Mutations in the SDHB gene are associated with extra-adrenal and/or malignant phaeochromocytomas

Germ-line mutations in the genes encoding succinate dehydrogenase complex subunits B (SDHB) and D (SDHD) have been reported in familial paragangliomas and apparently sporadic phaeochromocytomas (ASP), but the genotype-phenotype relationships of these mutations are unknown. Eighty-four patients (all but 2 followed up for 8.8 +/- 5.7 years) with ASP (57 with adrenal tumors, 27 with extra-adrenal, multiple, malignant, or recurrent tumors) were screened for the major susceptibility genes for phaeochromocytoma (RET, VHL, SDHD, and SDHB). Thirty-three tumors were available for molecular analysis, enzyme assays, and immunohistochemistry. No (0%) RET and 2 (2.4%) VHL mutations were detected. Only two coding single nucleotide polymorphisms in the SDHD gene (G12S and H50R) were found in 6 patients (7%). Conversely, six deleterious mutations in the SDHB gene were identified in 8 patients (9.5%). Ectopic site and recurrence or malignancy were strongly associated with SDHB mutations (7 of 8, 87%, versus 20 of 76, 26%; P = 0.001). Somatic DNA analysis indicated a loss of heterozygosity at chromosome 1p36 (SDHB locus) in 16 of 33 cases (48%). A loss of heterozygosity at the SDHB locus was found in all tumors with SDHB mutation, and assays of respiratory chain enzymes showed a complete loss of complex II catalytic activity. The vascular architecture of tumors with SDHB mutations displayed features typical of malignancy. These data strongly suggest that SDHB gene is a tumor suppressor gene and that the identification of germ-line mutations in SDHB gene in patients with ASPs should be considered as a high-risk factor for malignancy or recurrence.     

Investigation of the role of SDHB inactivation in sporadic phaeochromocytoma and neuroblastoma

Germline mutations in the succinate dehydrogenase (SDH) (mitochondrial respiratory chain complex II) subunit B gene, SDHB, cause susceptibility to head and neck paraganglioma and phaeochromocytoma. Previously, we did not identify somatic SDHB mutations in sporadic phaeochromocytoma, but SDHB maps to 1p36, a region of frequent loss of heterozygosity (LOH) in neuroblastoma as well. Hence, to evaluate SDHB as a candidate neuroblastoma tumour suppressor gene (TSG) we performed mutation analysis in 46 primary neuroblastomas by direct sequencing, but did not identify germline or somatic SDHB mutations. As TSGs such as RASSF1A are frequently inactivated by promoter region hypermethylation, we designed a methylation-sensitive PCR-based assay to detect SDHB promoter region methylation. In 21% of primary neuroblastomas and 32% of phaeochromocytomas (32%) methylated (and unmethylated) alleles were detected. Although promoter region methylation was also detected in two neuroblastoma cell lines, this was not associated with silencing of SDHB expression, and treatment with a demethylating agent (5-azacytidine) did not increase SDH activity. These findings suggest that although germline SDHB mutations are an important cause of phaeochromocytoma susceptibility, somatic inactivation of SDHB does not have a major role in sporadic neural crest tumours and SDHB is not the target of 1p36 allele loss in neuroblastoma and phaeochromocytoma.     

Germline SDHB mutations and familial renal cell carcinoma

Familial renal cell carcinoma (RCC) is a heterogeneous disorder that is most commonly caused by germline mutations in the VHL, MET, and FLCN genes or by constitutional chromosome 3 translocations. However, for many patients with familial RCC, the genetic basis of the disease is undefined. We investigated whether germline mutations in fumarate hydratase (FH) or succinate dehydrogenase subunit genes (SDHB, SDHC, SDHD) were associated with RCC susceptibility in 68 patients with no clinical evidence of an RCC susceptibility syndrome. No mutations in FH, SDHC, or SDHD were identified in probands, but 3 of the 68 (4.4%) probands had a germline SDHB mutation. Patients with a germline SDHB mutation presented with familial RCC (n = 1) or bilateral RCC (n = 2) and no personal or family history of pheochromocytoma or head and neck paraganglioma. Age at diagnosis of RCC in SDHB mutation carriers ranged from 24 to 73 years. These findings 1) demonstrate that patients with suspected inherited RCC should be examined for germline SDHB mutations, 2) suggest that all identified SDHB mutation carriers should be offered surveillance for RCC, and 3) provide a further link between familial RCC and activation of hypoxic-gene response pathways.     

Clinical characteristics of pheochromocytoma patients with germline mutations in SDHD.

PURPOSE: We examined the value of SDHD mutation screening in patients presenting with apparently sporadic and familial pheochromocytoma for the identification of SDHD-related pheochromocytomas. PATIENTS AND METHODS: This retrospective study involved 126 patients with adrenal or extra-adrenal pheochromocytomas, including 24 patients with a family history of multiple endocrine neoplasia 2, von Hippel-Lindau disease, neurofibromatosis type 1, or paraganglioma (PGL). Conformation-dependent gel electrophoresis and sequence determination analysis of germline and tumor DNA were used to identify SDHD alterations. The clinical and molecular characteristics of sporadic and hereditary tumors were compared. We reviewed the literature and compared our results with those from previously published studies. RESULTS: Pathogenic germline SDHD mutations were identified in three patients: two (2.0%) of the 102 apparently sporadic pheochromocytoma patients and one patient with a family history of PGL. These patients presented with multifocal disease (two of three multifocal patients) or with a single adrenal tumor (one of 82 patients). In the literature, mutations are mostly found in patients 相似文献   

Mutation analysis of the c-mos proto-oncogene and the endothelin-B receptor gene in medullary thyroid carcinoma and phaeochromocytoma.

The characteristic tumours of MEN 2 are medullary thyroid carcinoma (MTC) and phaeochromocytoma. Somatic RET mutations have been found in only 23-40% of sporadic MTC and 10% of sporadic phaeochromocytomas. Thus, we sought other genes which may play a role in the pathogenesis of these tumours. We carried out direct sequence analysis of human c-mos and human ENRB in a series of sporadic MTC and phaeochromocytomas to determine if somatic mutations in these two genes could account for some of the sporadic MEN 2-related tumours in which no RET mutations are detected. No somatic mutations were found.     

Absence of somatic SDHD mutations in sporadic neuroendocrine tumors and detection of two germline variants in paraganglioma patients

Allelic loss of the long arm of chromosome 11 is frequent in neuroendocrine tumors (NET) of different organs. However, the MEN1 gene on 11q13 is mutated only in a subset of NET and allelic losses on 11q frequently extend to the telomere. In this genetic region lies the tumor suppressor gene SDHD which is associated with hereditary paragangliomas (PGL1). We sought to determine whether SDHD plays a role in the development of sporadic NET. By mutation and deletion analysis of SDHD we were unable to detect any SDHD mutation in 45 NET of the lung, gastrointestinal tract, pancreas or parathyroid. However, we found allelic deletions in 20 to 50% of all tumors but parathyroid adenomas. Furthermore, we found heterozygous germline variants in 2/8 paragangliomas. A first case of variant c.149 A>G (H50R) was found in a patient with an extra-adrenal pheochromocytoma, the other variant c.34 G>A (G12S) in a patient with a paratracheal paraganglioma, C-cell hyperplasia of the thyroid and hyperplasia of ACTH-producing cells of the pituitary gland. Both variants were absent in 93 controls. Our results demonstrate that somatic SDHD mutations are rare in sporadic NET. However, LOH alone could lead to a complete loss of function since SDHD is an imprinted gene. Furthermore, we describe two germline variants possibly causing hereditary paragangliomas.     

家族性副神经节瘤中SDHD SDHB 基因突变分析

目的：探讨SDHD 、SDHB 基因突变在我国副神经节瘤（PGL ）患者中的发生状况,为PGL 分子诊断和分子遗传学的深入研究提供基础。方法：收集天津医科大学附属肿瘤医院2006年4 月～2007年12月间收治的具有完整临床及病理资料的8 例散发性副神经节瘤患者、1 例家族性副神经节瘤患者及其4 位亲属的外周血标本。留取 18例正常人外周血标本作为对照。扩增 SDHD、SDHB 基因各外显子,纯化后直接进行DNA序列测定,将测序结果与美国生物技术信息中心公布的标准序列比对。结果：家族性PGL 病例检测到SDHD 基因杂合性错义突变,8 例散发性副神经节瘤病例未检测到SDHD 基因外显子突变。2 例散发性PGL 病例携带SDHB 基因第一外显子同义突变,发病时间早于不伴该同义突变者,且病理上均为恶性。家族性病例未检测到SDHB 基因突变。结论：家族性PGL 病例携带SDHD 基因突变,而散发性PGL 病例中未发现SDHD 基因突变,提示SDHD 基因突变可能是国人家族性副神经节瘤发病的分子基础之一。散发性副神经节瘤病例检测到SDHB 基因第一外显子同义突变A6A,有该突变的患者病理上均为恶性,提示A6A 可能影响副神经节瘤的表型。     

Active succinate dehydrogenase (SDH) and lack of SDHD mutations in sporadic paragangliomas

BACKGROUND: Paragangliomas are benign, slow-growing tumours of the head and neck region. The candidate gene for familial and some sporadic paragangliomas, SDHD (succinate dehydrogenase, subunit D), has been mapped to the PGL1 locus in 11q23.3. MATERIALS AND METHODS: Normal and tumour DNA of 17 patients with sporadic paragangliomas were analysed by sequencing (SDHD, SDHB and SDHC genes), fluorescence in situ hybridisation (FISH). In addition, loss of heterozygosity (LOH) and succinate dehydrogenase (SDH) enzyme activity assays were performed. RESULTS AND CONCLUSION: Only two patients from our collective showed SDH gene mutations, one in SDHD and one in SDHB, respectively. Moreover, SDH activity detected in 5/8 patients confirmed the fact that SDH inactivation is not a major event in sporadic paragangliomas. LOH and FISH analysis demonstrated a frequent loss of regions within chromosome 11, indicating that additional genes in 11q may play a role in tumour genesis of sporadic paragangliomas.     

Somatic loss of maternal chromosome 11 causes parent-of-origin-dependent inheritance in SDHD-linked paraganglioma and phaeochromocytoma families

Germline mutations in succinate dehydrogenase subunits B, C and D (SDHB, SDHC and SDHD), genes encoding subunits of mitochondrial complex II, cause hereditary paragangliomas and phaeochromocytomas. In SDHB (1p36)- and SDHC (1q21)-linked families, disease inheritance is autosomal dominant. In SDHD (11q23)-linked families, the disease phenotype is expressed only upon paternal transmission of the mutation, consistent with maternal imprinting. However, SDHD shows biallelic expression in brain, kidney and lymphoid tissues (Baysal et al., 2000). Moreover, consistent loss of the wild-type (wt) maternal allele in SDHD-linked tumours suggests expression of the maternal SDHD allele in normal paraganglia. Here we demonstrate exclusive loss of the entire maternal chromosome 11 in SDHD-linked paragangliomas and phaeochromocytomas, suggesting that combined loss of the wt SDHD allele and maternal 11p region is essential for tumorigenesis. We hypothesize that this is driven by selective loss of one or more imprinted genes in the 11p15 region. In paternally, but not in maternally derived SDHD mutation carriers, this can be achieved by a single event, that is, non-disjunctional loss of the maternal chromosome 11. Thus, the exclusive paternal transmission of the disease can be explained by a somatic genetic mechanism targeting both the SDHD gene on 11q23 and a paternally imprinted gene on 11p15.5, rather than imprinting of SDHD.     

Prognostic value of RET proto-oncogene point mutations in malignant and benign,sporadic phaeochromocytomas

Somatic mutations in the RET proto-oncogene are involved in the pathogenesis of an important subset (40–60%) of sporadic medullary thyroid carcinomas (MTCs) and less frequently (0–31%) in benign, sporadic phaeochromocytomas. Since limited data exist regarding the significance of somatic RET mutations in malignant phaeochromocytomas, we analysed a multicentre series of proven malignant (i.e., metastasised) phaeochromocytomas. Analogous with MTCs, where RET mutations lead to an aggressive behaviour, we hypothesised that somatic mutations would occur more frequently in malignant than in benign phaeochromocytomas. Paraffin-embedded tissue was available from 29 malignant and 27 benign phaeochromocytomas. Exons 10, 11 and 16 were analysed by non-radioactive single-strand conformation polymorphism, heteroduplex gel electrophoresis, restriction enzyme digestion and aberrant band patterns by non-isotopic sequencing. In only 1 of 29 malignant phaeochromocytomas was a mis-sense mutation found (at codon 634 of exon 11), whereas in 15% (4/27) of the benign tumours a point mutation was detected (in 3 tumours in exon 16 at codon 918 and in 1 tumour in exon 10 at codon 618). Absence of these mutations in non-tumourous DNA proved their somatic origin. Contrary to what has been reported for MTCs, oncogenic RET mutations are not associated with an aggressive tumour behaviour in sporadic phaeochromocytomas. Int. J. Cancer (Pred. Oncol.) 79:537–540, 1998.© 1998 Wiley-Liss, Inc.     

Clinical and biochemical features of sporadic and hereditary phaeochromocytomas: an analysis of 41 cases investigated in a single endocrine centre.

The aims of this study were to estimate the prevalence of phaeochromocytomas among adrenal tumours and to analyse the clinical and biochemical features of sporadic and hereditary tumours. Our series of 609 adrenal tumours evaluated between January 1995 and July 2003 was reviewed. Catecholamine content in phaeochromocytoma tissues was also determined and correlated with clinical behaviour and biochemical parameters of patients. Forty-one (6.7%) of the 609 patients had phaeochromocytomas, of which 28 were sporadic (25 benign and three malignant) and 13 (all benign) were associated with hereditary diseases (multiple endocrine neoplasia type 2A in seven cases from four unrelated families carrying mutations of the RET gene, von Hippel-Lindau disease in two unrelated cases with mutations of the VHL gene, and type 1 neurofibromatosis in four unrelated cases). Bilateral tumours were found in three patients with hereditary syndromes and in one sporadic case. Tumour diameter was slightly but not significantly greater in patients with hereditary than in those with sporadic tumours. Systolic but not diastolic blood pressure was significantly higher in patients with sporadic compared with those with hereditary tumours, but comparison of other clinical data and biochemical parameters indicated an absence of significant differences in the mean age, presenting symptoms, heart rate, or fasting serum glucose levels. Tissue catecholamine content measured in 8 sporadic and 5 hereditary phaeochromocytomas was highly variable and it failed to show significant differences between hereditary and sporadic tumours. These results indicate a high proportion of hereditary diseases among patients with phaeochromocytomas. Genetic and clinical testing for hereditary diseases may be of great help to offer an appropriate treatment, follow-up and family screening for these patients.     

Somatic and occult germ-line mutations in SDHD, a mitochondrial complex II gene, in nonfamilial pheochromocytoma

Most pheochromocytomas are sporadic but about 10% are though to be hereditary. Although the etiology of most inherited pheochromocytoma is well known, little is known about the etiology of the more common sporadic tumor. Recently, germ-line mutations of SDHD, a mitochondria complex II gene, were found in patients with hereditary paraganglioma. We sought to determine whether SDHD plays a role in the development of sporadic pheochromocytomas and performed a mutation and deletion analysis of SDHD. Among 18 samples, we identified 4 heterozygous sequence variants (3 germ-line, 1 somatic). One germ-line SDHD mutation IVS1+2T>G (absent among 78 control alleles) is predicted to cause aberrant splicing. On reinvestigation, this patient was found to have a tumor of the carotid body, which was likely a paraganglioma. Another patient with malignant, extra-adrenal pheochromocytoma was found to have germ-line c.34G> A (G12S). However, this sequence variant was also found in 1 of 78 control alleles. The third, germ-line nonsense mutation R38X was found in a patient with extra-adrenal pheochromocytoma. The only somatic heterozygous mutation, c.242C>T (P81L), has been found in the germ line of two families with hereditary paraganglioma and is conserved among four eukaryotic multicellular organisms. Hence, this mutation is most likely of functional significance too. Overall, loss of heterozygosity in at least one of the two markers flanking SDHD was found in 13 tumors (72%). All of the tumors that already harbored intragenic SDHD mutations, whether germ-line or somatic, also had loss of heterozygosity. Our results indicate that SDHD plays a role in the pathogenesis of pheochromocytoma. Given the minimum estimated germline SDHD mutation frequency of 11% (maximum estimate up to 17%) in this set of apparently sporadic pheochromocytoma cases and if these data can be replicated in other populations, our observations might suggest that all such patients be considered for SDHD mutation analysis.     

Genetic testing in pheochromocytoma or functional paraganglioma.

PURPOSE: To assess the yield and the clinical value of systematic screening of susceptibility genes for patients with pheochromocytoma (pheo) or functional paraganglioma (pgl). PATIENTS AND METHODS: We studied 314 patients with a pheo or a functional pgl, including 56 patients having a family history and/or a syndromic presentation and 258 patients having an apparently sporadic presentation. Clinical data and blood samples were collected, and all five major pheo-pgl susceptibility genes (RET, VHL, SDHB, SDHD, and SDHC) were screened. Neurofibromatosis type 1 was diagnosed from phenotypic criteria. RESULTS: We have identified 86 patients (27.4%) with a hereditary tumor. Among the 56 patients with a family/syndromic presentation, 13 have had neurofibromatosis type 1, and germline mutations on the VHL, RET, SDHD, and SDHB genes were present in 16, 15, nine, and three patients, respectively. Among the 258 patients with an apparently sporadic presentation, 30 (11.6%) had a germline mutation (18 patients on SDHB, nine patients on VHL, two patients on SDHD, and one patient on RET). Mutation carriers were younger and more frequently had bilateral or extra-adrenal tumors. In patients with an SDHB mutation, the tumors were larger, more frequently extra-adrenal, and malignant. CONCLUSION: Genetic testing oriented by family/sporadic presentation should be proposed to all patients with pheo or functional pgl. We suggest an algorithm that would allow the confirmation of suspected inherited disease as well as the diagnosis of unexpected inherited disease.     

Somatic mutation analysis of the SDHB, SDHC, SDHD, and RET genes in the clinical assessment of sporadic and hereditary pheochromocytoma

Systemic analysis of somatic mutations of other susceptibility genes in syndromic tumors as well as apparently sporadic tumors in well-characterized specimens is lacking. Its clinical relevance has not been studied. Our objective was to determine the frequency of second allele inactivation in syndromic tumors and determine the frequency and potential clinical impact of somatic mutations and loss of heterozygosity (LOH) of the known susceptibility genes in syndromic and sporadic tumors. Nine tumor specimens from clinically characterized VHL mutation, five from SDHB mutation, four from SDHD mutation, two from RET mutation carriers, and eight from apparently sporadic cases were analyzed. Tumor DNA mutation screening of the SDHx, VHL, and RET genes and LOH analyses of the SDHx and VHL genes were performed. The Yates-corrected chi-squared test was used for comparison of the clinical data and the molecular-genetic results. Second allele inactivation in tumors was identified in 83% of VHL, 80% of SDHB, and 50% of SDHD specimen. High prevalence of VHL (6/6, p=0.024) and SDHB (7/7, p=0.018) somatic mutations has been identified in the sporadic group compared to all others. In the group of the VHL tumors the SDHB somatic events were significantly lower (2/6; p=0.045). In 18/19 (95%) of cases, we were able to demonstrate the presence of at least two concomitant affected susceptibility genes. We conclude that LOH is the most prevalent second allele-inactivating event. SDHB and VHL somatic mutation might play a role in the sporadic forms of tumor development. There is no clinical impact of mutation screening or LOH analysis of tumor specimens.     

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.     

Pheochromocytoma: the expanding genetic differential diagnosis

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

Frequent germ-line succinate dehydrogenase subunit D gene mutations in patients with apparently sporadic parasympathetic paraganglioma.

PURPOSE: Recently, familial paraganglioma (PGL) was shown to be caused bymutations in the gene encoding succinate dehydrogenase subunit D (SDHD). However, the prevalence of SDHD mutations in apparently sporadic PGL is unknown. We studied the frequency and spectrum of germ-line and somatic SDHD mutations in patients with parasympathetic PGL. EXPERIMENTAL DESIGH: We studied 57 unselected patients who developed parasympathetic PGLs (n = 105 tumors) and who were treated between 1987 and 1999 at the Erasmus MC (Rotterdam, the Netherlands). Thirty-eight (67%) of these patients (n = 51 tumors) lacked a family history of parasympathetic PGL. We used conformation-dependent gel electrophoresis and sequence determination analysis of germ-line and tumor DNA to identify SDHD mutations. We compared the clinical and molecular characteristics of sporadic and hereditary PGLs. RESULTS: Three different SDHD germ-line mutations were identified in 32 of the 57 (56%) patients. These included 19 of 19 (100%) patients with familial PGL and also 13 of 38 (34%) patients with apparently sporadic PGL. All three mutations were characterized as missense mutations (D92Y, L95P, and L139P) in highly conserved regions of the SDHD gene and were not observed in 200 control alleles. No somatic mutations were found. CONCLUSIONS: Germ-line mutations of the SDHD gene are present in a significant number of patients with apparently sporadic parasympathetic PGL. Somatic SDHD mutations do not play a significant role in the sporadic form of this tumor. Genetic testing for SDHD germ-line mutations should be considered for every patient presenting with this tumor, even if a personal or family history of PGL is absent, to allow appropriate clinical management.     

Pheochromocytoma and paraganglioma: understanding the complexities of the genetic background

Pheochromocytomas and paragangliomas (PCC/PGL) are tumors derived from the adrenal medulla or extra-adrenal ganglia, respectively. They are rare and often benign tumors that are associated with high morbidity and mortality due to mass effect and high circulating catecholamines. Although most PCCs and PGLs are thought to be sporadic, over one third are associated with 10 known susceptibility genes. Mutations in three genes causing well characterized tumor syndromes are associated with an increased risk of developing PCCs and PGLs, including VHL (von Hippel-Lindau disease), NF1 (Neurofibromatosis Type 1), and RET (Multiple Endocrine Neoplasia Type 2). Mutations in any of the succinate dehydrogenase (SDH) complex subunit genes (SDHA, SDHB, SDHC, SDHD) can lead to PCCs and PGLs with variable penetrance, as can mutations in the subunit cofactor, SDHAF2. Recently, two additional genes have been identified, TMEM127 and MAX. Although these tumors are rare in the general population, occurring in two to eight per million people, they are more commonly associated with an inherited mutation than any other cancer type. This review summarizes the known germline and somatic mutations leading to the development of PCC and PGL, as well as biochemical profiling for PCCs/PGLs and screening of mutation carriers.     

Identification of MEN1 gene mutations in families with MEN 1 and related disorders

Following identification of the MEN1 gene, we analysed patients from 12 MEN 1 families, 8 sporadic cases of MEN 1, and 13 patients with MEN 1-like symptoms (e.g. cases of familial isolated hyperparathyroidism (FIHPT), familial acromegaly, or atypical MEN 1 cases) for the presence of germline MEN1 mutations. The entire coding region of the MEN1 gene was sequenced, and mutations were detected in 11 MEN 1 families; one sporadic MEN 1 patient, one case of FIHPT and one MEN 1-like case. Constitutional DNA samples from individuals without MEN1 mutations were digested with several restriction enzymes, Southern blotted and probed with MEN1 cDNA to analyse for the presence of larger deletions of the MEN1 gene unable to be detected by PCR. One MEN 1 patient was found to carry such a deletion. This patient was heterozygous for the D418D polymorphism, however sequence analysis of RT-PCR products showed that only the variant allele was transcribed, thus confirming the result obtained by Southern analysis, which indicated loss of a region containing the initiation codon of one allele.     

A novel germline SDHB mutation in a gastrointestinal stromal tumor patient without bona fide features of the Carney–Stratakis dyad

Gastrointestinal stromal tumors (GISTs) are the most common mesenchyme neoplasms of the gastrointestinal tract. Gain-of-function somatic mutations of the KIT or PDGFRA genes represent the most prevalent molecular alterations in GISTs. In Carney-Stratakis dyad, patients portray germline mutations of the succinate dehydrogenase subunits B (SDHB), C (SDHC) and D (SDHD) and develop multifocal GISTs and multicentric paragangliomas (PGLs). We herein report a novel germline SDHB mutation (c.T282A--Ile44Asn) occurring in a 26 years-old patient diagnosed with a spindle cell intermediate risk GIST that did not present KIT/PDGFRA/BRAF gene mutations. Further analyses revealed loss of the wild-type SDHB allele and complete loss of SDHB expression in the tumor tissue. After genetic screening of other family members, we detected in the patient's mother a SDHB mutation without any clinical/laboratorial evidence of GIST or PGL. Altogether, our findings (germline SDHB mutation with absence of PGL in the index case and of GIST and/or PGL in his mother) raise the possibility that this familiar setting corresponds to an incomplete phenotype of the Carney-Stratakis dyad.