SDHB variant type impacts phenotype and malignancy in pheochromocytoma-paraganglioma.

BACKGROUND: Traditional genotype-phenotype correlations for the succinate dehydrogenase-complex II (SDH) genes link SDHB variants to thoracic-abdominal pheochromocytoma-paraganglioma (PPGL) and SDHD variants to head and neck paraganglioma (HNPGL). However, in a recent study we found strong and specific genotype-phenotype associations for SDHD variants. In the present study we zoom in on the genotype-phenotype associations of SDHB gene variants, considering the impact of individual gene variants on disease risk and risk of malignancy. METHODS: We analysed two large independent data sets, including a total of 448 patients with PPGL and HNPGL, and studied the association of missense or truncating SDHB variants with tumour incidence, age of onset and malignancy risk using binomial testing and Kaplan-Meier analysis. RESULTS: Compared with missense variants, truncating SDHB variants were significantly and consistently more common in patients with PPGL, by a 20 percentage point margin. Malignancy was also significantly more common in truncating versus missense variant carriers. No overall differences in age of PPGL onset were noted between carriers of the two variant types, although some individual variants may differ in certain cases. Missense variants were marginally over-represented among patients with HNPGL, but the difference was not statistically significant. CONCLUSION: SDHB truncating variants convey an elevated risk for development of both PPGL and malignancy compared with missense variants. These results further support earlier robust associations between truncating variants and PPGL, and also suggest that the two variant types differ in their impact on complex II function, with PPGL/HNPGL tissues displaying differing sensitivities to changes in complex II function.

International initiative for a curated SDHB variant database improving the diagnosis of hereditary paraganglioma and pheochromocytoma.

BACKGROUND: SDHB is one of the major genes predisposing to paraganglioma/pheochromocytoma (PPGL). Identifying pathogenic SDHB variants in patients with PPGL is essential to the management of patients and relatives due to the increased risk of recurrences, metastases and the emergence of non-PPGL tumours. In this context, the 'NGS and PPGL (NGSnPPGL) Study Group' initiated an international effort to collect, annotate and classify SDHB variants and to provide an accurate, expert-curated and freely available SDHB variant database. METHODS: A total of 223 distinct SDHB variants from 737 patients were collected worldwide. Using multiple criteria, each variant was first classified according to a 5-tier grouping based on American College of Medical Genetics and NGSnPPGL standardised recommendations and was then manually reviewed by a panel of experts in the field. RESULTS: This multistep process resulted in 23 benign/likely benign, 149 pathogenic/likely pathogenic variants and 51 variants of unknown significance (VUS). Expert curation reduced by half the number of variants initially classified as VUS. Variant classifications are publicly accessible via the Leiden Open Variation Database system (https://databases.lovd.nl/shared/genes/SDHB). CONCLUSION: This international initiative by a panel of experts allowed us to establish a consensus classification for 223 SDHB variants that should be used as a routine tool by geneticists in charge of PPGL laboratory diagnosis. This accurate classification of SDHB genetic variants will help to clarify the diagnosis of hereditary PPGL and to improve the clinical care of patients and relatives with PPGL.

Variant type is associated with disease characteristics in SDHB, SDHC and SDHD-linked phaeochromocytoma-paraganglioma.

BACKGROUND: Pathogenic germline variants in subunits of succinate dehydrogenase (SDHB, SDHC and SDHD) are broadly associated with disease subtypes of phaeochromocytoma-paraganglioma (PPGL) syndrome. Our objective was to investigate the role of variant type (ie, missense vs truncating) in determining tumour phenotype. METHODS: Three independent datasets comprising 950 PPGL and head and neck paraganglioma (HNPGL) patients were analysed for associations of variant type with tumour type and age-related tumour risk. All patients were carriers of pathogenic germline variants in the SDHB, SDHC or SDHD genes. RESULTS: Truncating SDH variants were significantly over-represented in clinical cases compared with missense variants, and carriers of SDHD truncating variants had a significantly higher risk for PPGL (p<0.001), an earlier age of diagnosis (p<0.0001) and a greater risk for PPGL/HNPGL comorbidity compared with carriers of missense variants. Carriers of SDHB truncating variants displayed a trend towards increased risk of PPGL, and all three SDH genes showed a trend towards over-representation of missense variants in HNPGL cases. Overall, variant types conferred PPGL risk in the (highest-to-lowest) sequence SDHB truncating, SDHB missense, SDHD truncating and SDHD missense, with the opposite pattern apparent for HNPGL (p<0.001). CONCLUSIONS: SDHD truncating variants represent a distinct group, with a clinical phenotype reminiscent of but not identical to SDHB. We propose that surveillance and counselling of carriers of SDHD should be tailored by variant type. The clinical impact of truncating SDHx variants is distinct from missense variants and suggests that residual SDH protein subunit function determines risk and site of disease.

Parent-of-origin tumourigenesis is mediated by an essential imprinted modifier in SDHD-linked paragangliomas: SLC22A18 and CDKN1C are candidate tumour modifiers.

Mutations in SDHD and SDHAF2 (both located on chromosome 11) give rise to hereditary paraganglioma almost exclusively after paternal transmission of the mutation, and tumours often show loss of the entire maternal copy of chromosome 11. The 'Hensen' model postulates that a tumour modifier gene located on chromosome 11p15, a region known to harbour a cluster of imprinted genes, is essential to tumour formation. We observed decreased protein expression of the 11p15 candidate genes CDKN1C, SLC22A18 and ZNF215 evaluated in 60 SDHD-mutated tumours compared to normal carotid body tissue and non-SDH mutant tumours.We then created stable knockdown in vitro models, reasoning that the simultaneous knockdown of SDHD and a maternally expressed 11p15 modifier gene would enhance paraganglioma-related cellular characteristics compared to SDHD knockdown alone. Knockdown of SDHD in SNB19 and SHSY5Y cells resulted in the accumulation of succinate, the stabilization of HIF1 protein and a reduction in cell proliferation.Compared to single knockdown of SDHD, knockdown of SDHD together with SLC22A18 or with CDKN1C led to small but significant increases in cell proliferation and resistance to apoptosis, and to a gene expression profile closely related to the known transcriptional profile of SDH-deficient tumours. Of the 60 SDHD tumours investigated, four tumours showing retention of chromosome 11 showed SLC22A18 and CDKN1C expression levels comparable to levels in tumours showing loss of chromosome 11, suggesting loss of protein expression despite chromosomal retention.Our data strongly suggest that SLC22A18 and/or CDKN1C are tumour modifier genes involved in the tumourigenesis of SDHD-linked paraganglioma.

Models of parent-of-origin tumorigenesis in hereditary paraganglioma.

Paraganglioma and pheochromocytoma are neuroendocrine tumors that originate from either the sympathetic or the parasympathetic branches of the autonomic nervous system. Although 14 different genes have been linked to paraganglioma/pheochromocytoma, a subgroup of these genes is associated with hereditary paraganglioma-pheochromocytoma, the genes related to mitochondrial succinate dehydrogenase (SDH) including SDHA, SDHB, SDHC, SDHD and the assembly factor SDHAF2. Unlike mutations in other SDH subunit genes, mutations in SDHD and SDHAF2 show a remarkable parent-of-origin dependent tumorigenesis in which tumor formation almost exclusively occurs following paternal transmission of the mutation. To date, three different models have sought to explain the striking inheritance pattern seen in SDHD and SDHAF2-linked families. Despite the fact that the models suffer to varying degrees from a lack of experimental verification, all three models have made some attempt to incorporate current data and understanding of this phenomenon. In this review, we discuss our present understanding of this phenomenon and describe the three models that seek to explain the inheritance pattern in SDHD and SDHAF2-linked families.

The role of complex II in disease.

Genetically defined mitochondrial deficiencies that result in the loss of complex II function lead to a range of clinical conditions. An array of tumor syndromes caused by complex II-associated gene mutations, in both succinate dehydrogenase and associated accessory factor genes (SDHA, SDHB, SDHC, SDHD, SDHAF1, SDHAF2), have been identified over the last 12 years and include hereditary paraganglioma-pheochromocytomas, a diverse group of renal cell carcinomas, and a specific subtype of gastrointestinal stromal tumors (GIST). In addition, congenital complex II deficiencies due to inherited homozygous mutations of the catalytic components of complex II (SDHA and SDHB) and the SDHAF1 assembly factor lead to childhood disease including Leigh syndrome, cardiomyopathy and infantile leukodystrophies. The role of complex II subunit gene mutations in tumorigenesis has been the subject of intensive research and these data have led to a variety of compelling hypotheses. Among the most widely researched are the stabilization of hypoxia inducible factor 1 under normoxia, and the generation of reactive oxygen species due to defective succinate:ubiquinone oxidoreductase function. Further progress in understanding the role of complex II in disease, and in the development of new therapeutic approaches, is now being hampered by the lack of relevant cell and animal models. This article is part of a Special Issue entitled: Respiratory complex II: Role in cellular physiology and disease.

Paraganglioma and pheochromocytoma upon maternal transmission of SDHD mutations.

BACKGROUND: The SDHD gene encodes a subunit of the mitochondrial tricarboxylic acid cycle enzyme and tumor suppressor, succinate dehydrogenase. Mutations in this gene show a remarkable pattern of parent-of-origin related tumorigenesis, with almost all SDHD-related cases of head and neck paragangliomas and pheochromocytomas attributable to paternally-transmitted mutations. METHODS: Here we explore the underlying molecular basis of three cases of paraganglioma or pheochromocytoma that came to our attention due to apparent maternal transmission of an SDHD mutation. We used DNA analysis of family members to establish the mode of inheritance of each mutation. Genetic and immunohistochemical studies of available tumors were then carried out to confirm SDHD-related tumorigenesis. RESULTS: We found convincing genetic and immunohistochemical evidence for the maternally-related occurrence of a case of pheochromocytoma, and suggestive evidence in a case of jugular paraganglioma. The third case appears to be a phenocopy, a sporadic paraganglioma in an SDHD mutation carrier with no immunohistochemical or DNA evidence to support a causal link between the mutation and the tumor. Microsatellite analysis in the tumor of patient 1 provided evidence for somatic recombination and loss of the paternal region of chromosome 11 including SDHD and the maternal chromosome including the centromere and the p arm. CONCLUSIONS: Transmission of SDHD mutations via the maternal line can, in rare cases, result in tumorigenesis. Despite this finding, the overwhelming majority of carriers of maternally-transmitted mutations will remain tumor-free throughout life.

SDHAF2-Linked Metastatic Paraganglioma: A Case Report with Implications for Counseling and Follow-Up of Pathogenic SDHAF2 Variant Carriers.

Head and neck paragangliomas are slow growing and highly vascular neuroendocrine tumors. It is currently assumed that SDHAF2 variants exclusively cause benign and often multicentric head and neck paragangliomas. Here, we present a patient diagnosed with multiple SDHAF2-linked head and neck paragangliomas who in addition developed paraganglioma metastases to the lung and spine and a primary or metastatic paraganglioma in the head of the pancreas. During the course of the disease, a range of management strategies were deployed for the different head and neck tumors, including total resections, partial resections, and active surveillance. After identification of the paraganglioma metastases, the patient was treated with lanreotide after which the disease remained stable during the 27 months of follow-up.

The Warburg effect in 2012.

PURPOSE OF REVIEW: A revival of interest in tumor metabolism is underway and here we discuss recent results with a focus on the central theme of the Warburg effect, aerobic glycolysis. RECENT FINDINGS: The M2 tumor-specific isoform of pyruvate kinase has generated much interest, but it has now been reported that PKM2 is not specific to tumors. Despite this setback, the reciprocal regulation of PKM2, prolyl hydroxylase 3 and HIF-1 in a positive feedback loop shows that PKM2 is important to tumor metabolism. Hexokinase II was reported to be a crucial regulator of glycolysis in glioblastoma multiforme, and the importance of lactate dehydrogenase was underlined by evidence that a 'lactate-based dialog' exists between cancer cells and endothelial cells. A growing appreciation of the role of oncogenes and tumor suppressor genes in the Warburg effect was reflected in reports of the regulation of glutamine metabolism by p53, the role of c-Myc in the high glucose uptake of tumors, and the regulation of ectonucleoside triphosphate diphosphohydrolase 5 (ENTPD5) and ATP consumption by AKT. The sirtuins, SIRT3 and SIRT6, were also shown to play central roles in aerobic glycolysis and other aspects of tumor metabolism. SUMMARY: The results discussed illustrate the growing integration of the previously distinct fields of molecular biological and metabolic cancer research and show that this synergy is beginning to yield a more complete and comprehensive understanding of the tumor cell.

Hypothesis: Why Different Types of SDH Gene Variants Cause Divergent Tumor Phenotypes.

Despite two decades of paraganglioma-pheochromocytoma research, the fundamental question of how the different succinate dehydrogenase (SDH)-related tumor phenotypes are initiated has remained unanswered. Here, we discuss two possible scenarios by which missense (hypomorphic alleles) or truncating (null alleles) SDH gene variants determine clinical phenotype. Dysfunctional SDH is a major source of reactive oxygen species (ROS) but ROS are inhibited by rising succinate levels. In scenario 1, we propose that SDH missense variants disrupt electron flow, causing elevated ROS levels that are toxic in sympathetic PPGL precursor cells but well controlled in oxygen-sensing parasympathetic paraganglion cells. We also suggest that SDHAF2 variants, solely associated with HNPGL, may cause the reversal of succinate dehydrogenase to fumarate reductase, producing very high ROS levels. In scenario 2, we propose a modified succinate threshold model of tumor initiation. Truncating SDH variants cause high succinate accumulation and likely initiate tumorigenesis via disruption of 2-oxoglutarate-dependent enzymes in both PPGL and HNPGL precursor tissues. We propose that missense variants (including SDHAF2) cause lower succinate accumulation and thus initiate tumorigenesis only in very metabolically active tissues such as parasympathetic paraganglia, which naturally show very high levels of succinate.

Long-term in vitro 2D-culture of SDHB and SDHD-related human paragangliomas and pheochromocytomas.

The neuroendocrine tumours paraganglioma and pheochromocytoma (PPGLs) are commonly associated with succinate dehydrogenase (SDH) gene variants, but no human SDH-related PPGL-derived cell line has been developed to date. The aim of this study was to systematically explore practical issues related to the classical 2D-culture of SDH-related human paragangliomas and pheochromocytomas, with the ultimate goal of identifying a viable tumour-derived cell line. PPGL tumour tissue/cells (chromaffin cells) were cultured in a variety of media formulations and supplements. Tumour explants and dissociated primary tumour cells were cultured and stained with a range of antibodies to identify markers suitable for use in human PPGL culture. We cultured 62 PPGLs, including tumours with confirmed SDHB, SDHC and SDHD variants, as well as several metastatic tumours. Testing a wide range of basic cell culture media and supplements, we noted a marked decline in chromaffin cell numbers over a 4-8 week period but the persistence of small numbers of synaptophysin/tyrosine hydroxylase-positive chromaffin cells for up to 99 weeks. In cell culture, immunohistochemical staining for chromogranin A and neuron-specific enolase was generally negative in chromaffin cells, while staining for synaptophysin and tyrosine hydroxylase was generally positive. GFAP showed the most consistent staining of type II sustentacular cells. Of the media tested, low serum or serum-free media best sustained relative chromaffin cell numbers, while lactate enhanced the survival of synaptophysin-positive cells. Synaptophysin-positive PPGL tumour cells persist in culture for long periods but show little evidence of proliferation. Synaptophysin was the most consistent cell marker for chromaffin cells and GFAP the best marker for sustentacular cells in human PPGL cultures.

SDHAF2 mutations in familial and sporadic paraganglioma and phaeochromocytoma.

BACKGROUND: Paragangliomas and phaeochromocytomas are neuroendocrine tumours associated frequently with germline mutations of SDHD, SDHC, and SDHB. Previous studies have shown the imprinted SDHAF2 gene to be mutated in a large Dutch kindred with paragangliomas. We aimed to identify SDHAF2 mutation carriers, assess the clinical genetic significance of SDHAF2, and describe the associated clinical phenotype. METHODS: We undertook a multicentre study in Spain and The Netherlands in 443 apparently sporadic patients with paragangliomas and phaeochromocytomas who did not have mutations in SDHD, SDHC, or SDHB. We analysed DNA of 315 patients for germline mutations of SDHAF2; a subset (n=200) was investigated for gross gene deletions. DNA from a group of 128 tumours was studied for somatic mutations. We also examined a Spanish family with head and neck paragangliomas with a young age of onset for the presence of SDHAF2 mutations, undertook haplotype analysis in this kindred, and assessed their clinical phenotype. FINDINGS: We did not identify any germline or somatic mutations of SDHAF2, and no gross gene deletions were noted in the subset of apparently sporadic patients analysed. Investigation of the Spanish family identified a pathogenic germline DNA mutation of SDHAF2, 232G-->A (Gly78Arg), identical to the Dutch kindred. INTERPRETATION: SDHAF2 mutations do not have an important role in phaeochromocytoma and are rare in head and neck paraganglioma. Identification of a second family with the Gly78Arg mutation suggests that this is a crucial residue for the function of SDHAF2. We conclude that SDHAF2 mutation analysis is justified in very young patients with isolated head and neck paraganglioma without mutations in SDHD, SDHC, or SDHB, and in individuals with familial antecedents who are negative for mutations in all other risk genes. FUNDING: Dutch Cancer Society, European Union 6th Framework Program, Fondo Investigaciones Sanitarias, Fundación Mutua Madrileña, and Red Temática de Investigación Cooperativa en Cáncer.

Germline DLST Variants Promote Epigenetic Modifications in Pheochromocytoma-Paraganglioma.

CONTEXT: Pheochromocytomas and paragangliomas (PPGLs) are neuroendocrine tumors in which altered central metabolism appears to be a major driver of tumorigenesis, and many PPGL genes encode proteins involved in the tricarboxylic acid (TCA) cycle. OBJECTIVE/DESIGN: While about 40% of PPGL cases carry a variant in a known gene, many cases remain unexplained. In patients with unexplained PPGL showing clear evidence of a familial burden or multiple tumors, we aimed to identify causative factors using genetic analysis of patient DNA and functional analyses of identified DNA variants in patient tumor material and engineered cell lines. PATIENTS AND SETTING: Patients with a likely familial cancer burden of pheochromocytomas and/or paragangliomas and under investigation in a clinical genetic and clinical research setting in university hospitals. RESULTS: While investigating unexplained PPGL cases, we identified a novel variant, c.1151C>T, p.(Pro384Leu), in exon 14 of the gene encoding dihydrolipoamide S-succinyltransferase (DLST), a component of the multi-enzyme complex 2-oxoglutarate dehydrogenase. Targeted sequence analysis of further unexplained cases identified a patient carrying a tumor with compound heterozygous variants in DLST, consisting of a germline variant, c.1121G>A, p.(Gly374Glu), together with a somatic missense variant identified in tumor DNA, c.1147A>G, p.(Thr383Ala), both located in exon 14. Using a range of in silico and functional assays we show that these variants are predicted to be pathogenic, profoundly impact enzyme activity, and result in DNA hypermethylation. CONCLUSIONS: The identification and functional analysis of these DLST variants further validates DLST as an additional PPGL gene involved in the TCA cycle.

Low penetrance of a SDHB mutation in a large Dutch paraganglioma family.

BACKGROUND: Germline mutations of the succinate dehydrogenase subunit B gene (SDHB) predispose carriers for paragangliomas, and current estimates of the chance of mutation carriers actually developing tumors (penetrance) are high. We evaluate the phenotype and penetrance of a germline SDHB mutation in a large and clinically well-characterized paraganglioma family. METHODS: Following identification of the mutation in a 31 year old index-patient, extensive clinical screening was performed in mutation carriers to evaluate the presence of head and neck, thoracic and abdominal paragangliomas. Presymptomatic DNA testing was performed in 19 family members. RESULTS: DNA analysis detected 14 further SDHB mutation carriers. Three mutation carriers (median age 78 years) declined clinical surveillance, but had no clinical signs or symptoms associated with paragangliomas. The remaining 11 mutation carriers (mean age 53, range 37-76 years) consented to clinical screening. In only two, aged 43 and 48 years, were subclinical vagal paragangliomas identified. CONCLUSIONS: Only three of the fifteen mutation carriers in this family have developed paraganglioma, which results in a calculated penetrance of 26% at 48 years of age. This figure is lower than current estimates, and we conclude that the co-operation of this family allowed an almost complete attainment of mutation carriers, and the extensive clinical evaluation carried out allowed us to identify all affected individuals.

An immunohistochemical procedure to detect patients with paraganglioma and phaeochromocytoma with germline SDHB, SDHC, or SDHD gene mutations: a retrospective and prospective analysis.

BACKGROUND: Phaeochromocytomas and paragangliomas are neuro-endocrine tumours that occur sporadically and in several hereditary tumour syndromes, including the phaeochromocytoma-paraganglioma syndrome. This syndrome is caused by germline mutations in succinate dehydrogenase B (SDHB), C (SDHC), or D (SDHD) genes. Clinically, the phaeochromocytoma-paraganglioma syndrome is often unrecognised, although 10-30% of apparently sporadic phaeochromocytomas and paragangliomas harbour germline SDH-gene mutations. Despite these figures, the screening of phaeochromocytomas and paragangliomas for mutations in the SDH genes to detect phaeochromocytoma-paraganglioma syndrome is rarely done because of time and financial constraints. We investigated whether SDHB immunohistochemistry could effectively discriminate between SDH-related and non-SDH-related phaeochromocytomas and paragangliomas in large retrospective and prospective tumour series. METHODS: Immunohistochemistry for SDHB was done on 220 tumours. Two retrospective series of 175 phaeochromocytomas and paragangliomas with known germline mutation status for phaeochromocytoma-susceptibility or paraganglioma-susceptibility genes were investigated. Additionally, a prospective series of 45 phaeochromocytomas and paragangliomas was investigated for SDHB immunostaining followed by SDHB, SDHC, and SDHD mutation testing. FINDINGS: SDHB protein expression was absent in all 102 phaeochromocytomas and paragangliomas with an SDHB, SDHC, or SDHD mutation, but was present in all 65 paraganglionic tumours related to multiple endocrine neoplasia type 2, von Hippel-Lindau disease, and neurofibromatosis type 1. 47 (89%) of the 53 phaeochromocytomas and paragangliomas with no syndromic germline mutation showed SDHB expression. The sensitivity and specificity of the SDHB immunohistochemistry to detect the presence of an SDH mutation in the prospective series were 100% (95% CI 87-100) and 84% (60-97), respectively. INTERPRETATION: Phaeochromocytoma-paraganglioma syndrome can be diagnosed reliably by an immunohistochemical procedure. SDHB, SDHC, and SDHD germline mutation testing is indicated only in patients with SDHB-negative tumours. SDHB immunohistochemistry on phaeochromocytomas and paragangliomas could improve the diagnosis of phaeochromocytoma-paraganglioma syndrome. FUNDING: The Netherlands Organisation for Scientific Research, Dutch Cancer Society, Vanderes Foundation, Association pour la Recherche contre le Cancer, Institut National de la Santé et de la Recherche Médicale, and a PHRC grant COMETE 3 for the COMETE network.

Advances in paraganglioma-pheochromocytoma cell lines and xenografts.

This review describes human and rodent-derived cell lines and xenografts developed over the last five decades that are suitable or potentially suitable models for paraganglioma-pheochromocytoma research. We outline the strengths and weaknesses of various models and emphasize the recurring theme that, despite the major challenges involved, more effort is required in the search for valid human and animal cell models of paraganglioma-pheochromocytoma, particularly those relevant to cancers carrying a mutation in one of the succinate dehydrogenase genes. Despite many setbacks, the recent development of a potentially important new model, the RS0 cell line, gives reason for optimism regarding the future of models in the paraganglioma-pheochromocytoma field. We also note that classic approaches to cell line derivation such as SV40-mediated immortalization and newer approaches such as organoid culture or iPSCs have been insufficiently explored. As many existing cell lines have been poorly characterized, we provide recommendations for reporting of paraganglioma and pheochromocytoma cell lines, including the strong recommendation that cell lines are made widely available via the ATCC or a similar cell repository. Basic research in paraganglioma-pheochromocytoma is currently transitioning from the analysis of genetics to the analysis of disease mechanisms and the clinically exploitable vulnerabilities of tumors. A successful transition will require many more disease-relevant human and animal models to ensure continuing progress.

Inhibition of succinate dehydrogenase dysregulates histone modification in mammalian cells.

Remodelling of mitochondrial metabolism is a hallmark of cancer. Mutations in the genes encoding succinate dehydrogenase (SDH), a key Krebs cycle component, are associated with hereditary predisposition to pheochromocytoma and paraganglioma, through mechanisms which are largely unknown. Recently, the jumonji-domain histone demethylases have emerged as a novel family of 2-oxoglutarate-dependent chromatin modifiers with credible functions in tumourigenesis. Using pharmacological and siRNA methodologies we show that increased methylation of histone H3 is a general consequence of SDH loss-of-function in cultured mammalian cells and can be reversed by overexpression of the JMJD3 histone demethylase. ChIP analysis revealed that the core promoter of IGFBP7, which encodes a secreted protein upregulated after loss of SDHB, showed decreased occupancy by H3K27me3 in the absence of SDH. Finally, we provide the first evidence that the chief (type I) cell is the major methylated histone-immunoreactive constituent of paraganglioma. These results support the notion that loss of mitochondrial function alters epigenetic processes and might provide a signature methylation mark for paraganglioma.

The first Dutch SDHB founder deletion in paraganglioma-pheochromocytoma patients.

BACKGROUND: Germline mutations of the tumor suppressor genes SDHB, SDHC and SDHD play a major role in hereditary paraganglioma and pheochromocytoma. These three genes encode subunits of succinate dehydrogenase (SDH), the mitochondrial tricarboxylic acid cycle enzyme and complex II component of the electron transport chain. The majority of variants of the SDH genes are missense and nonsense mutations. To date few large deletions of the SDH genes have been described. METHODS: We carried out gene deletion scanning using MLPA in 126 patients negative for point mutations in the SDH genes. We then proceeded to the molecular characterization of deletions, mapping breakpoints in each patient and used haplotype analysis to determine whether the deletions are due to a mutation hotspot or if a common haplotype indicated a single founder mutation. RESULTS: A novel deletion of exon 3 of the SDHB gene was identified in nine apparently unrelated Dutch patients. An identical 7905 bp deletion, c.201-4429_287-933del, was found in all patients, resulting in a frameshift and a predicted truncated protein, p.Cys68HisfsX21. Haplotype analysis demonstrated a common haplotype at the SDHB locus. Index patients presented with pheochromocytoma, extra-adrenal PGL and HN-PGL. A lack of family history was seen in seven of the nine cases. CONCLUSION: The identical exon 3 deletions and common haplotype in nine patients indicates that this mutation is the first Dutch SDHB founder mutation. The predominantly non-familial presentation of these patients strongly suggests reduced penetrance. In this small series HN-PGL occurs as frequently as pheochromocytoma and extra-adrenal PGL.

Genome-wide linkage scan in Dutch hereditary non-BRCA1/2 breast cancer families identifies 9q21-22 as a putative breast cancer susceptibility locus.

Breast cancer accounts for over 20% of all female cancers. A positive family history remains one of the most important risk factors for the disease, with first-degree relatives of patients having a twofold elevated risk. Known breast cancer susceptibility genes such as BRCA1 and BRCA2 explain only 20-25% of this risk, suggesting the existence of other breast cancer susceptibility genes. Here, we report the results of a genome-wide linkage scan in 55 high-risk Dutch breast cancer families with no mutations in BRCA1 and BRCA2. Twenty-two of these families were also part of a previous linkage study by the Breast Cancer Linkage Consortium. In addition, we performed CGH analyses in 61 tumors of these families and 31 sporadic tumors. Three regions were identified with parametric HLOD scores >1, and three with nonparametric LOD scores >1.5. Upon further marker genotyping for the candidate loci, and the addition of another 30 families to the analysis, only the locus on chromosome 9 (9q21-22, marker D9S167) remained significant, with a nonparametric multipoint LOD score of 3.96 (parametric HLOD 0.56, alpha = 0.18). With CGH analyses we observed preferential copy number loss at BAC RP11-276H19, containing D9S167 in familial tumors as compared to sporadic tumors (P < 0.001). Five candidate genes were selected from the region around D9S167 and their coding regions subjected to direct sequence analysis in 16 probands. No clear pathogenic mutations were found in any of these genes.