decade, increasing numbers of reports have emerged documenting differential roles of HIF1α and HIF2α in these processes. In cells of the sympathoadrenal lineage, both HIFs differentially mediate influences of hypoxia on catecholamine synthesis and secretion, but HIF2α signaling has particularly prominent functions in regulating developmental processes of growth and differentiation. This chapter discusses the role of HIF2α and HIF1α in the context of the development, phenotypic features, and functions of chromaffin cells. Moreover, current knowledge about tumor formation in cells of the sympathoadrenal lineage, leading to catecholamine-producing pheochromocytomas and paragangliomas, is analyzed in the light of the HIF2α signaling network.

Combined blockade of signalling pathways shows marked anti-tumour potential in phaeochromocytoma cell lines

Currently, there is no completely effective therapy available for metastatic phaeochromocytomas (PCCs) and paragangliomas. In this study, we explore new molecular targeted therapies for these tumours, using one more benign (mouse phaeochromocytoma cell (MPC)) and one more malignant (mouse tumour tissue (MTT)) mouse PCC cell line - both generated from heterozygous neurofibromin 1 knockout mice. Several PCC-promoting gene mutations have been associated with aberrant activation of PI3K/AKT, mTORC1 and RAS/RAF/ERK signalling. We therefore investigated different agents that interfere specifically with these pathways, including antagonism of the IGF1 receptor by NVP-AEW541. We found that NVP-AEW541 significantly reduced MPC and MTT cell viability at relatively high doses but led to a compensatory up-regulation of ERK and mTORC1 signalling at suboptimal doses while PI3K/AKT inhibition remained stable. We subsequently investigated the effect of the dual PI3K/mTORC1/2 inhibitor NVP-BEZ235, which led to a significant decrease of MPC and MTT cell viability at doses below 50 nM but again increased ERK signalling. Accordingly, we next examined the combination of NVP-BEZ235 with the established agent lovastatin, as this has been described to inhibit ERK signalling. Lovastatin alone significantly reduced MPC and MTT cell viability at therapeutically relevant doses and inhibited both ERK and AKT signalling, but increased mTORC1/p70S6K signalling. Combination treatment with NVP-BEZ235 and lovastatin showed a significant additive effect in MPC and MTT cells and resulted in inhibition of both AKT and mTORC1/p70S6K signalling without ERK up-regulation. Simultaneous inhibition of PI3K/AKT, mTORC1/2 and ERK signalling suggests a novel therapeutic approach for malignant PCCs.

Signaling pathways in pheochromocytomas and paragangliomas: prospects for future therapies

There is currently no completely effective therapy available for metastatic pheochromocytomas or paragangliomas. Increasing understanding of the germline and somatic mutations leading to pheochromocytoma and paraganglioma development has revealed crucial insights into the molecular pathology of these tumors. A detailed understanding of the molecular pathway alterations giving rise to pheochromocytomas and paragangliomas should allow for the exploration and development of new effective molecular-targeted therapy options for this rare but frequently fatal malignancy. Molecular analysis has shown that pheochromocytoma/paraganglioma-promoting gene mutations can be divided into two major groups-clusters 1 and 2-following two different routes to tumorigenesis. Cluster 1 mutations are associated with pseudohypoxia and aberrant VEGF signaling while cluster 2 mutations are associated with abnormal activation of kinase signaling pathways such as PI3 kinase/AKT, RAS/RAF/ERK, and mTORC1/p70S6K suggesting relevant targets for novel molecular-targeted therapy approaches which will be discussed in detail in this chapter.

Genetic-clinical profile of subjects with apparently sporadic extra-adrenal paragangliomas

BACKGROUND

Mutations in the genes encoding B, C, and D subunits of the succinate dehydrogenase (SDH) are involved in the pathogenesis of familial paraganglioma (PGL) syndrome. Many subjects with apparently sporadic extra-adrenal paragangliomas are found to be carrier for SDH mutation.

OBJECTIVE

Here we describe four subjects with apparently sporadic extra-adrenal paragangliomas with newly identified mutations in the SDH subunit B and the related clinical phenotype.

METHODS

Gene sequencing was performed to search for mutations in the SDHB (all exons), SDHC (all exons), and SDHD (all exons) genes as well as VHL (all exons) and RET (10, 11, 13, 14, 15, 16 exons) genes in all four index cases. A complete clinical, biochemical, and instrumental work-up was performed.

RESULTS

Three subjects were found to be affected with a nonsense SDHB germline mutation (Q30X, Y61X, and W201X, respectively). These mutations are predicted to encode for a truncated SDHB protein. The fourth subject presented a S195del frameshift mutation, causing a deletion of the codon AGC, encoding for a serine. Clinical presentation and course of each patient is described.

CONCLUSIONS

Extra-adrenal paragangliomas, localized in the sympathetic ganglia (in the posterior thorax or in the abdomen), are very often SDHB-inherited form rather than sporadic tumor. Our data confirm the importance of genetic screening in patients affected with paragangliomas and enlarge the list of mutations responsible for the presence of these tumors.

A novel SDHD mutation associated with neck paraganglioma

The aim of this study was to describe a previously unreported mutation in the SDHD gene, which has been linked to familial paraganglioma. Clinical data were collected from all members of the family, which had four siblings affected with paraganglioma. For the index patient, genomic DNA extraction from whole blood was performed using the High Pure PCR Template Preparation kit. The nucleotide sequence in the index patient revealed a deletion in the SDHD gene, c.165_169 + 14del. The loss of nucleotides in the DNA led to production of an anomalous protein. RNA analysis showed the absence of exon 2 in the sequence that corresponded to the mRNA from the index case. Genetic testing of this deletion was extended to the symptomatic and asymptomatic brothers and sisters of the index patient and other family members at risk. The deletion was detected in both symptomatic brothers, in accordance with their phenotype, but not in the asymptomatic sister. In the other asymptomatic brother (II.7) the deletion was detected and magnetic resonance angiography revealed the vascular characteristics of two tumors in both carotid bifurcations. Thus, we report a novel punctual mutation in the SDHD gene, which is related to familial paraganglioma: the deletion was c.165_169 + 14del.

Minireview: the busy road to pheochromocytomas and paragangliomas has a new member, TMEM127

Characterization of the entire spectrum of cancer-associated genetic disruptions is an overarching goal of contemporary and future oncology and can inform on patient diagnosis, treatment, and surveillance. Hereditary endocrine tumors, by having the potential to reveal the cancer's primary molecular defect, have been especially informative in this realm. Within this group, pheochromocytomas and paragangliomas, neural crest-derived, catecholamine-secreting tumors have come to represent true conduits for gene discovery. About one-third of pheochromocytomas and paragangliomas are now known to result from germline mutations in one of at least eight genes that belong to a variety of functional classes. Greater understanding of the molecular signals transduced by these genes and their respective mutants has advanced our understanding of kinase signaling pathways, hypoxia regulation, and the link between metabolic disruptions and cell growth. A new susceptibility gene without homology to other functional classes has been recently identified and encodes for a three-spanner transmembrane protein, transmembrane protein 127 (TMEM127). Initial insights from in vitro and patient data suggest that this candidate tumor suppressor is linked to the endosomal system and the mechanistic target of rapamycin [formerly mammalian target of rapamycin (mTOR)] pathway, and that mutation carriers often have clinical features that are typically associated with sporadic forms of pheochromocytoma. Functional characterization of transmembrane protein 127 (TMEM127) and discovery of additional pheochromocytoma/paraganglioma susceptibility genes is likely to shed light on our understanding of these tumors and extend these insights to other cancers.

Succinate dehydrogenase gene mutations are strongly associated with paraganglioma of the organ of Zuckerkandl

Organ of Zuckerkandl paragangliomas (PGLs) are rare neuroendocrine tumors that are derived from chromaffin cells located around the origin of the inferior mesenteric artery extending to the level of the aortic bifurcation. Mutations in the genes encoding succinate dehydrogenase subunits (SDH) B, C, and D (SDHx) have been associated with PGLs, but their contribution to PGLs of the organ of Zuckerkandl PGLs is not known. We aimed to describe the clinical presentation of patients with PGLs of the organ of Zuckerkandl and investigate the prevalence of SDHx mutations and other genetic defects among them. The clinical characteristics of 14 patients with PGL of the organ of Zuckerkandl were analyzed retrospectively; their DNA was tested for SDHx mutations and deletions. Eleven out of 14 (79%) patients with PGLs of the organ of Zuckerkandl were found to have mutations in the SDHB (9) or SDHD (2) genes; one patient was found to have the Carney-Stratakis syndrome (CSS), and his PGL was discovered during surgery for gastrointestinal stromal tumor. Our results show that SDHx mutations are prevalent in pediatric and adult PGLs of the organ of Zuckerkandl. Patients with PGLs of the organ of Zuckerkandl should be screened for SDHx mutations and the CSS; in addition, asymptomatic carriers of an SDHx mutation among the relatives of affected patients may benefit from tumor screening for early PGL detection.

Tumor risks and genotype-phenotype-proteotype analysis in 358 patients with germline mutations in SDHB and SDHD

Succinate dehydrogenase B (SDHB) and D (SDHD) subunit gene mutations predispose to adrenal and extraadrenal pheochromocytomas, head and neck paragangliomas (HNPGL), and other tumor types. We report tumor risks in 358 patients with SDHB (n=295) and SDHD (n=63) mutations. Risks of HNPGL and pheochromocytoma in SDHB mutation carriers were 29% and 52%, respectively, at age 60 years and 71% and 29%, respectively, in SDHD mutation carriers. Risks of malignant pheochromocytoma and renal tumors (14% at age 70 years) were higher in SDHB mutation carriers; 55 different mutations (including a novel recurrent exon 1 deletion) were identified. No clear genotype-phenotype correlations were detected for SDHB mutations. However, SDHD mutations predicted to result in loss of expression or a truncated or unstable protein were associated with a significantly increased risk of pheochromocytoma compared to missense mutations that were not predicted to impair protein stability (most such cases had the common p.Pro81Leu mutation). Analysis of the largest cohort of SDHB/D mutation carriers has enhanced estimates of penetrance and tumor risk and supports in silicon protein structure prediction analysis for functional assessment of mutations. The differing effect of the SDHD p.Pro81Leu on HNPGL and pheochromocytoma risks suggests differing mechanisms of tumorigenesis in SDH-associated HNPGL and pheochromocytoma.

Mutations of the metabolic genes IDH1, IDH2, and SDHAF2 are not major determinants of the pseudohypoxic phenotype of sporadic pheochromocytomas and paragangliomas

CONTEXT

Pheochromocytomas and paragangliomas are genetically heterogeneous tumors of neural crest origin. Approximately half of these tumors activate a pseudohypoxic transcription response, which is due in a minority of the cases to germline mutations of the VHL gene or the genes encoding subunits of the metabolic enzyme succinate dehydrogenase (SDH), SDHB, SDHC, or SDHD. However, the genetic basis of the hypoxic-like profile of the remaining tumors is undetermined. Mutations in genes involved in the energy metabolism, isocitrate dehydrogenase 1 (IDH1) and -2 (IDH2) and SDHAF2, a component of SDH, can mimic a pseudohypoxic state.

DESIGN

We examined the sequence spanning the mutation-susceptible codons 132 of IDH1 and 172 of IDH2, and the entire coding region of SDHAF2, in 104 pheochromocytomas and paragangliomas, including tumors with a pseudohypoxic expression profile.

RESULTS

We did not find mutations in IDH1, IDH2, or SDHAF2 in any of the tumors in this cohort.

CONCLUSION

Conserved residues of IDH1 and IDH2 or the SDHAF2 gene are not frequently mutated in pheochromocytomas and paragangliomas. The molecular basis for activation of a hypoxic response in the majority of tumors without VHL or SDH mutations remains to be defined.

Mutation analysis of the SDHB and SDHD genes in pheochromocytomas and paragangliomas: identification of a novel nonsense mutation (Q168X) in the SDHB gene

Pheochromocytoma (PCC) and paraganglioma (PGL) are tumors of the autonomic nervous system. The former is a tumor that occurs in only adrenal glands, and the latter can be found in the head and neck or in the thorax and abdomen. In PCC and PGL, genetic mutations account for approximately 30% of functional (secrete catecholamines) and nonfunctional cases. In addition to RET, VHL and NF-1, genes encoding succinate dehydrogenase complex subunit B (SDHB), subunit C (SDHC), and subunit D (SDHD) are recognized as susceptibility genes for PCC and PGL. Recently, PCC and PGL caused by genetic mutations of SDHB, SDHC and SDHD were established as hereditary pheochromocytoma paraganglioma syndrome (HPPS). Approximately 15% of all PCCs and PGLs are recognized as HPPS. Among these three susceptibility genes, SDHB and SDHD are known to be strongly related to HPPS. The aim of this study was to analyze SDHB and SDHD mutations in PCC and PGL patients. Among 18 patients, we identified a novel heterozygous nonsense mutation at codon 168 resulting in a CAG (glutamine) to TAG (stop) substitution (Q168X) in the SDHB gene in a patient diagnosed with solitary sporadic PGL. A number of studies have reported that SDHB mutation-associated disease demonstrates a higher rate of malignancy. However, all seven patients diagnosed with malignancy in this study did not have genetic mutation of SDHB and only one patient with no malignant sign had genetic mutation of SDHB. Further accumulation of cases is necessary to confirm the association between SDHB mutation and malignant potential.

Phaeochromocytomas and sympathetic paragangliomas

BACKGROUND

About 24 per cent of phaeochromocytomas (PCCs) and sympathetic paragangliomas (sPGLs) appear in familial cancer syndromes, including multiple endocrine neoplasia type 2, von Hippel-Lindau disease, neurofibromatosis type 1 and PCC-paraganglioma syndrome. Identification of these syndromes is of prime importance for patients and their relatives. Surgical resection is the treatment of choice for both PCC and sPGL, but controversy exists about the management of patients with bilateral or multiple tumours.

METHODS

Relevant medical literature from PubMed, Ovid and Embase websites until 2009 was reviewed for articles on PCC, sPGL, hereditary syndromes and their treatment.

DISCUSSION

Genetic testing for these syndromes should become routine clinical practice for those with PCC or sPGL. Patients should be referred to a clinical geneticist. Patients and family members with proven mutations should be entered into a standardized screening protocol. The preferred treatment of PCC and PGL is surgical resection; to avoid the lifelong consequences of bilateral adrenalectomy, cortex-sparing adrenalectomy is the treatment of choice.

R27X nonsense mutation of the SDHB gene in a patient with sporadic malignant paraganglioma

It has been estimated that approximately 10% of pheochromocytomas and paragangliomas are part of a hereditary syndrome. Recent studies, however, suggest that the genetic involvement in pheochromocytoma/paraganglioma is actually far more common. Here, we report a case of malignant paraganglioma with no apparent family history. A 59-year-old man was referred to our services because of multiple abdominal masses. Plasma and urine adrenalin and noradrenalin levels were slightly elevated, and plasma dopamine and urine vanillylmandelic acid levels were remarkably elevated. Abdominal and chest computed tomography revealed multiple masses in the para-aortic region and in both lungs. Although (131)I-meta iodobenzylguanidine scintigraphy did not show significant uptake in these tumors, a 6-[(18)F]fluorodeoxyglucose positron emission tomographic scanning study showed multiple areas of uptake corresponding to the tumors. Biopsy of the tumors revealed paraganglioma with chromogranin A-immunopositive cells. Genetic analysis indicated a nonsense mutation at codon 27 of the SDHB gene. As recently described, SDHB mutations may cause extra-adrenal and malignant paragangliomas, such as in the present case.

Loss of heterozygosity of succinate dehydrogenase B mutation by direct sequencing in synchronous paragangliomas

Extraadrenal pheochromocytomas and paragangliomas are rare entities within the pediatric population. We report the presentation of three synchronous extra-adrenal abdominal paragangliomas in an adolescent boy who carries a germline mutation in the succinate dehydrogenase B (SDHB) gene. Loss of heterozygosity of this allele was demonstrated by direct sequencing of DNA from two of his tumors, confirming loss of tumor suppressor function in the pathogenesis of these paragangliomas.

Penetrance and clinical consequences of a gross SDHB deletion in a large family

Mutations in the gene encoding subunit B of the mitochondrial enzyme succinate dehydrogenase (SDHB) are inherited in an autosomal dominant manner and are associated with hereditary paraganglioma (PGL) and pheochromocytoma. The phenotype of patients with SDHB point mutations has been previously described. However, the phenotype and penetrance of gross SDHB deletions have not been well characterized as they are rarely described. The objective was to describe the phenotype and estimate the penetrance of an exon 1 large SDHB deletion in one kindred. A retrospective and prospective study of 41 relatives across five generations was carried out. The main outcome measures were genetic testing, clinical presentations, plasma catecholamines and their O-methylated metabolites. Of the 41 mutation carriers identified, 11 were diagnosed with PGL, 12 were found to be healthy carriers after evaluation, and 18 were reportedly healthy based on family history accounts. The penetrance of PGL related to the exon 1 large SDHB deletion in this family was estimated to be 35% by age 40. Variable expressivity of the phenotype associated with a large exon 1 SDHB deletion was observed, including low penetrance, diverse primary PGL tumor locations, and malignant potential.

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.

Ischemic stroke and rhabdomyolysis in a 15-year-old girl with paraganglioma due to an SDHB exon 6 (Q214X) mutation

BACKGROUND

We report a 15-year-old girl with a recent diagnosis of type 2 diabetes mellitus who presented in malignant hypertensive crisis (BP 210/120 mm Hg). Abdominal CT showed an 8.2 x 4.7 x 7.0 cm mass in the region of the organ of Zuckerkandl. MIBG scan showed a single paraganglioma without metastatic foci. Plasma total metanephrines were 232,176.4 pmol/l [263-1052] with normetanephrine predominance. Pre-operative course was complicated by ischemic stroke in the left MCA and right thalamic regions, acute renal failure, rhabdomyolysis and congestive heart failure. She required massive doses of propranolol, phenoxybenzamine, doxazosin and metyrosine prior to surgery.

RESULTS

Pathology showed a Zellballen pattern, negative tumor margins and benign para-aortic lymph nodes. Mutation analysis of the succinate dehydrogenase type B (SDHB) gene revealed a heterozygous change of C to T at position 640 in exon 6 (Q214X) predicting an amino acid change to a stop codon.

CONCLUSION

We report a severe clinical phenotype in a patient with a paraganglioma affecting multiple organ systems, due to an SDHB mutation. SDHB mutation warrants close follow up and investigation of the family due to high malignant potential and risk of familial occurrence.

Similar gene expression profiles of sporadic, PGL2-, and SDHD-linked paragangliomas suggest a common pathway to tumorigenesis

Background

Paragangliomas of the head and neck are highly vascular and usually clinically benign tumors arising in the paraganglia of the autonomic nervous system. A significant number of cases (10–50%) are proven to be familial. Multiple genes encoding subunits of the mitochondrial succinate-dehydrogenase (SDH) complex are associated with hereditary paraganglioma: SDHB, SDHC and SDHD. Furthermore, a hereditary paraganglioma family has been identified with linkage to the PGL2 locus on 11q13. No SDH genes are known to be located in the 11q13 region, and the exact gene defect has not yet been identified in this family.

Methods

We have performed a RNA expression microarray study in sporadic, SDHD- and PGL2-linked head and neck paragangliomas in order to identify potential differences in gene expression leading to tumorigenesis in these genetically defined paraganglioma subgroups. We have focused our analysis on pathways and functional gene-groups that are known to be associated with SDH function and paraganglioma tumorigenesis, i.e. metabolism, hypoxia, and angiogenesis related pathways. We also evaluated gene clusters of interest on chromosome 11 (i.e. the PGL2 locus on 11q13 and the imprinted region 11p15).

Results

We found remarkable similarity in overall gene expression profiles of SDHD -linked, PGL2-linked and sporadic paraganglioma. The supervised analysis on pathways implicated in PGL tumor formation also did not reveal significant differences in gene expression between these paraganglioma subgroups. Moreover, we were not able to detect differences in gene-expression of chromosome 11 regions of interest (i.e. 11q23, 11q13, 11p15).

Conclusion

The similarity in gene-expression profiles suggests that PGL2, like SDHD, is involved in the functionality of the SDH complex, and that tumor formation in these subgroups involves the same pathways as in SDH linked paragangliomas. We were not able to clarify the exact identity of PGL2 on 11q13. The lack of differential gene-expression of chromosome 11 genes might indicate that chromosome 11 loss, as demonstrated in SDHD-linked paragangliomas, is an important feature in the formation of paragangliomas regardless of their genetic background.

Impact of screening kindreds for SDHD p.Cys11X as a common mutation associated with paraganglioma syndrome type 1

CONTEXT AND OBJECTIVE

Germline mutations of the genes SDHB, SDHC, and SDHD predispose to paraganglioma syndromes. Mutation-specific counseling, risk assessment, and management recommendations ideally should be performed. Here, we provide data for a single common mutation of the SDHD gene.

METHODS

The European-American Pheochromocytoma-Paraganglioma Registry served as the source for unrelated index cases affected by pheochromocytoma or paraganglioma. Patients with the SDHD c.33 C-->A (p.Cys11X) germline mutations were reinvestigated by whole-body magnetic resonance imaging and 24-h urinary catecholamine assay. First-degree relatives underwent genetic testing and those testing positive had same clinical investigations. Microsatellite analyses were used to test the hypothesis that all index cases were related and the mutation is a founding one.

RESULTS

Sixteen index cases with the mutation SDHD p.Cys11X are registered. After testing their relatives, there were a total of 25 mutation carriers. We excluded seven subjects who inherited the mutation from the mother because of maternal imprinting. Thus, 18 mutation carriers were clinically affected. Among these 16 (89%) had head and neck paragangliomas, six (33%) thoracic tumors, six (33%) extraadrenal retroperitoneal, and five (28%) intraadrenal. Of note, 16 (89%) had multiple tumors at first diagnosis, and one (5%) had signs of malignancy during follow-up. Overall penetrance was 100% at age 54. Haplotype analyses revealed evidence for a founder effect.

CONCLUSIONS

The SDHD p.Cys11X mutation is a founding mutation associated with a high penetrance for paraganglial tumors of the skull base, neck, thorax, and retroperitoneum in the first four decades of life and, rarely, with malignancy.

Clinical manifestations of familial paraganglioma and phaeochromocytomas in succinate dehydrogenase B (SDH-B) gene mutation carriers

OBJECTIVE

Phaeochromocytomas and paragangliomas are familial in up to 25% of cases and can result from succinate dehydrogenase (SDH) gene mutations. The aim of this study was to describe the clinical manifestations of subjects with SDH-B gene mutations.

DESIGN

Retrospective case-series.

PATIENTS

Thirty-two subjects with SDH-B gene mutations followed up between 1975 and 2007. Mean follow-up of 5.8 years (SD 7.4, range 0-31). Patients seen at St Bartholomew's Hospital, London and other UK centres.

MEASUREMENTS

Features of clinical presentation, genetic mutations, tumour location, catecholamine secretion, clinical course and management.

RESULTS

Sixteen of 32 subjects (50%) were affected by disease. Two previously undescribed mutations in the SDH-B gene were noted. A family history of disease was apparent in only 18% of index subjects. Mean age at diagnosis was 34 years (SD 15.4, range 10-62). 50% of affected subjects had disease by the age of 26 years. 69% (11 of 16) were hypertensive and 80% (12 of 15) had elevated secretions of catecholamines/metabolites. 24% (6 of 25) of tumours were located in the adrenal and 76% (19 of 25) were extra-adrenal. 19% (3 of 16) had multifocal disease. Metastatic paragangliomas developed in 31% (5 of 16). One subject developed a metastatic type II papillary renal cell carcinoma. The cohort malignancy rate was 19% (6 of 32). Macrovascular disease was noted in two subjects without hypertension.

CONCLUSION

SDH-B mutation carriers develop disease early and predominantly in extra-adrenal locations. Disease penetrance is incomplete. Metastatic disease is prominent but levels are less than previously reported. Clinical manifestations may include papillary renal cell carcinoma and macrovascular disease.

Evaluation of a functional epigenetic approach to identify promoter region methylation in phaeochromocytoma and neuroblastoma

The molecular genetics of inherited phaeochromocytoma have received considerable attention, but the somatic genetic and epigenetic events that characterise tumourigenesis in sporadic phaeochromocytomas are less well defined. Previously, we found considerable overlap between patterns of promoter region tumour suppressor gene (TSG) hypermethylation in two neural crest tumours, neuroblastoma and phaeochromocytoma. In order to identify candidate biomarkers and epigenetically inactivated TSGs in phaeochromocytoma and neuroblastoma, we characterised changes in gene expression in three neuroblastoma cell lines after treatment with the demethylating agent 5-azacytidine. Promoter region methylation status was then determined for 28 genes that demonstrated increased expression after demethylation. Three genes HSP47, homeobox A9 (HOXA9) and opioid binding protein (OPCML) were methylated in >10% of phaeochromocytomas (52, 17 and 12% respectively). Two of the genes, epithelial membrane protein 3 (EMP3) and HSP47, demonstrated significantly more frequent methylation in neuroblastoma than phaeochromocytoma. These findings extend epigenotype of phaeochromocytoma and identify candidate genes implicated in sporadic phaeochromocytoma tumourigenesis.