Novel mutations and the emergence of a common mutation in the SDHD gene causing familial paraganglioma

Crystallographic investigation of the ubiquinone binding site of respiratory Complex II and its inhibitors

The quinone binding site (Q-site) of Mitochondrial Complex II (succinate-ubiquinone oxidoreductase) is the target for a number of inhibitors useful for elucidating the mechanism of the enzyme. Some of these have been developed as fungicides or pesticides, and species-specific Q-site inhibitors may be useful against human pathogens. We report structures of chicken Complex II with six different Q-site inhibitors bound, at resolutions 2.0-2.4 Å. These structures show the common interactions between the inhibitors and their binding site. In every case a carbonyl or hydroxyl oxygen of the inhibitor is H-bonded to Tyr58 in subunit SdhD and Trp173 in subunit SdhB. Two of the inhibitors H-bond Ser39 in subunit SdhC directly, while two others do so via a water molecule. There is a distinct cavity that accepts the 2-substituent of the carboxylate ring in flutolanil and related inhibitors. A hydrophobic "tail pocket" opens to receive a side-chain of intermediate-length inhibitors. Shorter inhibitors fit entirely within the main binding cleft, while the long hydrophobic side chains of ferulenol and atpenin A5 protrude out of the cleft into the bulk lipid region, as presumably does that of ubiquinone. Comparison of mitochondrial and Escherichia coli Complex II shows a rotation of the membrane-anchor subunits by 7° relative to the iron‑sulfur protein. This rotation alters the geometry of the Q-site and the H-bonding pattern of SdhB:His216 and SdhD:Asp57. This conformational difference, rather than any active-site mutation, may be responsible for the different inhibitor sensitivity of the bacterial enzyme.

Recurrence and Progression of Head and Neck Paragangliomas after Treatment

OBJECTIVE

To characterize the recurrence of head and neck paragangliomas and the factors associated with disease progression after treatment.

STUDY DESIGN

Retrospective cohort study.

SETTING

Tertiary care center.

SUBJECTS AND METHODS

In total, 173 adults with 189 paragangliomas (41.3% carotid body, 29.1% glomus jugulare, 19.0% glomus tympanicum, and 10.6% glomus vagale) treated between 1990 and 2010 were evaluated to determine the incidence and risk of recurrence using Cox proportional hazards.

RESULTS

The mean (SD) follow-up duration was 8.6 (9.1) years. The incidence was 2.92 recurrences per 100 person-years. The rate of recurrence was 8.2% (95% confidence interval [CI], 3.7-12.7) after 4 years and 17.1% (95% CI, 10.2-24.0) after 10 years. Glomus jugulare tumors were more likely to recur (hazard ratio [HR], 3.69; 95% CI, 1.70-8.01; P < .001) while carotid body tumors were less likely (HR, 0.44; 95% CI, 0.21-0.97; P = .041). Radiation had a lower risk of recurrence or progression compared to surgical excision (HR, 0.30; 95% CI, 0.10-.94; P = .040). Recurrence was associated with right-sided paragangliomas (HR, 3.60; 95% CI, 1.63-7.75; P = .001). The median time to recurrence was 18.4 years. Six (3.2%) patients developed metastasis, which was more common with local recurrence (9.5% vs 1.4%, P = .015).

CONCLUSIONS

Recurrence is more common with glomus jugulare tumors and less common with carotid body tumors. Radiation may have a lower risk of recurrence or progression than surgery for some paraganglioma types. Metastasis is rare but more likely with recurrent disease. Surveillance neck imaging is recommended every several years for decades after treatment.

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.

New HIF2α inhibitors: potential implications as therapeutics for advanced pheochromocytomas and paragangliomas

Two recent independent studies published in Nature show robust responses of clear cell renal cell carcinoma (ccRCC) cell lines, preclinical ccRCC xenograft models and, remarkably, a patient with progressive ccRCC despite receiving multiple lines of treatment, to the long-awaited, recently developed inhibitors of hypoxia-inducible factor 2-alpha (HIF2α). This commentary published in Endocrine-Related Cancer is based on the recognition of similar molecular drivers in ccRCC and the endocrine neoplasias pheochromocytomas and paragangliomas (PPGLs), ultimately leading to stabilization of HIFs. HIF-stabilizing mutations have been detected in the von Hippel-Lindau (VHL) gene, as well as in other genes, such as succinate dehydrogenase (SDHx), fumarate hydratase (FH) and transcription elongation factor B subunit 1 (TCEB1), as well as the gene that encodes HIF2α itself: EPAS1^HIF2α Importantly, the recent discovery of EPAS1 mutations in PPGLs and the results of comprehensive in vitro and in vivo studies revealing their oncogenic roles characterized a hitherto unknown direct mechanism of HIF2α activation in human cancer. The now available therapeutic opportunity to successfully inhibit HIF2α pharmacologically with PT2385 and PT2399 will certainly spearhead a series of investigations in several types of cancers, including patients with SDHB-related metastatic PPGL for whom limited therapeutic options are currently available. Future studies will determine the efficacy of these promising drugs against the hotspot EPAS1 mutations affecting HIF2α amino acids 529-532 (in PPGLs) and amino acids 533-540 (in erythrocytosis type 4), as well as against HIF2α protein activated by VHL, SDHx and FH mutations in PPGL-derived chromatin cells.

Neuroendocrine Tumors of the Urinary Bladder According to the 2016 World Health Organization Classification: Molecular and Clinical Characteristics

Neuroendocrine neoplasms of the urinary bladder are a rare type of tumor that account for a small percentage of urinary bladder neoplasms. These tumors of the urinary bladder range from well-differentiated neuroendocrine neoplasms (carcinoids) to the more aggressive subtypes such as small cell carcinoma. Despite the rarity of the neuroendocrine tumors of the bladder, there has been substantial investigation into the underlying genomic, molecular, and the cellular alterations within this group of neoplasms. Accordingly, these findings are increasingly incorporated into the understanding of clinical aspects of these neoplasms. In this review, we provide an overview of recent literature related to the 2016 World Health Organization Classification of Neuroendocrine Tumors of the Urinary Bladder. Particular emphasis is placed on molecular alterations and recently described gene expression. The neuroendocrine tumors of the urinary bladder are subdivided into four subtypes. Similar to their pulmonary and other extrapulmonary site counterparts, these have different degrees of neuroendocrine differentiation and morphological features. The clinical aspects of four subtypes of neuroendocrine tumor are discussed with emphasis of the most recent developments in diagnosis, treatment, and prognosis. An understanding of molecular basis of neuroendocrine tumors will provide a base of knowledge for future investigations into this group of unusual bladder neoplasms.

Identification of eight novel SDHB, SDHC, SDHD germline variants in Danish pheochromocytoma/paraganglioma patients

Background

Germline mutations in the succinate dehydrogenase complex genes SDHB, SDHC, and SDHD predispose to pheochromocytomas and paragangliomas. Here, we examine the SDHB, SDHC, and SDHD mutation spectrum in the Danish population by screening of 143 Danish pheochromocytoma and paraganglioma patients.

Methods

Mutational screening was performed by Sanger sequencing or next-generation sequencing. The frequencies of variants of unknown clinical significance, e.g. intronic, missense, and synonymous variants, were determined using the Exome Aggregation Consortium database, while the significance of missense mutations was predicted by in silico and loss of heterozygosity analysis when possible.

Results

We report 18 germline variants; nine in SDHB, six in SDHC, and three in SDHD. Of these 18 variants, eight are novel. We classify 12 variants as likely pathogenic/pathogenic, one as likely benign, and five as variants of unknown clinical significance.

Conclusions

Identifying and classifying SDHB, SDHC, and SDHD variants present in the Danish population will augment the growing knowledge on variants in these genes and may support future clinical risk assessments.

Structural basis for malfunction in complex II

Complex II couples oxidoreduction of succinate and fumarate at one active site with that of quinol/quinone at a second distinct active site over 40 Å away. This process links the Krebs cycle to oxidative phosphorylation and ATP synthesis. The pathogenic mutation or inhibition of human complex II or its assembly factors is often associated with neurodegeneration or tumor formation in tissues derived from the neural crest. This brief overview of complex II correlates the clinical presentations of a large number of symptom-associated alterations in human complex II activity and assembly with the biochemical manifestations of similar alterations in the complex II homologs from Escherichia coli. These analyses provide clues to the molecular basis for diseases associated with aberrant complex II function.

Genetic and clinical characteristics of head and neck paragangliomas in a Chinese population

OBJECTIVES/HYPOTHESIS

Head and neck paragangliomas (PGLs) are rare and frequently associated with germline mutations of the succinate dehydrogenase (SDH) genes, especially for familial cases. The purpose of the study was to explore genetic and clinical characteristics of head and neck PGLs in a Chinese population.

STUDY DESIGN

Retrospective review.

METHODS

One hundred thirty-two patients who had undergone resection for head and neck PGLs between 1975 and 2010 were identified. Clinical characteristics and outcomes were reviewed. Analysis of the SDH genes was performed in 29 patients and one kindred with familial PGL to identify germline mutations in the SDHB, SDHC, and SDHD genes by direct DNA sequencing.

RESULTS

There were 69 male (52.3%) and 63 female (47.76%) patients, with a mean age of 43.6 years (range, 13-72 years). Most lesions (61.4%) were PGLs of the carotid bifurcation. Others included jugular (25.0%), vagal (9.1%), and tympanic PGLs. Twenty-one patients (15.9%) had multiple PGLs, 25 patients (18.9%) had a malignant PGL, and 15 patients (11.4%) in four families were familial PGLs. Analysis of the SDH genes in 29 patients showed that four familial cases (including two patients) carried a heterozygotic missense mutation in SDHD. The mutation was W43X, located in SDHD-exon 2. Four sporadic cases carried samesense germline mutations in SDHB-exon 1, and they were all malignant PGLs.

CONCLUSIONS

Multifocal occurrence, potential malignancy, and genetic aspect should be considered in patients with head and neck PGLs. The high frequency of founder mutations in SDHB suggests a higher prevalence of malignancy, and the SDHD mutation is usually associated with familial cases.

The endemic paraganglioma syndrome type 1: origin, spread, and clinical expression

CONTEXT

Anecdotal evidence suggests a high incidence in Trentino, Italy, of head and neck paragangliomas (HNPGL), a rare autosomal dominant disease called paraganglioma type 1 syndrome and caused by germ-line mutations of the SDHD gene.

OBJECTIVE

The aim of this study was to investigate the origin, spread, and clinical expression of the disease in this geographic region.

DESIGN, SETTING, AND PARTICIPANTS

Trentino natives with HNPGL were recruited for establishing clinical expression of the disease, presence of a founder effect, and age of common ancestor. A large sample of the local population was recruited for determination of mutation prevalence and spread.

MAIN OUTCOME MEASURES

SDHD genetic testing was offered to first-degree relatives, and clinical surveillance was offered to at-risk carriers. The hypothesis of a founder effect was explored by haplotype analysis, and time to the most recent common ancestor was estimated by decay of haplotype sharing over time.

RESULTS

A total of 287 of the 540 recruited individuals from 95 kindreds carried the SDHD c.341A>G p.Tyr114Cys mutation. The prevalent phenotype was bilateral or multiple HNPGL, with low prevalence of pheochromocytoma and malignant forms. Penetrance was high. A common ancestor was dated between the 14th and 15th century, with the mutation spreading from the Mocheni Valley, a geographic, cultural and, presumably, a genetic isolate to 1.5% of the region's population.

CONCLUSIONS

A combination of particular demographic, geographical, and historical conditions has resulted in the oldest and largest SDHD founder effect so far characterized and has transformed a rare disease into an endemic disease with major public health implications.

Head and neck paragangliomas: Report of 175 patients (1989-2010)

BACKGROUND

Attention of the otorhinolaryngologist needs to be drawn to the versatile aspects of head and neck paragangliomas (PGLs).

METHODS

This study is a retrospective, nonrandomized clinical study of all 175 individuals with PGLs treated in our department between 1989 and 2010. A genetic analysis was performed on 86 patients.

RESULTS

The 175 patients presented 224 head and neck PGLs as well as 2 thyroid papillary carcinomas. Genetic analysis resulted in 1 patient positive for a von Hippel-Lindau (VHL) gene mutation and 34 for succinate dehydrogenase (SDH) gene mutations (22 SDHD, 7 SDHC, and 5 SDHB), 12 of the latter carrying a novel mutation. Thirty-three patients (18.9%) had multiple PGLs and 11 patients (6.3%) had a malignant paraganglioma. SDH-mutation carriers had multiple tumors in 64.7% and malignant paragangliomas in 20.6%.

CONCLUSIONS

Multifocal occurrence, potential malignancy, genetic aspects, possible coincidence of thyroid carcinoma, and hormone production have to be considered in patients with head and neck PGLs.

Clinical, histopathologic, and radiographic indicators of malignancy in head and neck paragangliomas

OBJECTIVE: The goal of this study is to review our series of head and neck paragangliomas to identify factors that may help in predicting malignancy.

STUDY DESIGN: Case series with chart review.

SETTING: Academic medical center.

SUBJECTS AND METHODS: Subjects with head and neck paragangliomas at our institution from 1976 to current were reviewed. In addition to statistical comparisons of epidemiologic factors, pathologic and radiographic characteristics were reviewed.

RESULTS: Of the 84 subjects, there were seven malignant paragangliomas (8%). Age was found to be significantly different between the benign and malignant subgroups, with an average age of 54 ± 16 and 40 ± 12 years, respectively ( P = 0.02). Pain was a presenting complaint in five patients with benign disease (6%), and five of the seven malignant patients (71%) presented with pain, showing a significant association between pain and disease type ( P <0.0001). The odds ratio for a patient with pain having a malignant tumor was 36 (95% CI: 5.5–234). Enlarging neck mass was noted in all cases of malignant disease, but only in 31 percent of cases of benign disease ( P < 0.0001). In a secondary analysis of carotid body tumors alone, enlarging neck mass was not found to be significant between benign and malignant disease ( P = 0.14). However, pain continued to be significantly different, with 67 percent of malignant lesions demonstrating pain, compared with only 11 percent of benign lesions ( P = 0.01). CONCLUSION: This study suggests that pain, a rapidly enlarging neck mass, and younger age are predictive factors of underlying malignancy, which should prompt one to consider an aggressive diagnostic and management approach.

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.

High prevalence of SDHB mutations in head and neck paraganglioma in Belgium

BACKGROUND

Recent reports have found genetic mutations in up to one quarter of patients harbouring pheochromocytoma and/or paraganglioma. This high prevalence was mainly due to the discovery of the role of SDH genes. While SDHD has been more frequently associated with the pathogenesis of head and neck paragangliomas, SDHB mutations were mainly associated with malignant and/or extra-adrenal pheochromocytoma/paraganglioma.

OBJECTIVE

To look for mutations in susceptibility genes and genotype-phenotype correlations in patients with pheochromocytoma and/or paraganglioma from Belgium.

METHODS

Screening of the coding parts of SDH, VHL and RET genes was performed by SSCP in patients with pheochromocytoma and/or paraganglioma diagnosed at or referred to the Cliniques Universitaires Saint Luc from May 2003 to May 2006.

RESULTS

Fifty-six unrelated patients were included (36 head and neck paragangliomas, including six familial cases and 30 sporadic cases; 18 abdominal pheochromocytoma/paraganglioma and two paraganglioma of the cauda equina). The overall prevalence of mutations was 41% (n = 23 including 19 head and neck paragangliomas and four abdominal pheochromocytoma/paraganglioma), mainly due to SDH mutations. While SDHD mutations were found in all patients with familial head and neck paragangliomas, in sporadic cases, the prevalence of SDHB mutations (n = 8, 27%) was twice that of SDHD mutations (n = 4, 13%). Patients harbouring SDHB mutations had unilateral late-onset head and neck tumours without evidence of recurrence or malignancy.

CONCLUSION

This Belgian series confirms the elevated prevalence of predisposing mutations in patients with head and neck and extra-adrenal paragangliomas, but differs from previous reports by the high frequency of SDHB mutations associated with head and neck paragangliomas without evidence of recurrence or malignancy.

Systematic screening and treatment evaluation of hereditary neck paragangliomas

Familial paragangliomas of the neck are often bilateral and more aggressive than spontaneous forms. Tumors appear earlier (2nd-4th decade) often with diffuse, multifocal involvement. Without treatment, these tumors can lead to significant morbidity. Three families with succinate dehydrogenase subunit D (SDHD) germline mutations underwent clinical and genetic evaluation. Patients were screened using ultrasound and evaluated further with conventional and functional imaging. Tumors with a diameter >1.5 cm were surgically removed. Multicentric and bilateral tumors were detected in 9/13 (69%) and 8/13 (62%) patients, respectively. Surgical morbidity occurred in 64% of patients. Local recurrence was 57%, although this was lower in tumors with a diameter <2 cm. We recommend an algorithm for a systematic approach to the diagnosis, monitoring, and treatment of familial head and neck paragangliomas. Operative treatment in advanced stages often leads to unwanted morbidity, such that earlier detection and treatment of smaller tumors seems to be of benefit.

Ubiquinone-binding Site Mutations in the Saccharomyces cerevisiae Succinate Dehydrogenase Generate Superoxide and Lead to the Accumulation of Succinate

The mitochondrial succinate dehydrogenase (SDH) is an essential component of the electron transport chain and of the tricarboxylic acid cycle. Also known as complex II, this tetrameric enzyme catalyzes the oxidation of succinate to fumarate and reduces ubiquinone. Mutations in the human SDHB, SDHC, and SDHD genes are tumorigenic, leading to the development of several types of tumors, including paraganglioma and pheochromocytoma. The mechanisms linking SDH mutations to oncogenesis are still unclear. In this work, we used the yeast SDH to investigate the molecular and catalytic effects of tumorigenic or related mutations. We mutated Arg(47) of the Sdh3p subunit to Cys, Glu, and Lys and Asp(88) of the Sdh4p subunit to Asn, Glu, and Lys. Both Arg(47) and Asp(88) are conserved residues, and Arg(47) is a known site of cancer causing mutations in humans. All of the mutants examined have reduced ubiquinone reductase activities. The SDH3 R47K, SDH4 D88E, and SDH4 D88N mutants are sensitive to hyperoxia and paraquat and have elevated rates of superoxide production in vitro and in vivo. We also observed the accumulation and secretion of succinate. Succinate can inhibit prolyl hydroxylase enzymes, which initiate a proliferative response through the activation of hypoxia-inducible factor 1alpha. We suggest that SDH mutations can promote tumor formation by contributing to both reactive oxygen species production and to a proliferative response normally induced by hypoxia via the accumulation of succinate.

Malignant paragangliomas associated with mutations in the succinate dehydrogenase D gene

INTRODUCTION

Malignant paragangliomas have been well described in carriers of mutations of the succinate dehydrogenase B (SDHB) gene, but have rarely been associated with mutations in the succinate dehydrogenase D (SDHD) gene.

AIM

The aim of the study was to report the different clinical expression patterns of malignant paragangliomas in five patients with SDHD (D92Y) mutations observed in approximately 200 SDHD (D92Y) mutation carriers followed in our institution.

RESULTS

Metastasis and/or local tumor invasion was documented 0 (n=2), 1, 18, and 30 yr after the initial diagnosis of paraganglioma. Malignancy was proven by paraganglioma bone metastases (n=2), intrathoracic paraganglioma with lymph node metastases, locally invasive head-and-neck paraganglioma with destruction of the petrosal bone, and locally invasive paraganglioma of the bladder with lymph node metastases. Four of the five patients developed catecholamine excess during follow-up due to intraadrenal paraganglioma (pheochromocytoma) (n=1), extra adrenal paraganglioma (n=2), and presumed subclinical disease (n=1).

CONCLUSION

SDHD mutations (D92Y) are associated with malignant paragangliomas and catecholamine excess with remarkable interindividual variations despite the same mutation. We estimate that the prevalence of malignancy in carriers of D92Y mutations is at least 2.5%.

Paraganglioma syndrome: SDHB, SDHC, and SDHD mutations in head and neck paragangliomas

Paraganglioma syndrome includes head and neck paraganglioma and pheochromocytoma, and is classified according to the three susceptibility genes involved, SDHB, SDHC, and SDHD. This study assessed the prevalence of germline mutations in SDHB, SDHC, and SDHD genes in a consecutive population admitted to Padova Hospital consisting of 20 patients with head and neck paraganglioma (HNP). Mutations were identified in the three genes in four affected individuals, three sporadic cases and one with family history of HNP. The novel SDHB p.R242C mutation was identified in a sporadic monolateral carotid body tumor. The SDHC p.Q147X mutation, the first to be described in Italy, was detected in a sporadic monolateral jugulotympanic paraganglioma. The SDHD p.Y114C mutation was identified in two unrelated patients, one familial case of bilateral carotid body tumor and one multiple paraganglioma. SDHB, SDHC, and SDHD molecular screening is important in all HNPs, with or without primary indicators of paraganglioma syndrome, to orient mutation-driven clinical screening for additional HNPs and pheochromocytoma.

The role of Sdh4p Tyr-89 in ubiquinone reduction by the Saccharomyces cerevisiae succinate dehydrogenase

Succinate dehydrogenase (complex II or succinate:ubiquinone oxidoreductase) is a tetrameric, membrane-bound enzyme that catalyzes the oxidation of succinate and the reduction of ubiquinone in the mitochondrial respiratory chain. Two electrons from succinate are transferred one at a time through a flavin cofactor and a chain of iron-sulfur clusters to reduce ubiquinone to an ubisemiquinone intermediate and to ubiquinol. Residues that form the proximal quinone-binding site (Q(P)) must recognize ubiquinone, stabilize the ubisemiquinone intermediate, and protonate the ubiquinone to ubiquinol, while minimizing the production of reactive oxygen species. We have investigated the role of the yeast Sdh4p Tyr-89, which forms a hydrogen bond with ubiquinone in the Q(P) site. This tyrosine residue is conserved in all succinate:ubiquinone oxidoreductases studied to date. In the human SDH, mutation of this tyrosine to cysteine results in paraganglioma, tumors of the parasympathetic ganglia in the head and neck. We demonstrate that Tyr-89 is essential for ubiquinone reductase activity and that mutation of Tyr-89 to other residues does not increase the production of reactive oxygen species. Our results support a role for Tyr-89 in the protonation of ubiquinone and argue that the generation of reactive oxygen species is not causative of tumor formation.

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.

Genetic basis of phaeochromocytoma and paraganglioma

Advances in the knowledge of the genetics of phaeochromocytoma have broadened our understanding about the mechanisms of tumorigenesis. Formerly it was believed that 10% of phaeochromocytomas were associated with familial cancer syndromes, but it is now recognised that up to 30% of these tumours may be familial. In particular, attention has been focused on those patients with apparently sporadic presentations where 12-24% of patients have been shown to carry germline mutations indicating hereditary disease. Consideration of genetic testing is now recommended for all apparently sporadic cases and, following the identification of a mutation-positive carrier, the offering of genetic testing to first degree relatives. There is a need for lifelong follow up of affected individuals and asymptomatic mutation-positive carriers, but validation of screening protocols has yet to be determined.

Review: Should patients with apparently sporadic pheochromocytomas or paragangliomas be screened for hereditary syndromes?

CONTEXT

The recent identification of germline mutations of the mitochondrial complex II genes in variants of paraganglioma/pheochromocytoma syndrome has enlarged the number of known causative genes for hereditary pheochromocytoma. A question confronting clinicians is whether they should screen patients with apparently sporadic pheochromocytomas for unsuspected germline mutations of some or all of the seven genes known to cause hereditary paraganglioma or pheochromocytoma (NF1, VHL, RET, MEN1, SDHD, SDHC, and SDHB). A positive answer was suggested by a report that placed the estimate of hereditary disease in apparently sporadic pheochromocytoma as high as 24%.

EVIDENCE ACQUISITION

We applied clinically useful criteria to a review of the literature, defining cases of apparently sporadic pheochromocytoma as those without a suspicious personal or family history, with a focal, unilateral pheochromocytoma, and presenting at age less than 50 yr.

EVIDENCE SYNTHESIS

We reduced the overall estimate of unsuspected hereditary pheochromocytoma patients with apparently sporadic pheochromocytoma to approximately 17%. Mutations in only three genes (VHL, SDHB, and SDHD) accounted for almost this entire minority, and unsuspected RET mutation was rare. Costs, coverage by insurance, the potential effect on insurability, and deficient information for populations outside of referral centers should be considered before recommending genetic testing in patients with apparently sporadic presentations of pheochromocytomas.

CONCLUSION

We recommend genetic testing for patients with an apparently sporadic pheochromocytoma under the age of 20 yr with family history or features suggestive of hereditary pheochromocytoma or for patients with sympathetic paragangliomas. For individuals who do not meet these criteria, genetic testing is optional.

SDH Mutations in Patients Affected by Paraganglioma Syndromes: A Personal Experience

Mutations in genes encoding mitochondrial succinate dehydrogenase (SDH) are frequently involved in the development of neural crest-derived (NCD) tumors, such as pheochromocytomas (PHEOs) or paragangliomas (PGLs). In this study we report the results of sequencing analysis in leukocyte DNA of patients affected by PHEO/PGL who turned out to be SDH mutation carriers. A nonsense germline heterozygous mutation (Q109X) was found in the exon 4 of the SDHD gene in the index cases of six unrelated families affected by PHEO/PGL. Haplotype analysis showed the presence of a founder effect. Affected patients showed high clinical variability, ranging from monolateral to bilateral glomus tumors, variably associated or not with PGLs or PHEOs. A novel missense SDHD variant, T112I, was also found in one of our families. A new missense G106D mutation, involving a highly conserved amino acid, was found in two sisters affected by bilateral glomus tumors. A P81L mutation associated with abdominal and head and neck PGL was detected in three families. A G12S variant of the SDHD gene was found in one patient affected by a PHEO. The finding of this variant in 3 of 100 control subjects suggests that it is a polymorphism and not a mutation. A novel IVS2-1G>T variant was found at intron 2 of SDHD gene in one patient affected by a glomus tumor. All the tumors associated with SDHD mutations were benign. Conversely, the only mutation we found in SDHB gene (IVS3+1G>A) was associated with a malignant PHEO.

Genetic testing for pheochromocytoma-associated syndromes

Pheochromocytoma and paraganglioma are tumors of the autonomic nervous system. Various syndromes have been found to be associated with the development of pheochromocytomas and paragangliomas: multiple endocrine neoplasia type 2 (MEN 2, susceptibility gene: RET), von Hippel-Lindau disease (VHL, susceptibility gene: VHL), neurofibromatosis 1 (NF 1), and paraganglioma syndromes type 1, 3, and 4 (susceptibility genes: succinate dehydrogenase gene, SDH, subunits D, C and B, respectively). Prevalence and clinical features of pheochromocytomas and paragangliomas are different for each of these syndromes. Mutational analysis of the susceptibility genes of these syndromes in patients presenting with pheochromocytoma or paraganglioma may help to judge the risks of multifocality of the tumor as well as development of malignant pheochromocytoma or of other malignant tumors. Here we review the recent progress in clinical characterization and genetic testing for these syndromes. Based on tumor characteristics and prevalence data we give recommendations for an efficient genetic testing procedure in patients presenting with pheochromocytomas and paragangliomas.

Mutation analysis of the SDHD gene in four kindreds with familial paraganglioma: description of one novel germline mutation

The familial paraganglioma syndrome is an autosomal dominant disorder characterized by the presence of carotid body paragangliomas and, less frequently, paragangliomas of the glomus jugulare, glomus vagale, and adrenal pheochromocytomas. Germline mutations of the genes for succinate dehydrogenase subunits D, B, or C (SDHD, SDHB, SDHC) have been identified in some kindreds with familial paraganglioma. In this study, we report the clinicopathologic features of four different kindreds with familial paraganglioma, which were screened for germline mutations in the SDHD gene. DNA was obtained from tumor and normal tissue, as well as from peripheral blood. Mutation analysis was performed by single-strand conformation polymorphism analysis and DNA sequencing. SDHD germline mutations were detected in the affected family members of the four families, as well as in several asymptomatic carriers. An identical mutation in exon 4 of SDHD (334-337delACTG) was identified in two apparently unrelated kindreds. The third family showed a germline mutation in exon 2 (W43X). The mutations present in these three families had been previously described in Spanish families, suggesting a founder effect. The fourth family exhibited a mutation in exon 2 of SDHD (170-171delTT), which had not been previously identified. The affected family members of the four kindreds showed paragangliomas, located in the head and neck region, and all of them were benign. These results confirm that genetic testing of SDHD may be a powerful tool for the identification of the syndrome in patients with multiple or bilateral paragangliomas.

Crystal structure of mitochondrial respiratory membrane protein complex II

The mitochondrial respiratory Complex II or succinate:ubiquinone oxidoreductase (SQR) is an integral membrane protein complex in both the tricarboxylic acid cycle and aerobic respiration. Here we report the first crystal structure of Complex II from porcine heart at 2.4 A resolution and its complex structure with inhibitors 3-nitropropionate and 2-thenoyltrifluoroacetone (TTFA) at 3.5 A resolution. Complex II is comprised of two hydrophilic proteins, flavoprotein (Fp) and iron-sulfur protein (Ip), and two transmembrane proteins (CybL and CybS), as well as prosthetic groups required for electron transfer from succinate to ubiquinone. The structure correlates the protein environments around prosthetic groups with their unique midpoint redox potentials. Two ubiquinone binding sites are discussed and elucidated by TTFA binding. The Complex II structure provides a bona fide model for study of the mitochondrial respiratory system and human mitochondrial diseases related to mutations in this complex.

Pheochromocytoma and functional paraganglioma syndrome: no longer the 10% tumor

Pheochromocytomas and abdominal paragangliomas are catecholamine-producing tumors of the sympathetic nervous system, while head and neck paragangliomas are non-secreting tumors of parasympathetic origin. Recent developments in clinical and molecular research on these tumor forms have significantly clarified their genetic backgrounds and challenged the view of "pheochromocytoma as the 10% rule tumor." Firstly, a larger proportion of these tumors are today discovered in normotensive patients during imaging carried out for other reasons than suspicion of pheochromocytoma. Secondly, although the differential diagnosis between malignant and benign tumors remains a challenge, the risk of malignancy well exceeds the classical 10% in patients with extra-adrenal disease, and/or carriers of germ-line SDHB mutations. Finally, up to a third of patients carry a germ-line mutation in a gene predisposing to pheochromocytoma and/or paraganglioma. Identification of a constitutional mutation in RET, VHL, SDHD, or SDHB has implications for clinical screening and follow-up for both the patient and for relatives at risk who can be identified by screening for the same mutation. Genetic testing in apparently sporadic cases is therefore regarded as beneficial, especially in patients diagnosed before 50 years of age, and in patients with bilateral, multifocal, malignant and/or extra-adrenal disease.

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.

Role of VHL gene mutation in human cancer

Germline inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene causes the von Hippel-Lindau hereditary cancer syndrome, and somatic mutations of this gene have been linked to the development of sporadic hemangioblastomas and clear-cell renal carcinomas. The VHL tumor suppressor protein (pVHL), through its oxygen-dependent polyubiquitylation of hypoxia-inducible factor (HIF), plays a central role in the mammalian oxygen-sensing pathway. This interaction between pVHL and HIF is governed by post-translational prolyl hydroxylation of HIF in the presence of oxygen by a conserved family of Egl-nine (EGLN) enzymes. In the absence of pVHL, HIF becomes stabilized and is free to induce the expression of its target genes, many of which are important in regulating angiogenesis, cell growth, or cell survival. Moreover, preliminary data indicate that HIF plays a critical role in pVHL-defective tumor formation, raising the possibility that drugs directed against HIF or its downstream targets (such as vascular endothelial growth factor) might one day play a role in the treatment of hemangioblastoma and renal cell carcinoma. On the other hand, clear genotype-phenotype correlations are emerging in VHL disease and can be rationalized if pVHL has functions separate from its control of HIF.

Multiple pheochromocytomas and paragangliomas in a young patient carrying a SDHD gene mutation

We report a 13-year-old boy with an atypical manifestation of a multilocular paraganglioma. Surgical treatment was not curative despite extirpation of a left-sided abdominal paraganglioma. After surgery, the boy experienced several hypertensive crises. Further investigations including dopamine-positron emission tomography demonstrated bilateral adrenal tumours, a further right-sided paravertebral tumour as well as bilateral cervical glomus tumours. Genetic testing revealed a germline mutation in the succinate dehydrogenase subunit D (SDHD) gene.

CONCLUSION

The final diagnosis was familial pheochromocytoma/paraganglioma type 1 (OMIM 168000). Antihypertensive treatment was succesfull and improved the patient's quality of life.

[Paraganglioma in the area of the head and neck. A review of molecular genetic research]

Paragangliomas of the head and neck region are usually benign tumors that develop from chemoreceptors of paraganglionic origin in the majority of patients. These receptors play an important role in sensing and regulation of the blood CO(2) level. Genetic alterations in the mitochondrial enzyme complex II (SDH), which is involved in respiratory chain and citric acid cycle reactions, have been shown to lead to sporadic as well as familial cases of these tumors. The gene encoding the subunit SDHD shows mutations in up to 50% of these cases. In addition, loss of heterozygosity (LOH) was demonstrated in these tumor samples and has been shown to be connected with oncogenesis of paragangliomas. Thus, SDHD is the first known tumor suppressor gene encoding a mitochondrial protein. In this article we summarize the current state of knowledge concerning the development of paragangliomas.

Chromosome 11 monosomy in conjunction with a mutated SDHD initiation codon in nonfamilial paraganglioma cases

Paragangliomas of the head and neck region are a group of rare, usually benign, slow-growing tumors developing from paraganglionic chemoreceptors in most patients. Mutations in a subunit of the mitochondrial enzyme II complex (succinate dehydrogenase [SDHD]) were shown to be responsible for the formation of paragangliomas. In addition, loss of heterozygosity (LOH) on chromosome 11, mainly in 11q23 (PGL1), was observed recently. We analyzed DNA derived from tumor sections of three unrelated paraganglioma patients (one case with multiple paragangliomas, two cases with single tumors; all of them sporadic cases) for mutations in the SDHD gene by direct sequencing. Microsatellite-based LOH was performed, and events of chromosomal loss were validated by fluorescence in situ hybridization (FISH) on paraffin-embedded tumor and normal tissue by using centromeric satellite DNA. Sequence analysis revealed mutations in SDHD exon 1 in all patients, affecting the initiation codon (M1V). Another alteration was detected in exon 2 but was lacking in tumor DNA and therefore classified as polymorphism (H50R). LOH and FISH analyses demonstrated partial/total monosomy for chromosome 11 in the tumor samples tested. A common genetic mechanism appears to be the pathophysiologic basis for sporadic tumor development because the proposed two-hit model comprising both LOH and point mutation is manifest in our patients. Loss of chromosome 11 regions, including the deletion of PGL1 and PGL2 loci, may result in a more severe phenotype, as exemplified by the development of multiple tumors in one of the patients.

Genomic imprinting and environment in hereditary paraganglioma

Hereditary paraganglioma (PGL) is characterized by the development of slow-growing and vascularized tumors in the paraganglionic system. PGL is caused by germ line heterozygous inactivating mutations in the SDHB (PGL4), SDHC (PGL3), or SDHD (PGL1) genes, which encode three of the four subunits of mitochondrial complex II (succinate dehydrogenase; SDH). Common tumor sites include the carotid body in the neck and paraganglia in the abdomen. The risk of tumor development associated with SDHD mutations is determined by the sex of the transmitting parent, because only a paternal transmission leads to tumorigenesis in the progeny. This transmission pattern suggests operation of genomic imprinting on the SDHD gene. There is also evidence that the risk of tumor development increases at higher altitudes among SDHD mutation carriers. Accordingly, the increased prevalence of SDHD mutations in the Netherlands, attributable to multiple founder mutations, has been explained in part by the low altitudes in this country, which presumably reduce gene penetrance and relax the natural selection. Thus, PGL caused by SDHD mutations represents an unusual example of an inherited monogenic tumor syndrome because the risk of tumorigenesis shows an absolute dependence on the sex of the transmitting parent and may be modified by a ubiquitous environmental factor.

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

BACKGROUND

Germline mutations in three subunits of mitochondrial complex II (SDHB, SDHC and SDHD) may be associated with susceptibility to phaeochromocytoma (PC) and/or head and neck paraganglioma (HNPGL).

METHODS

To further define the role of SDH subunit mutations in these disorders, we analysed a series of 22 probands with PC and evidence of genetic susceptibility (seven with familial PC only, one with familial PC and HNPGL, 10 sporadic cases with multiple PC and four cases of isolated paediatric onset PC) for germline SDHB, SDHC and SDHD mutations. In addition, we analysed 34 cases of HNPGL (30 isolated cases with single tumours, three isolated cases with multiple tumours and one familial case with multiple tumours) for somatic and germline mutations in SDHB, SDHC and SDHD.

RESULTS

We identified four germline mutations (three SDHB and one SDHD, three novel) in the 22 PC probands. Combining these results with our previous series, we have detected germline SDHB or SDHD mutations in 2/12 (17%) of familial PC only kindreds, 4/5 (80%) of familial PC and HNPGL cases, 1/10 of sporadic multiple PC cases and 2/4 (50%) of paediatric PCs. No somatic mutations were detected in the HNPGL tumours, but four cases with multiple HNPGL had the common P81L germline SDHD mutation. Intriguingly a silent SNP (c.204C > T) in SDHD was significantly more common in HNPGL cases (6/34) than in controls (1/100, P = 0.0011). Combining our results with those from two other large studies in which both SDHB and SDHD have been analysed, SDHB mutations were most commonly associated with phaeochromocytoma susceptibility and SDHD with the development of HNPGL (P = 0.025). However, germline SDHB and SDHD mutations demonstrate considerable phenotypic variability and genotype-phenotype correlations are complex.

CONCLUSION

The significantly lower frequency (P = 0.028) of germline SDH subunit mutations in familial PC only cases compared to those with familial PC and HNPGL suggests that further PC susceptibility gene(s) remain to be identified.

Pheochromocytoma: the expanding genetic differential diagnosis

Pheochromocytomas and paragangliomas are tumors of the autonomic nervous system; pheochromocytomas are tumors of the adrenal medulla, and paragangliomas are extra-adrenal tumors arising from either the sympathetic nervous system or parasympathetic ganglia. It has previously been estimated that approximately 10%-15% of pheochromocytomas are due to hereditary causes. However, our increased understanding of the three hereditary syndromes (neurofibromatosis 1, multiple endocrine neoplasia type 2, and von Hippel-Lindau syndrome) in which pheochromocytoma is found and the recent discovery that mutations in genes in the succinate dehydrogenase family (SDHB and SDHD) predispose to pheochromocytoma have necessitated a re-evaluation of the genetic basis of pheochromocytoma. These studies indicate that the frequency of germline mutations associated with isolated pheochromocytoma is higher than previously estimated, with both hospital-based series and a large population-based series indicating that the frequency of germline mutations in RET, VHL, SDHB, and SDHD taken together approximates 20%. In all patients with pheochromocytoma, including those with known hereditary syndrome or a positive family history, the frequency of germline mutations in these four genes together approaches 30%. Given the frequency of germline mutations, consideration should be given to genetic counseling for all patients with pheochromocytoma and is particularly important for individuals with a positive family history, multifocal disease, or a diagnosis before age 50. Identification of patients with hereditary pheochromocytoma is important because it can guide medical management in mutation-positive patients and their families. This review provides an overview of the known genetic syndromes that are commonly associated with pheochromocytoma, examines recent data on the association of germline mutations in the succinate dehydrogenase gene family with pheochromocytoma, and suggests guidelines for the genetic evaluation of pheochromocytoma patients.

Altitude is a phenotypic modifier in hereditary paraganglioma type 1: evidence for an oxygen-sensing defect

Hereditary paraganglioma type 1 (PGL1) is characterized by slow-growing and vascularized tumors that often develop in the carotid body (CB) and is caused by mutations in the gene for succinate dehydrogenase D ( SDHD) of mitochondrial complex II. The mechanisms of tumorigenesis and the factors affecting penetrance and expressivity are unknown. Because chronic hypoxic stimulation at high altitudes causes sporadic CB paragangliomas, it has been hypothesized that the SDHD gene product may be involved in oxygen sensing. On this background, we examined genotype-phenotype-environment relationships and tested whether higher altitudes adversely affect the phenotype in PGL1. An analysis of 58 subjects from 23 families revealed that nonsense/splicing mutation carriers developed symptoms 8.5 years earlier than missense mutation carriers ( P<0.012). We also found that subjects who were diagnosed with single tumors at their first clinical evaluation lived at lower average altitudes and were exposed to lower altitude-years than those with multiple tumors ( P<0.012). Pheochromocytomas developed in six subjects (approximately 10%), five of whom had nonsense mutations ( P=0.052). Subjects with pheochromocytomas also lived at higher average altitudes and were exposed to higher altitude-years than those without them ( P=0.026). To test whether altitude is also associated with the more frequent detection of germ-line founder mutations among sporadic cases in The Netherlands than in the USA ( P=0.00033), we calculated population-weighted elevations of the two countries. We found that the population-weighted elevations were approximately 260 m for the US and 2 m for the central-western Netherlands ( P~0), where three Dutch founder mutations were discovered. This finding suggests that low altitudes in The Netherlands reduce penetrance and relax the natural selection on SDHD mutations. Collectively, these data suggest that higher altitudes and nonsense/splicing mutations are associated with phenotypic severity in PGL1 and support the hypothesis that SDHD mutations impair oxygen sensing.

Vascular malformations: localized defects in vascular morphogenesis

Vascular anomalies are localized defects of the vasculature, and usually affect a limited number of vessels in a restricted area of the body. They are subdivided into vascular malformations and vascular tumours. Most are sporadic, but Mendelian inheritance is observed in some families. By genetic analysis, several causative genes have been identified during the last 10 years. This has shed light into the pathophysiological pathways involved. Interestingly, in most cases, the primary defect seems to affect the characteristics of endothelial cells. Only mutations in the glomulin gene, responsible for hereditary glomuvenous malformations, are thought to directly affect vascular smooth-muscle cells.

A novel mutation in the SDHD gene in a family with inherited paragangliomas--implications of genetic diagnosis for follow up and treatment

BACKGROUND

Early detection of paragangliomas (PGs) has been linked to low morbidity after surgical resection. Recent identification of causative genes (SDHB, SDHC, and SDHD) has made it possible to detect individuals at high risk for tumors.

METHODS

We identified a three-generation family, with four individuals affected with PGs. Because pedigree analysis suggested maternal imprinting (the phenotype is present only if inherited through the paternal line), the SDHD gene (PGL1) was screened.

RESULTS

A novel mutation that causes skipping of exon 3 was identified. Ten of the seventeen tested individuals carried the mutation. All six clinically unaffected individuals inherited the mutation from their mother. Five of them are men, with a 50% risk for affected progeny.

CONCLUSIONS

To allow early treatment with low morbidity, genetic counseling is needed when familial paraganglioma is suspected. Asymptomatic carriers should be followed by cervical MRI. In addition, because pheochromocytomas may occur, catecholamine excretion can be performed. This screening should probably be proposed at 5 to 10 years of age.