A review of the tumour spectrum of germline succinate dehydrogenase gene mutations: Beyond phaeochromocytoma and paraganglioma

The citric acid cycle, also known as the Krebs cycle, plays an integral role in cellular metabolism and aerobic respiration. Mutations in genes encoding the citric acid cycle enzymes succinate dehydrogenase, fumarate hydratase and malate dehydrogenase all predispose to hereditary tumour syndromes. The succinate dehydrogenase enzyme complex (SDH) couples the oxidation of succinate to fumarate in the citric acid cycle and the reduction of ubiquinone to ubiquinol in the electron transport chain. A loss of function in the succinate dehydrogenase (SDH) enzyme complex is most commonly caused by an inherited mutation in one of the four SDHx genes (SDHA, SDHB, SDHC and SDHD). This mechanism was first implicated in familial phaeochromocytoma and paraganglioma. However, over the past two decades the spectrum of tumours associated with SDH deficiency has been extended to include gastrointestinal stromal tumours (GIST), renal cell carcinoma (RCC) and pituitary adenomas. The aim of this review is to describe the extended tumour spectrum associated with SDHx gene mutations and to consider how functional tests may help to establish the role of SDHx mutations in new or unexpected tumour phenotypes.     

Genetic testing and surveillance guidelines in hereditary pheochromocytoma and paraganglioma

Pheochromocytoma and paraganglioma (PPGL) are rare tumours and at least 30% are part of hereditary syndromes. Approximately 20% of hereditary PPGL are caused by pathogenic germ line variants in genes of the succinate dehydrogenase complex (SDHx), TMEM127 or MAX. Herein we present guidelines regarding genetic testing of family members and their surveillance based on a thorough literature review. All cases of PPGL are recommended genetic testing for germ line variants regardless of patient and family characteristics. At minimum, FH, NF1, RET, SDHB, SDHD and VHL should be tested. In addition, testing of MEN1, SDHA, SDHAF2, SDHC, TMEM127 and MAX is recommended. Healthy first‐degree relatives (and second‐degree relatives in the case of SDHD and SDHAF2 which are maternally imprinted) should be offered carrier testing. Carriers of pathogenic variants should be offered surveillance with annual biochemical measurements of methoxy‐catecholamines and bi‐annual rapid whole‐body magnetic resonance imaging and clinical examination. Surveillance should start 5 years before the earliest age of onset in the family and thus only children eligible for surveillance should be offered pre‐symptomatic genetic testing. The surveillance of children younger than 15 years needs to be individually designed. Our guidelines will provide a framework for patient management with the possibility to follow outcome via national registries and/or follow‐up studies. Together with improved insights into the disease, this may enable optimisation of the surveillance scheme in order to minimise both anxiety and medical complications while ensuring early disease detection.     

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.     

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.     

Is there an optimal preoperative management strategy for phaeochromocytoma/paraganglioma?

Phaeochromocytomas and paragangliomas (PPGLs) are catecholamine secreting neuroendocrine tumours that predispose to haemodynamic instability. Currently, surgery is the only available curative treatment, but carries potential risks including hypertensive and hypotensive crises, cardiac arrhythmias, myocardial infarction and stroke, due to tumoral release of catecholamines during anaesthetic induction and tumour manipulation. The mortality associated with surgical resection of PPGL has significantly improved from 20–45% in the early 20th century (Apgar & Papper, AMA Archives of Surgery, 1951, 62 , 634) to 0–2·9% in the early 21st century (Kinney et al. Journal of Cardiothoracic and Vascular Anesthesia, 2002, 16 , 359), largely due to availability of effective pharmacological agents and advances in surgical and anaesthetic practice. However, surgical resection of PPGL still poses significant clinical management challenges. Preoperatively, alpha‐adrenoceptor blockade is the mainstay of management, although various pharmacological strategies have been proposed, based largely on reports derived from retrospective data sets. To date, no consensus has been reached regarding the ‘ideal’ preoperative strategy due, in part, to a paucity of data from high‐quality evidence‐based studies comparing different treatment regimens. Here, based on the available literature, we address the Clinical Question: Is there an optimal preoperative management strategy for PPGL?     

Risk of colorectal polyps and of malignancies in asymptomatic carriers of mutations in the main DNA mismatch repair genes

Objective: Mutation carriers (Mut+) in DNA mismatch repair genes are predisposed to cancer of various organs and to adenomatous polyps; however, they may remain asymptomatic and cancer or polyp-free for several years. We purposed to analyse the clinical follow-up of individuals carrying constitutional mutations in the MLH1, MSH2 or MSH6 genes who were unaffected by benign polyps or malignant tumours at diagnosis.

Material and Methods: Mut?+?subjects (n.81) were members of Lynch syndromes in whom mutations were detected between 1993 and 2015; all were asymptomatic at diagnosis. They were informed of the cancer risk and surveillance was suggested. As controls, 113 nongene carriers (Mut?) in the same Lynch families were identified.

Results: About one-fourth of the mutation carriers developed polyps, mostly adenomas; polyps were less (12%, p?MLH1 vs. MSH2 mutation carriers. In Mut+, 21 malignant tumours developed in 14 carriers vs. 4 tumours in 3 patients among Mut? (p?Conclusions: Cancer developed more often in Mut+, with no consistent difference between MLH1 and MSH2 carriers. More polyps (mostly adenomas) were detected in MLH1 carriers. The majority (13 of 21) of malignant tumours occurred in organs for which there is no recommended surveillance, and were lethal in three patients.     

Mutations associated with succinate dehydrogenase D-related malignant paragangliomas

Objective Hereditary paraganglioma (PGL) syndromes result from germline mutations in genes encoding subunits B, C and D of the mitochondrial enzyme succinate dehydrogenase (SDHB, SDHC and SDHD). SDHB‐related PGLs are known in particular for their high malignant potential. Recently, however, malignant PGLs were also reported among a small minority of Dutch carriers of the SDHD founder mutation D92Y. The aim of the study was to investigate which SDHD mutations are associated with malignant PGL. Design Case histories; collaborative study between referral centres in France, the USA, and the Netherlands. Patients Six unrelated patients with metastatic PGLs of either sympathetic or parasympathetic origin. Measurements Assessment of SDHD mutations underlying malignant PGL. Results Germline SDHD mutations underlying metastatic PGL were G148D, Y114X, L85X, W43X, D92Y, and IVS2+5G→A. Conclusion Our findings indicate that malignant SDHD‐related PGL is associated with several mutations besides D92Y.     

Mutations in SDHD are the major determinants of the clinical characteristics of Dutch head and neck paraganglioma patients

Objective Head and neck paragangliomas (HNPGL) are associated with mutations in genes encoding subunits of succinate dehydrogenase (SDH). The aim of this study was to evaluate SDH mutations, family history and phenotypes of patients with HNPGL in the Netherlands. Design We evaluated the clinical data and the mutation status of 236 patients referred between 1950 and 2009 to Leiden University Medical Center. Results The large majority of the patients carried mutations in SDHD (83%), and the p.Asp92Tyr Dutch founder mutation in SDHD alone accounted for 72% of all patients with HNPGL. A mutation in SDHAF2 was found in 4%, mutations in SDHB in 3% and a mutation in SDHC was identified in a single patient (0·4%). Over 80% of patients presented with positive family history, of whom 99·5% carried a mutation in an SDH gene. SDH mutations were also found in 56% of isolated patients, chiefly in SDHD (46%), but also in SDHB (8%) and SDHC (2%). The clinical parameters of these different subgroups are discussed: including the age at diagnosis, associated pheochromocytomas, tumour multifocality and malignancy rate. Conclusion The majority of Dutch patients with HNPGL present with a positive family history, in contrast to other European countries. The clinical characteristics of patients with HNPGL are chiefly determined by founder mutations in SDHD, the major causative gene in both familial and isolated patients with HNPGL. The high frequency of founder mutations in SDHD suggests a higher absolute prevalence of paraganglioma syndrome in the Netherlands.     

Role of succinate dehydrogenase deficiency and oncometabolites in gastrointestinal stromal tumors

Gastrointestinal stromal tumors(GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. At the molecular level, GISTs can be categorized into two groups based on the causative oncogenic mutations. Approximately 85% of GISTs are caused by gain-of-function mutations in the tyrosine kinase receptor KIT or platelet-derived growth factor receptor alpha(PDGFRA). The remaining GISTs, referred to as wild-type(WT) GISTs, are often deficient in succinate dehydrogenase complex(SDH), a key metabolic enzyme complex in the tricarboxylic acid(TCA) cycle and electron transport chain. SDH deficiency leads to the accumulation of succinate, a metabolite produced by the TCA cycle. Succinate inhibits α-ketoglutarate-dependent dioxygenase family enzymes, which comprise approximately 60 members and regulate key aspects of tumorigenesis such as DNA and histone demethylation, hypoxia responses, and m6 A mRNA modification. For this reason, succinate and metabolites with similar structures, such as D-2-hydroxyglutarate and fumarate, are considered oncometabolites. In this article, we review recent advances in the understanding of how metabolic enzyme mutations and oncometabolites drive human cancer with an emphasis on SDH mutations and succinate in WT GISTs.     

Pancreatic paraganglioma diagnosed by endoscopic ultrasound-guided fine needle aspiration: A case report and review of literature

BACKGROUNDPancreatic paragangliomas (PPGL) are rare benign neuroendocrine neoplasms but malignancy can occur. PPGL are often misdiagnosed as pancreatic neuroendocrine tumor or pancreatic adenocarcinoma.CASE SUMMARYWe reviewed 47 case reports of PPGL published in PubMed to date. Fifteen patients (15/47) with PPGL underwent endoscopic ultrasound-guided fine needle aspiration (EUS-FNA). Only six (6/15) were correctly diagnosed as PPGL. All patients with PPGL underwent surgical resection except three (one patient surgery was aborted because of hypertensive crisis, two patients had metastasis or involvement of major vessels). Our patient remained on close surveillance as she was asymptomatic.CONCLUSIONAccurate preoperative diagnosis of PPGL can be safely achieved by EUS-FNA with immunohistochemistry. Multidisciplinary team approach should be considered to bring the optimal results in the management of PPGL.     

Genetics of parathyroid tumours

Primary hyperparathyroidism (PHPT), due to parathyroid tumours, may occur as part of a complex syndrome or as an isolated (nonsyndromic) disorder, and both forms can occur as familial (i.e. hereditary) or nonfamilial (i.e. sporadic) disease. Syndromic PHPT includes multiple endocrine neoplasia (MEN) types 1 to 4 (MEN1 to MEN4) and the hyperparathyroidism‐jaw tumour (HPT‐JT) syndrome. Syndromic and hereditary PHPT are often associated with multiple parathyroid tumours, in contrast to sporadic PHPT, in which single parathyroid adenomas are more common. In addition, parathyroid carcinomas may occur in ~15% of patients with the HPT‐JT syndrome. MEN1 is caused by abnormalities of the MEN1 gene which encodes a tumour suppressor; MEN2 and MEN3 are due to mutations of the rearranged during transfection (RET) proto‐oncogene, which encodes a tyrosine kinase receptor; MEN4 is due to mutations of a cyclin‐dependent kinase inhibitor (CDNK1B); and HPT‐JT is due to mutations of cell division cycle 73 (CDC73), which encodes parafibromin. Nonsyndromic PHPT, which may be hereditary and referred to as familial isolated hyperparathyroidism, may also be due to MEN1, CDC73 or calcium‐sensing receptor (CASR) mutations. In addition, ~10% of patients presenting below the age of 45 years with nonsyndromic, sporadic PHPT may have MEN1, CDC73 or CASR mutations, and overall more than 10% of patients with PHPT will have a mutation in one of 11 genes. Genetic testing is available and of value in the clinical setting, as it helps in making the correct diagnosis and planning the management of these complex disorders associated with parathyroid tumours.     

Clinical presentation and penetrance of pheochromocytoma/paraganglioma syndromes

CONTEXT: The identification of mutations in genes encoding peptides of succinate dehydrogenase (SDH) in pheochromocytoma/paraganglioma syndromes has necessitated clear elucidation of genotype-phenotype associations. OBJECTIVE: Our objective was to determine genotype-phenotype associations in a cohort of patients with pheochromocytoma/paraganglioma syndromes and succinate dehydrogenase subunit B (SDHB) or subunit D (SDHD) mutations. DESIGN, SETTING, AND PARTICIPANTS: The International SDH Consortium studied 116 individuals (83 affected and 33 clinically unaffected) from 62 families with pheochromocytoma/paraganglioma syndromes and SDHB or SDHD mutations. Clinical data were collected between August 2003 and September 2004 from tertiary referral centers in Australia, France, New Zealand, Germany, United States, Canada, and Scotland. MAIN OUTCOME MEASURES: Data were collected on patients with pheochromocytomas and/or paragangliomas with respect to onset of disease, diagnosis, genetic testing, surgery, pathology, and disease progression. Clinical features were evaluated for evidence of genotype-phenotype associations, and penetrance was determined. RESULTS: SDHB mutation carriers were more likely than SDHD mutation carriers to develop extraadrenal pheochromocytomas and malignant disease, whereas SDHD mutation carriers had a greater propensity to develop head and neck paragangliomas and multiple tumors. For the index cases, there was no difference between 43 SDHB and 19 SDHD mutation carriers in the time to first diagnosis (34 vs. 28 yr, respectively; P = 0.3). However, when all mutation carriers were included (n = 112), the estimated age-related penetrance was different for SDHB vs. SDHD mutation carriers (P = 0.008). CONCLUSIONS: For clinical follow-up, features of SDHB mutation-associated disease include a later age of onset, extraadrenal (abdominal or thoracic) tumors, and a higher rate of malignancy. In contrast, SDHD mutation carriers, in addition to head and neck paragangliomas, should be observed for multifocal tumors, infrequent malignancy, and the possibility of extraadrenal pheochromocytoma.     

Mitochondrial function and content in pheochromocytoma/paraganglioma of succinate dehydrogenase mutation carriers

To date, the consequences of succinate dehydrogenase (SDH) impairment on overall mitochondrial functions are still obscure. In this study, we evaluated SDH activity and expression and mitochondrial homeostasis in 57 tissue samples of pheochromocytoma (PHEO)/paraganglioma (PGL) obtained from patients genotyped for PHEO/PGL susceptibility genes. The resulted SDH activity and content always decreased in SDH-mutated tumors, in one out of two MAX-mutated patients and in four patients resulted wild type (wt) at genetic screening. All these four wt patients were further screened for large deletions in SDH genes, TMEM127 and MAX and resulted wt but two had somatic SDHD mutations. The RT-PCR in the MAX-mutated sample suggests that the decrease in SDH depends on complex instability and not on a reduced SDHB expression. SDH mutations neither alter citrate synthase (CS) activity nor the content of voltage-dependent anion channel (VDAC) while the expression of the mitochondrial complex IV (cytochrome c oxidase (COX)) was found extremely variable in all (mutated and wt) samples suggesting an impairment of mitochondrial cristae in these tumors. In conclusion, tumors from patients with germ line SDH mutations invariably show decreased enzymatic activity and content, but an SDH impairment may also depend on SDH somatic mutations or, seemingly, on MAX mutations. The impaired SDH activity in the two wt tissues suggests mutations in other still unknown susceptibility genes. Finally, the extreme variability in COX expression levels is yet to be explained and this strongly suggests to evaluate other mitochondrial features to better understand the mitochondrial role in the pathogenesis of these tumors.     

On the association of succinate dehydrogenase mutations with hereditary paraganglioma

Hereditary paraganglioma (PGL) is characterized by the development of slow-growing, highly vascularized tumors that can present either as hormonally silent head and neck tumors or as abdominal pheochromocytomas. PGL tumors are caused by germline inactivating heterozygous mutations in the SDHB, SDHC and SDHD genes, which encode three of the four subunits of succinate dehydrogenase (SDH; succinate:ubiquinone oxidoreductase; mitochondrial complex II). Here, potential mechanisms by which SDH mutations could lead to tumor development are discussed. Mechanisms that lead to variations in the prevalence, penetrance and expressivity of SDH subunit mutations remain to be clarified to improve the clinical management of PGL patients. Recently, germline mutations in the FH gene, the product of which (fumarate hydratase) catalyzes the conversion of fumarate to malate in the Krebs cycle, have been detected in a distinct hereditary tumor syndrome, which is characterized by uterine and skin leiomyomatosis and papillary renal cancer. Although the exact mechanisms of tumorigenesis in both disorders are unknown, SDH and FH could be involved in the control of cell proliferation under normal physiological conditions in the affected tissue types. Whereas SDH might be involved in hypoxic proliferation of paraganglia, FH might play an important role in the regulation of ammonium metabolism in smooth muscle cells.     

Investigation of chromosome X inactivation and clinical phenotypes in female carriers of DKC1 mutations

Dyskeratosis congenita (DC) is an inherited bone marrow failure and cancer susceptibility syndrome caused by germline mutations in telomere biology genes. Germline mutations in DKC1, which encodes the protein dyskerin, cause X‐linked recessive DC. Because of skewed X‐chromosome inactivation, female DKC1 mutation carriers do not typically develop clinical features of DC. This study evaluated female DKC1 mutation carriers with DC‐associated phenotypes to elucidate the molecular features of their mutations, in comparison with unaffected carriers and mutation‐negative female controls. All female DKC1 mutation carriers had normal leukocyte subset telomere lengths and similarly skewed X‐inactivation in multiple tissue types, regardless of phenotype. We observed dyskerin expression, telomerase RNA accumulation, and pseudouridylation present in all mutation carriers at levels comparable to healthy wild‐type controls. Our study suggests that mechanisms in addition to X chromosome inactivation, such as germline mosaicism or epigenetics, may contribute to DC‐like phenotypes present in female DKC1 mutation carriers. Future studies are warranted to understand the molecular mechanisms associated with the phenotypic variability in female DKC1 mutation carriers, and to identify those at risk of disease. Am. J. Hematol. 91:1215–1220, 2016. © 2016 Wiley Periodicals, Inc.     

Higher risk of phaeochromocytoma/paraganglioma (Phaeo‐Pgl) in SDHD than SDHB carriers: an Australian cohort study

Carriers of succinate dehydrogenase (SDHx) mutations are at risk of developing phaeochromocytomas, catecholamine secreting extra‐adrenal paragangliomas and non‐secretory head and neck paragangliomas and require lifelong surveillance. There is no current consensus on the optimal surveillance strategy. This study describes the outcomes of a cohort of 50 SDHx mutation carriers followed at a tertiary Australian hospital using a surveillance protocol involving annual clinical review with plasma/urine metanephrines and biennial magnetic resonance imaging from skull base to pelvis.     

嗜铬细胞瘤分子病因学研究进展

嗜铬细胞瘤/副神经节瘤(pheochromocytoma/paraganglioma, PPGL)是一种罕见的神经内分泌肿瘤,约40%的PPGL具有家族遗传性,其发病与已知致病基因的胚系突变相关。此外,肿瘤的体细胞基因突变、拷贝数变异、甲基化程度和非编码RNA也参与PPGL的发生。全面和深入了解PPGL的发病机制,将为...     

Identification of steroid biosynthetic defects in genotype‐proven heterozygous individuals for 17α‐hydroxylase/17,20‐lyase deficiency

Objective P450c17 deficiency (17α‐hydroxylase/17,20‐lyase deficiency, 17OHD) is a rare form of congenital adrenal hyperplasia caused by CYP17A1 gene mutations. The D487_F489 deletion in exon 8 and Y329fs in exon 6 are relatively frequent mutations of the CYP17A1 gene in China that completely abolish the enzyme activity of P450c17. However, little remains known about steroid biosynthetic functions in carriers with these mutations in a single allele of the CYP17A1 gene, who are assumed to have 50% P450c17 activity. We investigated adrenal steroidogenic function in genotype‐proven heterozygotes carrying such mutations in the CYP17A1 gene in vivo. Patients and design Eight patients and fourteen family members from five families with 17OHD were recruited. The mutations of the CYP17A1 gene in these individuals were screened by sequencing. The hormonal response to cosyntropin (ACTH) was evaluated in the 14 genotype‐proven carriers and 45 age‐ and gender‐matched normal controls. Results Fourteen carriers of the CYP17A1 mutation – seven with the D487_F489 deletion, six with Y329fs and one with H373L – were identified from the five families with 17OHD. Compared with normal controls, carriers showed lower basal and ACTH‐stimulated cortisol levels but higher ACTH‐stimulated corticosterone levels. The ratios of corticosterone to cortisol in the genotype‐proven heterozygotes were higher than those of the normal controls at the baseline and after cosyntropin stimulation. Similarly, the progesterone levels and the ratios of progesterone to 17‐hydroxyprogesterone in the male heterozygotes were also higher than those of the normal controls, both before and after ACTH stimulation. Conclusion Genotype‐proven carriers of the CYP17A1 mutation who lack apparent clinical symptoms exhibit decreased adrenal 17α‐hydroxylase activity and altered adrenal gland reserve for steroid biosynthesis.