Molecular characterization of novel germline deletions affecting SDHD and SDHC in pheochromocytoma and paraganglioma patients

A major cause of paraganglioma and pheochromocytoma is germline mutation of the tumor suppressor genes SDHB, SDHC, and SDHD, encoding subunits of succinate dehydrogenase (SDH). While many SDH missense/nonsense mutations have been identified, few large deletions have been described. We performed multiplex ligation-dependent probe amplification deletion analysis in 126 point mutation-negative patients, and here we describe four novel deletions of SDHD and SDHC. Long-range PCR was used for the fine mapping of deletions. One patient had a 10 kb AluSg-AluSx-mediated deletion including SDHD exons 1 and 2, the entire TIMM8B gene, and deletion of exons of C11orf57. A second patient had a deletion of SDHD exons 1 and 2 and exon 1 of the TIMM8B gene. A third patient showed a deletion of exon 2 of SDHD, together with a 235 bp MIRb-Tensin gene insertion. In a fourth patient, a deletion of exons 5 and 6 of the SDHC gene was found, only the second SDHC deletion currently known. The deletions of the TIMM8B and C11orf57 genes are the first to be described, but do not appear to result in an additional phenotype in these patients. Four of the eight breakpoints occurred in Alu sequences and all three SDHD deletions showed an intron 2 breakpoint. This study underlines the fact that clinically relevant deletions may encompass neighboring genes, with the potential to modify phenotype. Gene deletions of SDHD and SDHC represent a substantial proportion of all mutations, and must be considered in paraganglioma patients shown to be negative for mutations by sequencing.

Pheochromocytomas: from genetic diversity to new paradigms

Pheochromocytomas and paragangliomas are catecholamine-secreting tumors of neural crest origin caused by germline mutations in at least six distinct genes. This genetic heterogeneity has provided a rich source for both the discovery and functional characterization of new tumor-related genes. However, the genetic repertoire of these tumors is still not fully known, and current evidence points to the existence of additional pheochromocytoma susceptibility genes. Here, the unique contributions of three hereditary models of pheochromocytoma that can advance our knowledge of the disease pathogenesis are presented. The first model, loss of succinate dehydrogenase (SDH) function, illustrates how SDHB, C, or D mutations, components of the energy metabolism pathway, serve as a unique system to explore the pervasive metabolic shift of cancer cells towards glycolysis as a source of energy (also known as the Warburg effect) in contrast to the characteristic oxidative phosphorylation of normal cells. In the second model, mechanisms of tumorigenesis distinct from classical pheochromocytoma susceptibility genes are discussed in the context of a novel putative suppressor of neural crest-derived tumors, the KIF1B beta gene. Finally, NF1 loss is highlighted as a valuable study model to investigate the cell lineage selectivity of the Egln3-mediated developmental apoptotic defect of chromaffin precursor cells. Results from these studies may offer clues to understand the tissue specificity of hereditary pheochromocytoma syndromes. These distinct hereditary disease models illustrate how genetic-driven progress has the potential to narrow current gaps in our knowledge of pheochromocytoma and paraganglioma pathogenesis.

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.

The approach to the patient with paraganglioma

The multidisciplinary management of patients with paragangliomas and pheochromocytomas remains challenging. The cornerstone of excellent multidisciplinary management of such patients is genetic classification and management in a tertiary care referral center. Up to one third of all symptomatic presentations of pheochromocytoma or paraganglioma are due to germline mutations in one of six genes defining multiple endocrine neoplasia type 2, von Hippel-Lindau disease, neurofibromatosis type 1, and the paraganglioma syndromes types 1, 3, and 4. This genetic classification forms the basis early diagnosis and follow-up including management of relatives. Easily available clinical information such as tumor location and number, age, gender, and family history must be used to prioritize which gene should be tested. Mutation carriers should undergo regular check-up to detect and treat metachronous paraganglial and extraparaganglial tumors, and depending on syndrome, other extraparaganglial neoplasias such as medullary thyroid cancer and renal clear cell carcinomas in time. Adrenal and extraadrenal retroperitoneal tumors should be operated by surgeons highly experienced in minimal invasive, endoscopic techniques.

The succinate dehydrogenase genetic testing in a large prospective series of patients with paragangliomas

CONTEXT

Germline mutations in SDHx genes cause hereditary paraganglioma.

OBJECTIVE

The aim of the study was to assess the indications for succinate dehydrogenase (SDH) genetic testing in a prospective study.

DESIGN

A total of 445 patients with head and neck and/or thoracic-abdominal or pelvic paragangliomas were recruited over 5 yr in 20 referral centers. In addition to classical direct sequencing of the SDHB, SDHC, and SDHD genes, two methods for detecting large genomic deletions or duplications were used, quantitative multiplex PCR of short fluorescent fragments (QMPSF) and multiplex ligation-dependent probe amplification (MLPA).

RESULTS

A large variety of SDH germline mutations were found by direct sequencing in 220 patients and by QMPSF and MLPA in 22 patients (9.1%): 130 in SDHD, 96 in SDHB, and 16 in SDHC. Mutation carriers were younger and more frequently had multiple or malignant paraganglioma than patients without mutations. A head and neck paraganglioma was present in 97.7% of the SDHD and 87.5% of the SDHC mutation carriers, but in only 42.7% of the SDHB carriers. A thoracic-abdominal or pelvic location was present in 63.5% of the SDHB, 16.1% of the SDHD, and in 12.5% of the SDHC mutation carriers. Multiple paragangliomas were diagnosed in 66.9% of the SDHD mutation carriers. A malignant paraganglioma was documented in 37.5% of the SDHB, 3.1% of the SDHD, and none of the SDHC mutation carriers.

CONCLUSIONS

SDH genetic testing, including tests for large genomic deletions, is indicated in all patients with head and neck and/or thoracic-abdominal or pelvic paraganglioma and can be targeted according to clinical criteria.

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.

Pheochromocytomas and extra-adrenal paragangliomas detected by screening in patients with SDHD-associated head-and-neck paragangliomas

Patients with SDHD-associated head-and-neck paragangliomas (HNP) are at risk for developing pheochromocytomas for which screening has been advised. To assess clinical, biochemical, and radiological outcomes of screening in a large single-center cohort of SDHD-positive patients with HNP and to address the necessity for repetitive follow-up, we evaluated 93 patients with SDHD-associated HNP (p.Asp92Tyr, p.Leu139Pro). Screening consisted of measurement of 24 h urinary excretion of catecholamines and/or their metabolites in duplicate, which was repeated with intervals of 2 years if initial biochemical screening was negative. In patients, in whom urinary excretion was above the reference limit, imaging studies with (123)I-MIBG (metaiodobenzylguanidine) scintigraphy and magnetic resonance imaging (MRI) and/or computed tomography (CT) were performed. Pheochromocytomas and extra-adrenal paragangliomas were treated surgically after appropriate blockade. Median follow-up was 4.5 years (range 0.5-19.5 years). Twenty-eight out of the 93 patients were included in our study and underwent additional imaging for pheochromocytomas/extra-adrenal paragangliomas. In 11 out of the 28 patients intra-adrenal pheochromocytomas were found. Extra-adrenal paragangliomas were discovered in eight patients. These tumors were detected during initial screening in 63% of cases, whereas 37% were detected after repeated biochemical screening. One patient was diagnosed with a biochemically silent pheochromocytoma. The high prevalence of pheochromocytomas/extra-adrenal paragangliomas in patients with SDHD-associated HNP warrants regular screening for tumors in these patients. Paragangliomas that do not secrete catecholamines might be more prevalent than previously reported. Future studies will have to establish whether routine imaging studies should be included in the screening of SDHD mutation carriers, irrespective of biochemical screening.

Clinical aspects of SDHx-related pheochromocytoma and paraganglioma

Paragangliomas (PGLs) derive from either sympathetic chromaffin tissue in adrenal and extra-adrenal abdominal or thoracic locations, or from parasympathetic tissue of the head and neck. Mutations of nuclear genes encoding subunits B, C, and D of the mitochondrial enzyme succinate dehydrogenase (SDHB 1p35-p36.1, SDHC 1q21, SDHD 11q23) give rise to hereditary PGL syndromes PGL4, PGL3, and PGL1 respectively. The susceptibility gene for PGL2 on 11q13.1 remains unidentified. Mitochondrial dysfunction due to SDHx mutations have been linked to tumorigenesis by upregulation of hypoxic and angiogenesis pathways, apoptosis resistance and developmental culling of neuronal precursor cells. SDHB-, SDHC-, and SDHD-associated PGLs give rise to more or less distinct clinical phenotypes. SDHB mutations mainly predispose to extra-adrenal, and to a lesser extent, adrenal PGLs, with a high malignant potential, but also head and neck paragangliomas (HNPGL). SDHD mutations are typically associated with multifocal HNPGL and usually benign adrenal and extra-adrenal PGLs. SDHC mutations are a rare cause of mainly HNPGL. Most abdominal and thoracic SDHB-PGLs hypersecrete either norepinephrine or norepinephrine and dopamine. However, only some hypersecrete dopamine, are biochemically silent. The biochemical phenotype of SDHD-PGL has not been systematically studied. For the localization of PGL, several positron emission tomography (PET) tracers are available. Metastatic SDHB-PGL is the best localized by [(18)F]-fluorodeoxyglucose PET. The identification of SDHx mutations in patients with PGL is warranted for a tailor-made approach to the biochemical diagnosis, imaging, treatment, follow-up, and family screening.

Mutations and polymorphisms in the SDHB, SDHD, VHL, and RET genes in sporadic and familial pheochromocytomas

The prevalence of germ line mutations within the RET-protooncogene and the tumor suppressor genes SDHB, SDHD, and VHL in pheochromocytomas (PC) varies in recent studies from 12 to 24%, if one look at them collectively. DNA was extracted from frozen tumor tissue as well as from blood leukocytes of 36 PC (26 sporadic/10 MEN2). Exons 1-8 of the SDHB-gene, 1-4 of the SDHD-gene, 1-3 of the VHL-gene, and exons 10, 11, 13, 14, 16 of the RET-gene were amplified by PCR and analyzed by DHPLC with the Transgenomic WAVE-System. Samples with aberrant wave profiles were subjected to direct sequencing. Genetic aberrations were correlated to clinical characteristics. Germ line mutations in sporadic PC were identified in four patients (11%) whereas somatic mutations were observed in two (5%) patients. Nine coding polymorphisms (PM) were identified in seven (19%) patients. Intronic variants were observed in six (17%) patients and were all located in the SHDB gene. Patients with wild type alleles in all assessed genes were older (53 vs. 37 years, P = 0.007) and presented with an increased tumor size (49 vs. 32 mm, P = 0.003) compared to patients with mutations. Malignant PC revealed multiple (>2) genetic alterations more frequently than benign PC (4/7 vs. 4/29, P = 0.03). Interestingly intronic variants of the SDHB gene occur more frequently in malignant than in benign PC (3/7 vs. 2/29, P = 0.04). The frequency of germ line mutations in sporadic pheochromocytomas was lower in our cohort than previously reported. Polymorphisms of the RET gene are common (17%) and occur in familial and sporadic PC. Multiple genetic alterations including mutations, polymorphisms and intronic variants are more frequently observed in malignant PC.

Contrasting clinical manifestations of SDHB and VHL associated chromaffin tumours

Mutations in succinate dehydrogense-B (SDHB) and the von Hippel-Lindau (VHL) genes result in an increased risk of developing chromaffin tumours via a common aetiological pathway. The aim of the present retrospective study was to compare the clinical phenotypes of disease in subjects developing chromaffin tumours as a result of SDHB mutations or VHL disease. Thirty-one subjects with chromaffin tumours were assessed; 16 subjects had SDHB gene mutations and 15 subjects had a diagnosis of VHL. VHL-related tumours were predominantly adrenal phaeochromocytomas (22/26; 84.6%), while SDHB-related tumours were predominantly extra-adrenal paragangliomas (19/25; 76%). Median age at onset of the first chromaffin tumour was similar in the two cohorts. Tumour size was significantly larger in the SDHB cohort in comparison with the VHL cohort (P=0.002). Multifocal disease was present in 9/15 (60%) of the VHL cohort (bilateral phaeochromocytomas) and only 3/16 (19%) of the SDHB cohort, while metastatic disease was found in 5/16 (31%) of the SDHB cohort but not in the VHL cohort to date. The frequency of symptoms, hypertension and the magnitude of catecholamine secretion appeared to be greater in the SDHB cohort. Renal cell carcinomas were a feature in 5/15 (33%) of the VHL cohort and 1/16 (6%) of the SDHB cohort. These data indicate that SDHB-related tumours are predominantly extra-adrenal in location and associated with higher catecholamine secretion and more malignant disease, in subjects who appear more symptomatic. VHL-related tumours tend to be adrenal phaeochromocytomas, frequently bilateral and associated with a milder phenotype.

Head and neck paragangliomas in von Hippel-Lindau disease and multiple endocrine neoplasia type 2

BACKGROUND

Head and neck paragangliomas (HNPs) occur as sporadic or familial entities, the latter mostly in association with germline mutations of the SDHB, SDHC, or SDHD (SDHx) genes. Heritable non-SDHx HNP might occur in von Hippel-Lindau disease (VHL, VHL gene), multiple endocrine neoplasia type 2 (MEN2, RET gene), and neurofibromatosis type 1 (NF1, NF1 gene). Reports of non-SDHx HNP presentations are scarce and guidance for genetic testing nonexistent.

PATIENTS AND METHODS

An international consortium registered patients with HNPs and performed mutation analyses of the SDHx, VHL, and RET genes. Those with SDHx germline mutations were excluded for purposes of this study. Personal and family histories were evaluated for paraganglial tumors, for the major tumor manifestations, and for family history of VHL, MEN2, or NF1.

RESULTS

Twelve patients were found to have hereditary non-SDHx HNPs of a total of 809 HNP and 2084 VHL registrants, 11 in the setting of germline VHL mutations and one of a RET mutation. The prevalence of hereditary HNP is five in 1000 VHL patients and nine in 1000 non-SDHx HNP patients. Comprehensive literature review revealed previous reports of HNPs in five VHL, two MEN2, and one NF1 patient. Overall, 11 here presented HNP cases, and four previously reported VHL-HNPs had lesions characteristic for VHL and/or a positive family history for VHL.

CONCLUSIONS

Our observations provide evidence that molecular genetic testing for VHL or RET germline mutations in patients with HNP should be done only if personal and/or family history shows evidence for one of these syndromes.

A nuclear gene encoding the iron-sulfur subunit of mitochondrial complex II is regulated by B3 domain transcription factors during seed development in Arabidopsis

Mitochondrial complex II (succinate dehydrogenase) is part of the tricarboxylic acid cycle and the respiratory chain. Three nuclear genes encode its essential iron-sulfur subunit in Arabidopsis (Arabidopsis thaliana). One of them, SUCCINATE DEHYDROGENASE2-3 (SDH2-3), is specifically expressed in the embryo during seed maturation, suggesting that SDH2-3 may have a role as the complex II iron-sulfur subunit during embryo maturation and/or germination. Here, we present data demonstrating that three abscisic acid-responsive elements and one RY-like enhancer element, present in the SDH2-3 promoter, are involved in embryo-specific SDH2-3 transcriptional regulation. Furthermore, we show that ABSCISIC ACID INSENSITIVE3 (ABI3), FUSCA3 (FUS3), and LEAFY COTYLEDON2, three key B3 domain transcription factors involved in gene expression during seed maturation, control SDH2-3 expression. Whereas ABI3 and FUS3 interact with the RY element in the SDH2-3 promoter, the abscisic acid-responsive elements are shown to be a target for bZIP53, a member of the basic leucine zipper (bZIP) family of transcription factors. We show that group S1 bZIP53 protein binds the promoter as a heterodimer with group C bZIP10 or bZIP25. To the best of our knowledge, the SDH2-3 promoter is the first embryo-specific promoter characterized for a mitochondrial respiratory complex protein. Characterization of succinate dehydrogenase activity in embryos from two homozygous sdh2-3 mutant lines permits us to conclude that SDH2-3 is the major iron-sulfur subunit of mature embryo complex II. Finally, the absence of SDH2-3 in mutant seeds slows down their germination, pointing to a role of SDH2-3-containing complex II at an early step of germination.

Flexibility in anaerobic metabolism as revealed in a mutant of Chlamydomonas reinhardtii lacking hydrogenase activity

The green alga Chlamydomonas reinhardtii has a network of fermentation pathways that become active when cells acclimate to anoxia. Hydrogenase activity is an important component of this metabolism, and we have compared metabolic and regulatory responses that accompany anaerobiosis in wild-type C. reinhardtii cells and a null mutant strain for the HYDEF gene (hydEF-1 mutant), which encodes an [FeFe] hydrogenase maturation protein. This mutant has no hydrogenase activity and exhibits elevated accumulation of succinate and diminished production of CO2 relative to the parental strain during dark, anaerobic metabolism. In the absence of hydrogenase activity, increased succinate accumulation suggests that the cells activate alternative pathways for pyruvate metabolism, which contribute to NAD(P)H reoxidation, and continued glycolysis and fermentation in the absence of O2. Fermentative succinate production potentially proceeds via the formation of malate, and increases in the abundance of mRNAs encoding two malate-forming enzymes, pyruvate carboxylase and malic enzyme, are observed in the mutant relative to the parental strain following transfer of cells from oxic to anoxic conditions. Although C. reinhardtii has a single gene encoding pyruvate carboxylase, it has six genes encoding putative malic enzymes. Only one of the malic enzyme genes, MME4, shows a dramatic increase in expression (mRNA abundance) in the hydEF-1 mutant during anaerobiosis. Furthermore, there are marked increases in transcripts encoding fumarase and fumarate reductase, enzymes putatively required to convert malate to succinate. These results illustrate the marked metabolic flexibility of C. reinhardtii and contribute to the development of an informed model of anaerobic metabolism in this and potentially other algae.

When should genetic testing be obtained in a patient with phaeochromocytoma or paraganglioma?

About 30% of phaeochromocytoma and paraganglioma patients harbour a germline mutation in one of the known susceptibility genes and in more than one-third of these patients there is no family history for these tumours. The genetic classification, risk assessment and specific management of the patients and at risk family members play an important role in preventive medicine. Distinct diagnostic or therapeutic approaches related to the genetic testing results are and will be even more relevant in the future for the detection of mutation carriers. In addition to a positive family history, other clinical features such as young age at time of manifestation, multifocal tumours and specific tumour location are highly associated with the presence of a germline mutation - genetic testing in these cases should be mandatory. Since several genes are involved in the genetics of phaeochromocytoma and paraganglioma, prioritizing which gene(s) to be tested first by using simple clinical information can reduce the efforts and costs of this analysis. The clinicians offering and performing the genetic testing should provide or make available adequate counselling as well as access to preventive and surveillance options to patients. Collaboration with referral centres and research groups in this field can help to coordinate the management of these patients.

Mediastinal paragangliomas: association with mutations in the succinate dehydrogenase genes and aggressive behavior

Extra-adrenal pheochromocytomas, otherwise known as paragangliomas (PGLs), account for about 20% of catecholamine-producing tumors. Catecholamine excess and mutations in the genes encoding succinate dehydrogenase subunits (SDHx) are frequently found in patients with PGLs. Only 2% of PGLs are found in the mediastinum, and little is known about genetic alterations in patients with mediastinal PGLs, catecholamine production by these tumors, or their clinical behavior. We hypothesized that most mediastinal PGLs are associated with germ line SDHx mutations, norepinephrine and/or dopamine excess, and aggressive behavior. The objective of this study was to characterize genetic, biochemical, and clinical data in a series of ten patients with mediastinal PGLs. All ten primary mediastinal PGL patients had germ line SDHx mutations, six in SDHB, and four in SDHD genes. Chest or back pain were the most common presenting symptoms (five patients), and catecholamines and/or their metabolites were elevated in seven patients. Additional tumors included head and neck PGLs in four patients, pheochromocytoma in one patient, and bladder PGL in another. Metastatic disease was documented in six patients (60%), and a concurrent abdominal mass was found in one patient. We conclude that mediastinal PGLs are strongly associated with SDHB and SDHD gene mutations, noradrenergic phenotype, and aggressive behavior. The present data suggest that all patients with mediastinal PGLs should be screened for SDHx gene mutations, regardless of age.

Malignant extra-adrenal pheochromocytoma caused by an SDHB intronic variation leading to a 54-bp deletion in exon 4

In the last few years several papers have reported on the association between mutations of the genes encoding the structural (SDHC, SDHD) and catalytic (SDHB) subunits of succinate dehydrogenase and the occurrence of hereditary pheochromocytomas/paragangliomas (Pheo/PGL) syndromes. We diagnosed a malignant extraadrenal Pheo in a 38-yr-old man with abdominal lesions; many areas of increased uptake at octreoscan scintigraphy in the skeleton indicated metastatic disease. We then approached genetic analysis through the screening of the SDHB, SDHC, and SDHD genes. Here we report a heterozygous G>A transversion at position +1 of intron 4 of SDHB gene. To clarify this mutation we performed cDNA analysis by RT-PCR and we assume that the splice site mutation in intron 4 abolishes the consensus splice donor sequence leading to an in-frame deletion of 18 amino acid. This finding indicates once again that SDHB mutations could predispose to malignant Pheo.

Familial pheochromocytoma

Pheochromocytomas and Paragangliomas (PGL) form the group of paraganglial tumours which can occur in any paraganglia from the skull base to the pelvic floor. The terminology is not uniform. While the World Health Organization (WHO) applies pheochromocytoma exclusively to adrenal tumours, many clinicians use the term pheochromocytoma also for extra-adrenal abdominal and thoracic tumours, since by tradition pheochromocytoma is a vasoactive tumour. In contrast, head and neck paraganglioma is mostly only a space-occupying mass. The diagnosis is confirmed by both biochemical testing and radiological imaging. One third of patients with pheochromocytomas and paragangliomas are carriers of germline mutations in one of 6 genes and thus have a hereditary disorder. About 1% of Neurofibromatosis (NF) 1 patients have pheochromocytomas. All pheochromocytoma patients with NF 1 also show cutaneous lesions. About 50% of MEN2 patients harbour pheochromocytoma. The dominant lesion in this entity is Medullary Thyroid Carcinoma (MTC) occurring in up to 100% of patients. Von Hippel-Lindau disease (VHL)is found in about 20% of patients in association with pheochromocytoma. VHL is classified as type 1 predominantly without and type 2 predominantly with pheochromocytoma. Other important components of VHL are hemangioblastomas of the eye and Central Nervous System (CNS), renal clear cell carcinoma, multiple pancreatic cysts and islet cell carcinoma. PGL syndromes have been genetically characterized as PGL 1, 3 and 4 and are caused by mutations in the succinate dehydrogenase (SDH) subunit D, C and B genes, respectively (SDHD, SDHC and SDHB). Paraganglioma syndromes include predisposition to paraganglial tumours in any location, whereas PGL 3 patients mostly show only head and neck paragangliomas. All syndromes associated with paraganglial tumours are autosomal dominantly transmitted, but patients with SDHD mutations develop tumours only if they inherit the mutation from the father. Familial paraganglial tumours are characterized by younger age at diagnosis and more frequently multifocal and extra-adrenal abdominal pheochromocytomas. Patients with PGL 4 and less frequently VHL, are particularly predisposed to malignant pheochromocytoma. Endoscopic surgery is the primary treatment for pheochromocytoma. For malignant cases, chemotherapeutic as well as radionuclear approaches are available. No specific treatment has been proposed for prevention of the disease in inherited disorders. Thus, early diagnosis and regular follow-up are the only means for a better outcome.

Medullary thyroid cancer: molecular biology and novel molecular therapies

Medullary thyroid cancer (MTC) arises from neural-crest-derived parafollicular C cells of the thyroid gland and accounts for approximately 4% of all thyroid cancers. Up to 25-30% of MTC cases occur as inherited disorders while the remaining cases represent the sporadic form of the disease. In this review, the structure and signalling properties of the RET proto-oncogene in its wild-type and mutant forms, and its role in hereditary and sporadic MTC, are discussed. A full data search was performed through PubMed over the years 2000-2008 with the key words 'medullary thyroid cancer, treatment, molecular biology, RET, molecular mechanism', and all relevant publications have been included, together with selected publications prior to that date. We also review novel therapies for metastatic MTC, especially the tyrosine kinase inhibitors which have activity at multiple receptor subtypes, and summarize the current ongoing trials in this area. While such tyrosine kinase inhibitors, particularly those affecting RET activity such as vandetanib, sorafenib and sunitinib, are promising, the low rate of partial responses and absence of complete responses in all of the various trials of monotherapy emphasize the need for new and more effective single agents or combinations of therapeutic agents with acceptable toxicity.

Predominant expression of mutated allele of the succunate dehydrogenase D (SDHD) gene in the SDHD-related paragangliomas

Recent studies indicate that succinate dehydrogenase (SDH) genes B, C, or D are, at least partly, involved in the pathogenesis of pheochromocytoma or paraganglioma. Of these three genes, the SDHD gene mutation is most closely related with paragangliomas of the neck. Here we describe a case of an SDHD-related paraganglioma, in which we studied the molecular characteristics of an SDHD mutation to evaluate the involvement of SDHD in neck paragangliomas. Genetic testing revealed a heterozygous G106D mutation in the SDHD gene. In the tumor tissue, loss of heterozygosity was demonstrated by real time polymerase chain reaction (PCR). In the present case of SDHD mutated paragangliomas, wild type SDHD gene expression was markedly reduced possibly due to loss of heterozygosity not due to imprinting of SDHD gene in the tumors.

Novel mutation (L157X) in the succinate dehydrogenase B gene (SDHB) in a Japanese family with abdominal paraganglioma following lung metastasis

Recently, nuclear genes encoding two mitochondrial complex II subunit proteins, SDHD and SDHB, have been found to be associated with the development of familial pheochromocytomas and paragangliomas (hereditary pheochromocytoma/paraganglioma syndrome: HPPS). Growing evidence suggests that the mutation of SDHB is highly associated with abdominal paraganglioma and the following distant metastasis (malignant paraganglioma). In the present study, we report the case of a novel SDHB mutation (L157X) in a Japanese patient with abdominal paraganglioma following malignant lung metastasis. In addition, we identified an asymptomatic carrier of the SDHB mutation in this family.

Biochemically silent abdominal paragangliomas in patients with mutations in the succinate dehydrogenase subunit B gene

CONTEXT

Patients with adrenal and extra-adrenal abdominal paraganglioma (PGL) almost invariably have increased plasma and urine concentrations of metanephrines, the O-methylated metabolites of catecholamines. We report four cases of biochemically silent abdominal PGL, in which metanephrines were normal despite extensive disease.

OBJECTIVE

Our objective was to identify the mechanism underlying the lack of catecholamine hypersecretion and metabolism to metanephrines in biochemically silent PGL.

DESIGN

This is a descriptive study.

SETTING

The study was performed at a referral center.

PATIENTS

One index case and three additional patients with large abdominal PGL and metastases but with the lack of evidence of catecholamine production, six patients with metastatic catecholamine-producing PGL and a mutation of the succinate dehydrogenase subunit B (SDHB) gene, and 136 random patients with catecholamine-producing PGL were included in the study.

MAIN OUTCOME MEASURES

Plasma, urine, and tumor tissue concentrations of catecholamines and metabolites were calculated with electron microscopy and tyrosine hydroxylase immunohistochemistry.

RESULTS

All four patients with biochemically silent PGL had an underlying SDHB mutation. In the index case, the tumor tissue concentration of catecholamines (1.8 nmol/g) was less than 0.01% that of the median (20,410 nmol/g) for the 136 patients with catecholamine-producing tumors. Electron microscopy showed the presence of normal secretory granules in all four biochemically silent PGLs. Tyrosine hydroxylase immunoreactivity was negligible in the four biochemically silent PGLs but abundant in catecholamine-producing PGLs.

CONCLUSIONS

Patients with SDHB mutations may present with biochemically silent abdominal PGLs due to defective catecholamine synthesis resulting from the absence of tyrosine hydroxylase. Screening for tumors in patients with SDHB mutations should not be limited to biochemical tests of catecholamine excess.