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

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

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

Mitochondrial disorders of the OXPHOS system

Mitochondrial disorders are among the most frequent inborn errors of metabolism, their primary cause being the dysfunction of the oxidative phosphorylation system (OXPHOS). OXPHOS is composed of the electron transport chain (ETC), formed by four multimeric enzymes and two mobile electron carriers, plus an ATP synthase [also called complex V (cV)]. The ETC performs the redox reactions involved in cellular respiration while generating the proton motive force used by cV to synthesize ATP. OXPHOS biogenesis involves multiple steps, starting from the expression of genes encoded in physically separated genomes, namely the mitochondrial and nuclear DNA, to the coordinated assembly of components and cofactors building each individual complex and eventually the supercomplexes. The genetic cause underlying around half of the diagnosed mitochondrial disease cases is currently known. Many of these cases result from pathogenic variants in genes encoding structural subunits or additional factors directly involved in the assembly of the ETC complexes. Here, we review the historical and most recent findings concerning the clinical phenotypes and the molecular pathological mechanisms underlying this particular group of disorders.

Mutational load in carotid body tumor

Background

Carotid body tumor (CBT) is a rare neoplasm arising from paraganglion located near the bifurcation of the carotid artery. There is great intra-tumor heterogeneity, and CBT development could be associated with both germline and somatic allelic variants. Studies on the molecular genetics of CBT are limited, and the molecular mechanisms of its pathogenesis are not fully understood. This work is focused on the estimation of mutational load (ML) in CBT.

Methods

Using the NextSeq 500 platform, we performed exome sequencing of tumors with matched lymph node tissues and peripheral blood obtained from six patients with CBT. To obtain reliable results in tumors with low ML, we developed and successfully applied a complex approach for the analysis of sequencing data. ML was evaluated as the number of somatic variants per megabase (Mb) of the target regions covered by the Illumina TruSeq Exome Library Prep Kit.

Results

The ML in CBT varied in the range of 0.09–0.28/Mb. Additionally, we identified several pathogenic/likely pathogenic somatic and germline allelic variants across six patients studied (including TP53 variants).

Conclusions

Using the developed approach, we estimated the ML in CBT, which is much lower than in common malignant tumors. Identified variants in known paraganglioma/pheochromocytoma-causative genes and novel genes could be associated with the pathogenesis of CBT. The obtained results expand our knowledge of the mutation process in CBT as well as the biology of tumor development.

Nonclonal Chromosomal Aberrations in Childhood Leukemia Survivors

BACKGROUND

Survivors of childhood cancer are at risk of developing a second malignancy. One possible mechanism for neoplastic transformation of cells is through induction of persistent genomic instability. This study aims to seek evidence of chromosomal instability in long-term childhood leukemia survivors (CLS) in one of the largest pediatric academic oncology centers in South East Asia.

METHODS

50 asymptomatic (subjects have remained leukemia-free since treatment cessation) CLS and 50 healthy controls were recruited in this cross-sectional study. Of 50 CLS, 44 had acute lymphoblastic leukemia and 6 had acute myeloid leukemia. G-banded karyotyping was performed on unstimulated peripheral blood leukocytes of all subjects.

RESULTS

CLS had significantly higher occurrence of karyotypic abnormalities compared to controls. Five CLS harbored six nonclonal abnormalities (mostly aneuploidy) while none were found in controls.

CONCLUSION

Subpopulations with nonclonal chromosomal aberrations were present in peripheral blood leukocytes of our cohort of childhood leukemia long-term survivors.

Loss of maternal chromosome 11 is a signature event in SDHAF2, SDHD, and VHL-related paragangliomas, but less significant in SDHB-related paragangliomas

Germline mutations in the succinate dehydrogenase (SDHA, SDHB, SDHC, SDHD, SDHAF2) or Von Hippel-Lindau (VHL) genes cause hereditary paraganglioma/pheochromocytoma. While SDHB (1p36) and VHL (3p25) are associated with autosomal dominant disease, SDHD (11q23) and SDHAF2 (11q13) show a remarkable parent-of-origin effect whereby tumor formation is almost completely dependent on paternal transmission of the mutant allele. Loss of the entire maternal copy of chromosome 11 occurs frequently in SDHD-linked tumors, and has been suggested to be the basis for this typical inheritance pattern.Using fluorescent in situ hybridization, microsatellite marker and SNP array analysis, we demonstrate that loss of the entire copy of chromosome 11 is also frequent in SDHAF2-related PGLs, occurring in 89% of tumors. Analysis of two imprinted differentially methylated regions (DMR) in 11p15, H19-DMR and KvDMR, showed that this loss always affected the maternal copy of chromosome 11. Likewise, loss of maternal chromosome 11p15 was demonstrated in 85% of SDHD and 75% of VHL-related PGLs/PCCs. By contrast, both copies of chromosome 11 were found to be retained in 62% of SDHB-mutated PGLs/PCCs, while only 31% showed loss of maternal chromosome 11p15. Genome-wide copy number analysis revealed frequent loss of 1p in SDHB mutant tumors and show greater genomic instability compared to SDHD and SDHAF2.These results show that loss of the entire copy of maternal chromosome 11 is a highly specific and statistically significant event in SDHAF2, SDHD and VHL-related PGLs/PCCs, but is less significant in SDHB-mutated tumors, suggesting that these tumors have a distinct genetic etiology.

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.

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

Background

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

Methods

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

Results

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

Conclusions

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

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.

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.

Recent advances in the genetics of SDH-related paraganglioma and pheochromocytoma

The last 10 years have seen enormous progress in the field of paraganglioma and pheochromocytoma genetics. The identification of the first gene related to paraganglioma, SDHD, encoding a subunit of mitochondrial succinate dehydrogenase (SDH), was quickly followed by the identification of mutations in SDHC and SDHB. Very recently several new SDH-related genes have been discovered. The SDHAF2 gene encodes an SDH co-factor related to the function of the SDHA subunit, and is currently exclusively associated with head and neck paragangliomas. SDHA itself has now also been identified as a paraganglioma gene, with the recent identification of the first mutation in a patient with extra-adrenal paraganglioma. Another SDH-related co-factor, SDHAF1, is not currently known to be a tumor suppressor, but may shed some light on the mechanisms of tumorigenesis. An entirely novel gene associated with adrenal pheochromocytoma, TMEM127, suggests that other new paraganglioma susceptibility genes may await discovery. In addition to these recent discoveries, new techniques related to mutation analysis, including genetic analysis algorithms, SDHB immunohistochemistry, and deletion analysis by MLPA have improved the efficiency and accuracy of genetic analysis. However, many intriguing questions remain, such as the striking differences in the clinical phenotype of genes that encode proteins with an apparently very close functional relationship, and the lack of expression of SDHD and SDHAF2 mutations when inherited via the maternal line. Little is still known of the origins and causes of truly sporadic tumors, and the role of oxygen in the relationships between high-altitude, familial and truly sporadic paragangliomas remains to be elucidated.

Common genetic mutations in the start codon of the SDH subunit D gene among Chinese families with familial head and neck paragangliomas

Head and neck paragangliomas (HNPGLs) are rare, and frequently associated with germline mutations of the succinate dehydrogenase (SDH) genes, especially for familial cases. The purpose of the study is to explore SDH mutations in Chinese families with familial HNPGLs in Taiwan. Four unrelated families with familial HNPGLs were screened for germline mutations in the SDHB, SDHC and SDHD genes by direct sequencing. One hundred healthy subjects without a diagnosis or family history of HNPGLs were screened as normal controls. Immunohistochemistry with SDHB antibody was performed for a carotid body tumor. Two allele variants were identified, including p.Met1Val (c.1A>G) in the SDHD gene in one family and p.Met1Ile (c.3G>C) in the SDHD gene in the other three families. Both variants are considered pathogenic because of the absence of these variants in 100 normal controls, 100% evolutionary conservation of the p.Met1 residue, co-segregation of the variants with the phenotype of HNPGL in pedigrees, and predicted abolishment of the translation start site. The tumor cells obtained from one proband harboring c.3G>C mis-sense mutation were weak diffuse staining in the cytoplasm of tumors cells. This study demonstrates that two mis-sense mutations at the start codon of the SDHD gene, including p.Met1Val (c.1A>G) and p.Met1Ile (c.3G>C), might be mutation hotspots in Chinese patients with familial HNPGLs.

Hereditäre Paragangliome

Hereditäre Paragangliome/Phäochromozytome werden autosomal-dominant vererbt. Es lassen sich 3 Formen, PGL1, PGL3 und PGL4 unterscheiden. Sie werden verursacht durch Mutationen in den Genen SDHD, SDHC und SDHB, welche für Komponenten des Komplexes II der mitochondrialen Atmungskette (Succinat-Ubiquinon-Reduktase, SDH) kodieren. Bei allen 3 Formen findet sich „loss of heterozygosity“ (LOH) der Region des mutierten Gens in Tumor-DNA. Dies führt zu Funktionsverlust der SDH, Anhäufung von Succinat sowie Sauerstoffradikalen. Dadurch werden hypoxieabhängige Stoffwechselwege aktiviert, welche zur Tumorbildung führen könnten. Während PGL3 und PGL4 sowohl durch maternal als auch durch paternal vererbte Keimbahnmutationen der Gene SDHC bzw. SDHB verursacht werden, findet sich PGL1 fast ausschließlich bei paternaler Transmission des mutierten SDHD-Gens. Diese Beobachtung lässt sich erklären durch partielle Inaktivierung (Imprinting) des maternalen SDHD-Gens und Induktion hypoxieabhängiger Gene in Paragangliengewebe, wodurch der Verlust des gesamten maternalen Chromosoms 11 durch Non-Disjunction begünstigt werden könnte.

Sdhd and SDHD/H19 knockout mice do not develop paraganglioma or pheochromocytoma

Background

Mitochondrial succinate dehydrogenase (SDH) is a component of both the tricarboxylic acid cycle and the electron transport chain. Mutations of SDHD, the first protein of intermediary metabolism shown to be involved in tumorigenesis, lead to the human tumors paraganglioma (PGL) and pheochromocytoma (PC). SDHD is remarkable in showing an ‘imprinted’ tumor suppressor phenotype. Mutations of SDHD show a very high penetrance in man and we postulated that knockout of Sdhd would lead to the development of PGL/PC, probably in aged mice.

Methodology/Principal Findings

We generated a conventional knockout of Sdhd in the mouse, removing the entire third exon. We also crossed this mouse with a knockout of H19, a postulated imprinted modifier gene of Sdhd tumorigenesis, to evaluate if loss of these genes together would lead to the initiation or enhancement of tumor development. Homozygous knockout of Sdhd results in embryonic lethality. No paraganglioma or other tumor development was seen in Sdhd KO mice followed for their entire lifespan, in sharp contrast to the highly penetrant phenotype in humans. Heterozygous Sdhd KO mice did not show hyperplasia of paraganglioma-related tissues such as the carotid body or of the adrenal medulla, or any genotype-related pathology, with similar body and organ weights to wildtype mice. A cohort of Sdhd/H19 KO mice developed several cases of profound cardiac hypertrophy, but showed no evidence of PGL/PC.

Conclusions

Knockout of Sdhd in the mouse does not result in a disease phenotype. H19 may not be an initiator of PGL/PC tumorigenesis.

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.

Chromosomal changes in sporadic and familial head and neck paragangliomas

Objective: Paragangliomas (PGLs) of the head and neck are benign neoplasms derived from the autonomic nervous system. Familial PGLs have been associated with germline mutations in succinate dehydrogenase (SDH) genes, and occasionally in Von Hippel–Lindau (VHL) and RET. The aim of this study was to compare somatic DNA copy number changes in tumors of familial and sporadic origin.

Material and Methods: Eight familial and 16 sporadic patients were analyzed for germline mutations and exon deletions in SDHB, SDHC, SDHD, VHL, and RET by direct sequencing and MLPA. Microarray CGH analysis was applied to map genome-wide somatic copy number changes.

Results: Fifteen cases carried a germline mutation in SDHB or SDHD, four of which not described before. Microarray CGH detected abnormalities in 10 of 18 cases, most frequently concerning deletions at 1p, 1q, and 11q, the sites where SDH are located. However, these deletions occurred in both SDH mutation–positive and SDH mutation–negative cases.

Conclusions: These data suggest that inactivating germline SDH mutations and somatic deletions of SDH genes as a “second hit” are involved in a subset, but not in all PGLs. Additional genes and mechanisms may need to be studied, especially in the group of sporadic PGL showing no chromosomal aberrations.

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.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Paraganglioma after maternal transmission of a succinate dehydrogenase gene mutation

CONTEXT

Inactivating mutations of SDHD, which is mapped to 11q23 and encodes the cybS subunit of succinate dehydrogenase, predispose to hereditary paraganglioma (PGL) and/or pheochromocytoma. So far no disease was shown to occur in case of maternal transmission of a SDHD mutation, suggesting the existence of genomic imprinting. A hypothetic model, involving the loss of the maternal copy of a tumor suppressor gene mapped to 11p15 in the tumoral tissue, has been proposed to explain this mode of inheritance.

OBJECTIVE

Our objective was to investigate the possibility of maternal transmission of SDHD-linked PGL.

DESIGN

A three-generation family carrying the SDHD W43X mutation was studied at the clinical, pathological, and genetical levels.

RESULTS

The germline's mutation was probably inherited from the grandfather. In the second generation, three carriers (two females and one male), who had the same at risk 11q13-q23 haplotype, developed multiple cervical PGLs. In the third generation, one boy received the mutation from his mother and developed a glomus tympanicum PGL at 11 yr. He shared only the 11q23 haplotype with the other affected members of the family. Methylation analysis of the differentially methylated region upstream of the maternally expressed H19 gene, mapped to 11p15, showed that the seventh CTCF binding site is hypermethylated in the germline of the affected boy suggesting a gain of imprinting.

CONCLUSION

Our data show that maternal transmission of a SDHD-linked PGL, even if a rare event, can occur. Therefore, we propose that children who inherited a pathogenic mutation from their mother should be considered as at risk of PGL.

Large proportion of low frequency microsatellite-instability and loss of heterozygosity in pheochromocytoma and endocrine tumors detected with an extended marker panel

PURPOSE

Pheochromocytoma (PCC) is a usually benign tumor originated in the majority of patients from the adrenal medulla. Regarding sporadic forms of PCC, mechanisms of pathogenesis are largely unknown. Recently, microsatellite-instability (MSI) was discussed as genetic factor contributing to PCC development. Since microsatellite markers used for MSI detection have only been recommended for colorectal carcinoma (CRC), we established an extended marker set for MSI detection in PCC.

METHODS

Twenty-two PCC patients were analyzed applying 11 microsatellite markers. Our marker set comprised the reference panel for CRC and six additional markers, which have already been described to detect MSI in tumors other than CRC. Moreover, 23 endocrine tumors with gastrointestinal origin were examined in order to test the applicability of this marker panel.

RESULTS

Microsatellite-instability was detected in 41% of PCCs. Twenty-seven percent showed loss of heterozygosity (LOH) events affecting different chromosomal regions. Among the 23 patients with endocrine tumors, only three (one pancreatic endocrine tumor, one duodenal neuro-endocrine tumor, one hepatic metastasis of a primary tumor with unknown origin) demonstrated MSI.

CONCLUSIONS

The extended microsatellite panel is qualified to detect MSI in PCC. Nine percent of MSI-positive cases would have not been noticed by the use of the reference panel alone. PCCs are characterized by low frequency MSI pointing to failures in factors involved in DNA replication.

Novel SDHD germ-line mutations in pheochromocytoma patients

BACKGROUND

SDHD germ-line mutations predispose to pheochromocytoma (PCC) and paraganglioma (PGL).

MATERIAL AND METHODS

The incidence and types of SDHD germ-line mutations are determined in 70 patients with apparently sporadic adrenal and extra-adrenal PCC.

RESULTS

SDHD sequence variants were identified in the germ line of five patients. Two of three novel mutations were in exon 1 and one in exon 3. One patient had a codon 1 missense mutation (M1K) and a concurrent 3-bp deletion in intron 1. Three of 10 family members had only the exon 1 mutation, whereas one had only the intron 1 mutation. The other exon 1 mutation resulted from a deletion of nucleotides 28-33 with a 12-bp in-frame insertion (c.28_33 del ins TAGGAGGCCCTA). This mutation generated a premature stop codon after codon 9 and was also present in the brother who had a bilateral PCC. The third patient with a carotid body tumour, with an abdominal and a thoracic PGL had a 12-bp deletion in exon 3 (codons 91-94, c.271_282 del). Her father carried the same mutation and had bilateral carotid body tumours. Two further patients, one with six PGL, carried a previously described H50R polymorphism, whose disease-specific relevance is currently unclear. The three patients with bona fide SDHD mutations were younger than those without germ-line mutations.

CONCLUSION

SDHD germ-line mutations are rare in patients with PCC, but their identification is an important prerequisite for the clinical care and appropriate management of affected individuals and their families.

Cervical paraganglioma--a case report and review of all cases reported to the Manchester Children's Tumour Registry 1954-2004

We report a 6-year-old male with left-sided ptosis, aniscoria and an initially missed slow growing left-sided neck mass, which was surgically excised when he was 9 years old and confirmed to be a paraganglioma. Seven years later he developed recurrent symptoms and was found to have a recurrence in the anterior mediastinum. We also report on all cases of cervical paragangliomas registered with the Manchester Children's Tumour Registry (MCTR) for the 50-year period 1954-2004. Paragangliomas are very rare tumours in the head and neck but should be considered in the differential diagnosis of neck masses especially when presenting with Horner syndrome. Recurrent symptoms and signs of hypertension herald recurrence. As these tumours can form part of a familial syndrome, long-term follow-up is necessary. Family members should be screened for early detection.

LOH on chromosome 11q, but not SDHD and Men1 mutations was frequently detectable in Chinese patients with pheochromocytoma and paraganglioma

Recently, the succinate dehydrogenase subunit D (SDHD) gene has been reported as one of the major susceptibility genes for pheochromocytoma (PCC) and paraganglioma (PGL). In addition, loss of heterozygosity (LOH) on chromosome 11, mainly in 11q23 and 11q13, is observed frequently in PGL. Based on the fact that mutation frequency of the SDHD gene is less than that of allelic loss at chromosome11q, where the SDHD gene is located, this region may contain other candidate tumor-suppressor genes involved in pathogenesis of PCC/PGL. The tumor-suppressor gene Men1 located in 11q13 is responsible for multiple endocrine neoplasia type 1 (Men1). However, the involvement of the Men1 gene in tumorigenesis of sporadic PCC/PGL is yet to be determined. To understand the roles of the two tumor-suppressor genes and LOH on chromosome 11q in Chinese patients with sporadic PCC or PGL, we performed mutation detection of the SDHD and Men1 genes in tumors from 35 Chinese patients with PCC/PGL; we also did LOH analysis at chromosome 11q for 25 patients out of the 35. No mutation was found in all of 35 patients. However, LOH was detected at one or more loci in 11 of the 25 (44%) tumor samples. The highest frequency of LOH occurred at D11S2006 (41%). Our results suggested that mutation in SDHD or Men1 gene was not found in Chinese patients with sporadic PCC/PGL. However the loss of chromosome 11q might be critical in development of PCC or PGL.

Characteristic genomic imbalances in pediatric pheochromocytoma

Pheochromocytoma (PCC) in children is rare, genetically not well described, and often related to a poor prognosis. We detected genomic imbalances in all 14 tumors from children analyzed by comparative genomic hybridization. A combinatorial loss of chromatin from 3p and 11p was a common feature in 10 of 14 (72%) patients, which was a result of either a loss of a total chromosome 3 and a total chromosome 11 in 6 of 10 patients, or confined deletions of their p arms in 4 of 10 patients. All patients exhibiting a loss of 3p and 11p carried VHL mutations. The VHL mutations were constitutive in 9 cases and somatic and restricted to tumor DNA in the remaining tumor. On the other hand, VHL mutations were absent in 4 patients, 2 who had other familial syndromes (NF1, SDHD) and 2 with unknown etiology. Our data show that the pattern of imbalances in the tumor DNA of PCC patients strongly correlated with an underlying familial VHL mutation. Furthermore, we show that true sporadic PCC is rare in childhood. Thus, children with PCC should be checked for a related predisposing gene. This would also identify familial syndrome patients requiring long-term monitoring for other syndrome-related malignancies.