Genetic predisposition to phaeochromocytoma: analysis of candidate genes GDNF, RET and VHL

Elongin C (ELOC/TCEB1)-associated von Hippel-Lindau disease

Around 95% of patients with clinical features that meet the diagnostic criteria for von Hippel-Lindau disease (VHL) have a detectable inactivating germline variant in VHL. The VHL protein (pVHL) functions as part of the E3 ubiquitin ligase complex comprising pVHL, elongin C, elongin B, cullin 2 and ring box 1 (VCB-CR complex), which plays a key role in oxygen sensing and degradation of hypoxia-inducible factors. To date, only variants in VHL have been shown to cause VHL disease. We undertook trio analysis by whole-exome sequencing in a proband with VHL disease but without a detectable VHL mutation. Molecular studies were also performed on paired DNA extracted from the proband's kidney tumour and blood and bioinformatics analysis of sporadic renal cell carcinoma (RCC) dataset was undertaken. A de novo pathogenic variant in ELOC NM_005648.4(ELOC):c.236A>G (p.Tyr79Cys) gene was identified in the proband. ELOC encodes elongin C, a key component [C] of the VCB-CR complex. The p.Tyr79Cys substitution is a mutational hotspot in sporadic VHL-competent RCC and has previously been shown to mimic the effects of pVHL deficiency on hypoxic signalling. Analysis of an RCC from the proband showed similar findings to that in somatically ELOC-mutated RCC (expression of hypoxia-responsive proteins, no somatic VHL variants and chromosome 8 loss). These findings are consistent with pathogenic ELOC variants being a novel cause for VHL disease and suggest that genetic testing for ELOC variants should be performed in individuals with suspected VHL disease with no detectable VHL variant.

The Role of VHL in the Development of von Hippel-Lindau Disease and Erythrocytosis

Von Hippel-Lindau disease (VHL disease or VHL syndrome) is a familial multisystem neoplastic syndrome stemming from germline disease-associated variants of the VHL tumor suppressor gene on chromosome 3. VHL is involved, through the EPO-VHL-HIF signaling axis, in oxygen sensing and adaptive response to hypoxia, as well as in numerous HIF-independent pathways. The diverse roles of VHL confirm its implication in several crucial cellular processes. VHL variations have been associated with the development of VHL disease and erythrocytosis. The association between genotypes and phenotypes still remains ambiguous for the majority of mutations. It appears that there is a distinction between erythrocytosis-causing VHL variations and VHL variations causing VHL disease with tumor development. Understanding the pathogenic effects of VHL variants might better predict the prognosis and optimize management of the patient.

Molecular markers of paragangliomas/pheochromocytomas

Paragangliomas/pheochromocytomas comprise rare tumors that arise from the extra-adrenal paraganglia, with an incidence of about 2 to 8 per million people each year. Approximately 40% of cases are due to genetic mutations in at least one out of more than 30 causative genes. About 25-30% of pheochromocytomas/paragangliomas develop under the conditions of a hereditary tumor syndrome a third of which are caused by mutations in the VHL gene. Together, the gene mutations in this disorder have implicated multiple processes including signaling pathways, translation initiation, hypoxia regulation, protein synthesis, differentiation, survival, proliferation, and cell growth. The present review contemplates the mutations associated with the development of pheochromocytomas/paragangliomas and their potential to serve as specific markers of these tumors and their progression. These data will improve our understanding of the pathogenesis of these tumors and likely reveal certain features that may be useful for early diagnostics, malignancy prognostics, and the determination of new targets for disease therapeutics.

Haploinsufficiency in tumor predisposition syndromes: altered genomic transcription in morphologically normal cells heterozygous for VHL or TSC mutation

Tumor suppressor genes and their effector pathways have been identified for many dominantly heritable cancers, enabling efforts to intervene early in the course of disease. Our approach on the subject of early intervention was to investigate gene expression patterns of morphologically normal "one-hit" cells before they become hemizygous or homozygous for the inherited mutant gene which is usually required for tumor formation. Here, we studied histologically non-transformed renal epithelial cells from patients with inherited disorders that predispose to renal tumors, including von Hippel-Lindau (VHL) disease and Tuberous Sclerosis (TSC). As controls, we studied histologically normal cells from non-cancerous renal epithelium of patients with sporadic clear cell renal cell carcinoma (ccRCC). Gene expression analyses of VHLmut/wt or TSC1/2mut/wt versus wild-type (WT) cells revealed transcriptomic alterations previously implicated in the transition to precancerous renal lesions. For example, the gene expression changes in VHLmut/wt cells were consistent with activation of the hypoxia response, associated, in part, with the "Warburg effect". Knockdown of any remaining VHL mRNA using shRNA induced secondary expression changes, such as activation of NFκB and interferon pathways, that are fundamentally important in the development of RCC. We posit that this is a general pattern of hereditary cancer predisposition, wherein haploinsufficiency for VHL or TSC1/2, or potentially other tumor susceptibility genes, is sufficient to promote development of early lesions, while cancer results from inactivation of the remaining normal allele. The gene expression changes identified here are related to the metabolic basis of renal cancer and may constitute suitable targets for early intervention.

Von Hippel-Lindau Disease

Von Hippel-Lindau disease is an autosomal dominant syndrome which occurs secondary to germline mutations in the VHL tumor suppressor gene, located on chromosome 3. Clinically von Hippel-Lindau disease is characterized by an increased risk of developing simple visceral cysts, most commonly in the pancreas and kidneys, in addition to an increased risk of developing neoplasms, often with clear cell features, in a multitude of organ systems. The most common neoplasms are cerebellar and retinal hemangioblastomas, adrenal pheochromocytomas, clear cell renal cell carcinomas, pancreatic neuroendocrine tumors, pancreatic serous cystadenomas, and endolymphatic sac tumors. These lesions most commonly present during adulthood; however, screening and surveillance for the development of these lesions should begin in the pediatric years for patients with von Hippel-Lindau disease. In this review article, the genetics and most common neoplasms of von Hippel-Lindau disease are reviewed, with an eye towards implications for the pediatric patient.

Von Hippel-Lindau disease

von Hippel-Lindau (VHL) disease is an inheritable condition with an incidence of 1 in 36000 live births. Individuals with VHL develop benign and malignant tumors including retinal and central nervous system hemangioblastomas, clear cell renal cell carcinomas (RCC), pheochromocytomas, pancreatic neuroendocrine tumors and endolymphatic sac tumors (ELSTs). VHL is caused by germline loss of function of the VHL gene on one allele at chromosome 3p25-26. A somatic "second hit" event leads to the loss of the other allele and tumor formation. Loss of VHL function in cells leads to increased expression and stabilization of hypoxia inducible factor (HIF). VHL protein/HIF pathway has been implicated in tumorigenesis for hemangioblastomas, RCC and other VHL tumors. Clinical examination, imaging, and genetic testing for VHL mutations confirm VHL disease. Management of VHL disease largely consists of surgical resection of symptomatic tumors (hemangioblastomas), tumors prone to metastasize (RCC larger than 3cm), or tumors causing hormonal symptoms (pheochromocytomas). Despite advances in early diagnosis and management of VHL disease, life expectancy for VHL patients remains low at 40-52 years. Secondary effects from VHL manifestations are mitigated by routine surveillance and early detection. In this chapter, we summarize the current state of knowledge in VHL disease.

The genetics of phaeochromocytoma: using clinical features to guide genetic testing

Phaeochromocytoma is a rare, usually benign, tumour predominantly managed by endocrinologists. Over the last decade, major advances have been made in understanding the molecular genetic basis of adrenal and extra-adrenal phaeochromocytoma (also referred to as adrenal phaeochromocytoma (aPCA) and extra-adrenal functional paraganglioma (eFPGL)). In contrast to the previously held belief that only 10% of cases had a genetic component, currently about one-third of all aPCA/eFPGL cases are thought to be attributable to germline mutations in at least nine genes (NF1, RET, SDHA, SDHB, SDHC, SDHD, TMEM127, MAX and VHL). Recognition of inherited cases of aPCA/eFPGL is critical for optimal patient management. Thus, the identification of a germline mutation can predict risks of malignancy, recurrent disease, associated non-chromaffin tumours and risks to other family members. Mutation carriers should be offered specific surveillance programmes (according to the relevant gene). In this review, we will describe the genetics of aPCA/eFPGL and strategies for genetic testing.

Genetics and clinical characteristics of hereditary pheochromocytomas and paragangliomas

Pheochromocytomas (PCCs) and paragangliomas (PGLs) are rare neuroendocrine tumors of the adrenal glands and the sympathetic and parasympathetic paraganglia. They can occur sporadically or as a part of different hereditary tumor syndromes. About 30% of PCCs and PGLs are currently believed to be caused by germline mutations and several novel susceptibility genes have recently been discovered. The clinical presentation, including localization, malignant potential, and age of onset, varies depending on the genetic background of the tumors. By reviewing more than 1700 reported cases of hereditary PCC and PGL, a thorough summary of the genetics and clinical features of these tumors is given, both as part of the classical syndromes such as multiple endocrine neoplasia type 2 (MEN2), von Hippel-Lindau disease, neurofibromatosis type 1, and succinate dehydrogenase-related PCC-PGL and within syndromes associated with a smaller fraction of PCCs/PGLs, such as Carney triad, Carney-Stratakis syndrome, and MEN1. The review also covers the most recently discovered susceptibility genes including KIF1Bβ, EGLN1/PHD2, SDHAF2, TMEM127, SDHA, and MAX, as well as a comparison with the sporadic form. Further, the latest advances in elucidating the cellular pathways involved in PCC and PGL development are discussed in detail. Finally, an algorithm for genetic testing in patients with PCC and PGL is proposed.

Long-term outcomes, branch-specific expressivity, and disease-related mortality in von Hippel-Lindau type 2A

Although a large kindred with familial pheochromocytoma (Pheo) and paraganglioma (PGL) was discovered in 1962 and later found to represent von Hippel-Lindau (VHL) type 2A (mutation Y112H), the phenotype lacks current characterization. Branch-specific expressivity was suspected based on oral family history. Family pedigree analysis, prospective interviews, and extensive record review were used to extend the pedigree, determine phenotype, examine branch-specific expression, and analyze mortality rates over 5 decades. In its 3 known affected branches the kindred now comprises 107 people with or at-risk for VHL, of whom 49 have been diagnosed and 35/49 (71%) are clinically affected. Phenotypic cumulative lifetime risk was 71% for Pheo/PGL, 15% for hemangioblastoma, 33% for retinal angioma, 3% for renal cell carcinoma, and 3% for pancreatic cysts. The mean ages for VHL and Pheo/PGL diagnosis were younger in successive generations. Branch II-4 predominately expressed RA, while branch II-5 predominantly expressed Pheo/PGL. Disease-specific mortality occurred early and was less frequent in successive generations. This analysis of Y112H VHL confirms a high cumulative risk for pheochromocytoma/paraganglioma. Over time, both age at diagnosis and disease-specific mortality have decreased. The observed branch-specific expressivity prompts further study of genetic and environmental disease modifiers in this large family.

von Hippel-Lindau disease: a clinical and scientific review

The autosomal dominantly inherited disorder von Hippel-Lindau disease (VHL) is caused by germline mutations in the VHL tumour suppressor gene (TSG). VHL mutations predispose to the development of a variety of tumours (most commonly retinal and central nervous system haemangioblastomas, clear cell renal carcinoma and phaeochromocytomas). Here, we review the clinical and genetic features of VHL disease, briefly review the molecular pathogenesis and outline clinical management and tumour surveillance strategies.

Mutation analysis of HIF prolyl hydroxylases (PHD/EGLN) in individuals with features of phaeochromocytoma and renal cell carcinoma susceptibility

Germline mutations in the von Hippel-Lindau disease (VHL) and succinate dehydrogenase subunit B (SDHB) genes can cause inherited phaeochromocytoma and/or renal cell carcinoma (RCC). Dysregulation of the hypoxia-inducible factor (HIF) transcription factors has been linked to VHL and SDHB-related RCC; both HIF dysregulation and disordered function of a prolyl hydroxylase domain isoform 3 (PHD3/EGLN3)-related pathway of neuronal apoptosis have been linked to the development of phaeochromocytoma. The 2-oxoglutarate-dependent prolyl hydroxylase enzymes PHD1 (EGLN2), PHD2 (EGLN1) and PHD3 (EGLN3) have a key role in regulating the stability of HIF-α subunits (and hence expression of the HIF-α transcription factors). A germline PHD2 mutation has been reported in association with congenital erythrocytosis and recurrent extra-adrenal phaeochromocytoma. We undertook mutation analysis of PHD1, PHD2 and PHD3 in two cohorts of patients with features of inherited phaeochromocytoma (n=82) and inherited RCC (n=64) and no evidence of germline mutations in known susceptibility genes. No confirmed pathogenic mutations were detected suggesting that mutations in these genes are not a frequent cause of inherited phaeochromocytoma or RCC.

Genotype-phenotype correlations of pheochromocytoma in two large von Hippel-Lindau (VHL) type 2A kindreds with different missense mutations

Von Hippel-Lindau (VHL) disease type 2A is an inherited tumor syndrome characterized by predisposition to pheochromocytoma (pheo), retinal hemangioma (RA), and central nervous system hemangioblastoma (HB). Specific VHL subtypes display genotype-phenotype correlations but, unlike other familial syndromes such as MEN-2, the phenotype in VHL has not yet been stratified at the codon level. Over decades, we have managed two very large VHL type 2A regional kindreds with nearly adjacent but distinct VHL missense mutations. We determined the phenotype of Family 2 and compared the clinical and pathologic parameters of pheo between 30 members of Family 1 (Y112H mutation) and 33 members of Family 2 (Y98H mutation) with mean follow-up of 15.5 and 12.1 years, respectively (P = 0.24). In Family 2, pheo was the most frequent VHL manifestation (79%) and all pheo diagnoses occurred by age 50. Age at first diagnosis was younger in Family 2 than in Family 1 (mean 19.7 vs. 28.8 years; P = 0.02). Pheo expressivity differed by genotype: Family 1 pheo was more likely to be multifocal (P = 0.04), as well as malignant (P < 0.01) and lethal (P = 0.02). Family 1 pheo was also more likely to secrete vanillylmandelic acid (VMA) alone (P = 0.05). This analysis of 130 pheochromocytomas in 63 VHL type 2A patients demonstrates that mutation-specific malignancy and expression patterns exist within the VHL type 2A subtype, and provides information that may help tailor the screening and management algorithms of affected members and those at risk.

Germline VHL gene mutations in Hungarian families with von Hippel-Lindau disease and patients with apparently sporadic unilateral pheochromocytomas

OBJECTIVE

Von Hippel-Lindau (VHL) disease is a hereditary tumor syndrome caused by mutations or deletions of the VHL tumor-suppressor gene. Germline VHL gene alterations may be also present in patients with apparently sporadic pheochromocytoma (ASP), although a wide variation in mutation frequencies has been reported in different patient cohorts.

DESIGN

Herein, we report the analysis of the VHL gene in Hungarian families with VHL disease and in those with ASP.

METHODS

Seven families (35 members) with VHL disease and 37 unrelated patients with unilateral ASP were analyzed. Patients were clinically evaluated and the VHL gene was analyzed using direct sequencing, multiplex ligation-dependent probe amplification, and real-time PCR with SYBR Green chemistry.

RESULTS

Disease-causing genetic abnormalities were identified in each of the seven VHL families and in 3 out of the 37 patients with ASP (one nonsense and six missense mutations, two large gene deletions and one novel 2 bp deletion). Large gene deletions and other genetic alterations resulting in truncated VHL protein were found only in families with VHL type 1, whereas missense mutations were associated mainly, although not exclusively, with VHL type 2B and type 2C.

CONCLUSIONS

The spectrum of VHL gene abnormalities in the Hungarian population is similar to that observed in Western, Japanese, or Chinese VHL kindreds. The presence of VHL gene mutations in 3 out of the 37 patients with ASP suggests that genetic testing is useful not only in patients with VHL disease but also in those with ASP.

Ser80Ile mutation and a concurrent Pro25Leu variant of the VHL gene in an extended Hungarian von Hippel-Lindau family

Von Hippel-Lindau disease (VHL) is a rare autosomal dominant disease characterized by development of cystic and tumorous lesions at multiple sites, including the brain, spinal cord, kidneys, adrenals, pancreas, epididymis and eyes. The clinical phenotype results from molecular abnormalities of the VHL tumor suppressor gene, mapped to human chromosome 3p25-26. The VHL gene encodes two functionally active VHL proteins due to the presence of two translational initiation sites separated by 53 codons. The majority of disease-causing mutations have been detected downstream of the second translational initiation site, but there are conflicting data as to whether few mutations located in the first 53 codons, such as the Pro25Leu could have a pathogenic role. In this paper we report a large Hungarian VHL type 2 family consisting of 32 members in whom a disease-causing AGT80AAT (Ser80Ile) c.239G>A, p.Ser80Ile mutation, but not the concurrent CCT25CTT (Pro25Leu) c.74C>T, p.Pro25Leu variant co-segregated with the disease. To our knowledge, the Ser80Ile mutation has not been previously described in VHL type 2 patients with high risk of pheochromocytoma and renal cell cancer. Therefore, this finding represents a novel genotype-phenotype association and VHL kindreds with Ser80Ile mutation will require careful surveillance for pheochromocytoma. We concluded that the Pro25Leu variant is a rare, neutral variant, but the presence such a rare gene variant may make genetic counseling difficult.

Genetic evaluation of von Hippel-Lindau disease for early diagnosis and improved prognosis

von Hippel-Lindau disease (VHL) is a rare autosomal-dominant disorder in which affected individuals develop tumors in a number of locations. It occurs at a frequency of one per 36,000 population. Metastatic renal cell carcinoma (RCC) remains the leading cause of mortality in patients with clear cell RCC arising from mutations in the VHL tumor suppressor. RCC is the presenting feature in only 10% of VHL patients. VHL patients can present with a number of other renal lesions, such as hemangiomas and benign adenomas, in addition to simple cysts and RCC. We have investigated VHL gene mutations in familial RCC. The study cohort consisted of four patients with synchronous VHL and RCC and 31 kindreds. Analysis of the chromosomes was performed by the Moorehead method. Although none of the kindreds investigated had clinical evidence of VHL disease, 22 were found to have a VHL gene mutation consisting of deletions on the short arm of chromosomes 3, 17, and 19. Detailed clinical examination of the 22 kindreds with a VHL mutation revealed cerebellar hemangioblastoma (three kindreds), meningioma (two) and renal cell carcinoma (five). No VHL gene mutation was detected in nine kindreds. The prevalence of VHL gene mutations was 70.9% in the familial RCC kindreds. As a result of this study, the kindreds of patients with synchronous VHL and RCC have undergone molecular genetic testing and should be investigated for associated disorders.

Pheochromocytoma: advances in genetics, diagnosis, localization, and treatment

Pheochromocytomas are rare, catecholamine-secreting tumors arising most frequently in the chromaffin cells of the adrenal glands. Recent studies have suggested that genetic mutations are more frequent than previously appreciated in patients with these lesions. Advances continue to be made not only in the genetic evaluation of these patients but also in the biochemical confirmation and tumor localization. Surgery remains the definitive treatment, and advances in laparoscopic techniques as well as cortical-sparing procedures have reduced the morbidity associated with tumor resection.

Genotype-phenotype correlations in von Hippel-Lindau disease

von Hippel-Lindau (VHL) disease is a dominantly inherited familial cancer syndrome resulting from mutations in the VHL tumor suppressor gene. VHL disease displays marked variation in expression and the presence of pheochromocytoma has been linked to missense VHL mutations. We analyzed genotype-phenotype correlations in 573 individuals with VHL disease. Routine clinical and radiological surveillance of VHL patients and at-risk relatives was associated with increased detection of retinal angiomatosis (73 vs. 59% of cases) and a reduction in age at diagnosis of renal cell carcinoma (RCC) (44.0+/-10.9 vs. 39.7+/-10.3 years). We confirmed the association of pheochromocytoma with missense mutations described previously, but stratifying missense mutations into those that resulted in substitution of a surface amino acid and those that disrupted structural integrity demonstrated that surface amino acid substitutions conferred a higher pheochromocytoma risk. Age at first manifestation of VHL disease was significantly earlier (P=0.001), and age-related risks of retinal angiomas and RCC were higher (P=0.022 and P=0.0008, respectively) in individuals with a nonsense or frameshift mutation than in those with deletions or missense mutations that disrupted the structural integrity of the VHL gene product (pVHL). These results extend genotype-phenotype-protein structure correlations in VHL disease and provide a baseline for future chemoprevention studies in VHL disease.

VHL mutation analysis in patients with isolated central nervous system haemangioblastoma

Haemangioblastomas of the CNS are a cardinal feature of von Hippel-Lindau (VHL) disease, a dominantly inherited multisystem familial cancer syndrome caused by germline mutation of the VHL tumour suppressor gene. We investigated the frequency of VHL mutations in 188 patients presenting with a single haemangioblastoma, no family history of VHL disease and no evidence of retinal or abdominal manifestations of the disease at the time of diagnosis. We found that approximately 4% of patients had a detectable VHL mutation and all of these cases presented age 40 years or less. Although the identification of a germline VHL mutation has important consequences for the patient (e.g. risk of further CNS and extra-CNS tumours) and their relatives, four patients had germline VHL missense mutations [C162Y, D179N and R200W (two patients)] that may represent haemangioblastoma-only and/or low penetrance mutations. Approximately 5% of patients without a detectable VHL mutation subsequently developed a further 'VHL type tumour' (in most cases a further CNS haemangioblastoma). These findings suggest that a subset of patients with apparently sporadic CNS haemangioblastoma will have a germline VHL mutation but may not be at risk for developing classical VHL disease and a further group may be mosaic for a germline VHL mutation that cannot be detected in blood cells.

Familial nonsyndromic pheochromocytoma

Judging from recent data, heritable forms account for 30-40% of pheochromocytomas. The molecular basis for the familial pheochromocytoma has been largely elucidated and the role of germline mutation of the VHL, RET, SDHB, and SDHD genes has been established. However, on genotyping a group of 172 sporadic or familial pheochromocytomas, we characterized four unrelated probands with familial pheochromocytomas without any sequence variants of RET (exons 8, 10, 11, 13, 14, 15, and 16) or the entire coding sequence of VHL, SDHB, SDHC, SDHD, and EGLN3 (exon-intron boundaries included). The proband of family 1 is a man who had a bilateral pheochromocytoma at the age of 32 and a local recurrence at the age of 48 years. His brother died of malignant pheochromocytoma and his nephew died suddenly of an undiagnosed pheochromocytoma. The proband of family 2 is a female who had a 5-cm benign adrenal pheochromocytoma at the age of 34 years, while her cousin (maternal branch) had a monolateral pheochromocytoma at the age of 42 years. No other tumors had been reported in either family. The proband of family 3 is a female who had a bilateral pheochromocytoma at the age of 66 years. Her sister had a bilateral pheochromocytoma and breast cancer at the age of 54 years. Several other tumors were recorded in this family, including laryngeal cancer, leukemia, and a case of medullary thyroid carcinoma (MTC) in one brother. MTC was naturally ruled out in the proband and her sister. In family 4, the proband was a female who had a bilateral pheochromocytoma at the age of 46 years and a local recurrence a few years later, with liver metastases from the pheochromocytoma. Her brother had a monolateral benign pheochromocytoma. The proband also had a melanoma and bilateral renal cysts. This case revealed a VHL sequence variant IVS2+43 A>G, which was also found in one other unrelated sporadic pheochromocytoma. VHL mRNA integrity is currently being evaluated. The proband had no cerebellar or spinal NMR findings or retinal alterations. In family 5, the proband was a female who had a right adrenal pheochromocytoma at the age of 50 years and a breast cancer at 49 years of age. Her mother had had a right adrenal pheochromocytoma at 61 years of age. Although other molecular mechanisms, such as particular variants in untranslated regions or partial gene deletions, cannot be ruled out, we think finding families with nonsyndromic pheochromocytoma without any RET, VHL, SDHB, SDHC, SDHD, or EGLN3 mutation may argue in favor of the presence of other pheochromocytoma susceptibility genes.

Expression of HIF-1alpha, HIF-2alpha (EPAS1), and their target genes in paraganglioma and pheochromocytoma with VHL and SDH mutations

CONTEXT

Activation of the hypoxia-inducible transcription factors HIF-1 and HIF-2 and a HIF-independent defect in developmental apoptosis have been implicated in the pathogenesis of pheochromocytoma (PCC) associated with VHL, SDHB, and SDHD mutations.

OBJECTIVE

Our objective was to compare protein (HIF-1alpha, EPAS1, SDHB, JunB, CCND1, CD34, CLU) and gene (VEGF, BNIP3) expression patterns in VHL and SDHB/D associated tumors.

RESULTS

Overexpression of HIF-2 was relatively more common in VHL than SDHB/D PCC (12 of 13 vs. 14 of 20, P = 0.02), whereas nuclear HIF-1 staining was relatively more frequent in SDHB/D PCC (19 of 20 vs. 13 of 16, P = 0.04). In addition, CCND1 and VEGF expression (HIF-2 target genes) was significantly higher in VHL than in SDHB/D PCC. These findings suggest that VHL inactivation leads to preferential HIF-2 activation and CCND1 expression as described previously in VHL-defective renal cell carcinoma cell lines but not in other cell types. These similarities between the downstream consequences of VHL inactivation and HIF dysregulation in renal cell carcinoma and PCC may explain how inactivation of the ubiquitously expressed VHL protein results in susceptibility to specific tumor types. Both VHL and SDHB/D PCC demonstrated reduced CLU and SDHB expression. SDHB PCC are associated with a high risk of malignancy, and expression of (proapototic) BNIP3 was significantly lower in SDHB than VHL PCC.

CONCLUSION

Although inactivation of VHL and SDHB/D may disrupt similar HIF-dependent and HIF-independent signaling pathways, their effects on target gene expression are not identical, and this may explain the observed clinical differences in PCC and associated tumors seen with germline VHL and SDHB/D mutations.

Identification of novel VHL targets that are associated with the development of renal cell carcinoma

von Hippel-Lindau (VHL) disease is a dominantly inherited family cancer syndrome characterized by the development of retinal and central nervous system haemangioblastomas, renal cell carcinoma (RCC) and phaeochromocytoma. Specific germline VHL mutations may predispose to haemangioblastomas, RCC and phaeochromocytoma to a varying extent. Although dysregulation of the hypoxia-inducible transcription factor-2 and JunB have been linked to the development of RCC and phaeochromocytoma, respectively, the precise basis for genotype-phenotype correlations in VHL disease have not been defined. To gain insights into the pathogenesis of RCC in VHL disease we compared gene expression microarray profiles in a RCC cell line expressing a Type 1 or Type 2B mutant pVHL (RCC-associated) to those of a Type 2A or 2C mutant (not associated with RCC). We identified 19 differentially expressed novel VHL target genes linked to RCC development. Eight targets were studied in detail by quantitative real-time polymerase chain reaction (three downregulated and five upregulated by wild-type VHL) and for six genes the effect of VHL inactivation was mimicked by hypoxia (but hypoxic-induction of smooth muscle alpha-actin 2 was specific for a RCC cell line). The potential role of four RCC-associated VHL target genes was assessed in vitro. NB thymosin beta (TMSNB) and proteinase-activated receptor 2 (PAR2) (both downregulated by wt pVHL) increased cell growth and motility in a RCC cell line, but aldehyde dehydrogenase (ALDH)1 and ALDH7 had no effect. These findings implicate TMSNB and PAR2 candidate oncogenes in the pathogenesis of VHL-associated RCC.

Laparoscopic Resection of a Paraganglioma of the Organ of Zuckerkandl in a Patient with a Carotid Body Tumor

Paragangliomas of the organ of Zuckerkandl are rare tumors with only several case reports noted in the literature. Synchronous paraganglioma occur sporadically, and on occasion, in association with several genetic syndromes. Paraganglioma of the organ of Zuckerkandl with synchronous carotid body paraganglioma is described herein. Traditionally, surgical resection of abdominal paraganglioma involved an exploratory laparotomy. In this manuscript, we describe one of the first reported laparoscopic resections of this tumor and review the literature on multiple paragangliomas and their associated genetic syndromes.

The von Hippel–Lindau (VHL) germline mutation V84L manifests as early-onset bilateral pheochromocytoma

Von Hippel-Lindau (VHL) disease is a heritable tumor susceptibility syndrome caused by germline mutations in the VHL gene. The types of tumor that can occur in affected individuals include retinal and central nervous system hemangioblastoma, renal cell carcinoma, pheochromocytoma, and others. The pattern of tumor types that develops in a VHL-affected family defines the clinical subtype (1, 2A, 2B, 2C). Generally, it is difficult to accurately predict an individual's clinical phenotype based on their VHL mutation. However, in a few specific VHL mutations, a strong genotype-phenotype correlation has been established. We report here on the clinical findings in individuals from three unrelated families with a V84L VHL germline mutation, and present follow-up information regarding the only other reported family with this missense mutation. In each of these four families, the major clinical manifestation of VHL disease is multiple early-onset pheochromocytomas (VHL type 2C). This series of eight patients strengthens the correlation between the V84L mutation and the VHL type 2C phenotype, and improves our ability to provide prognostic and management recommendations for similarly affected individuals.

Genetic aberrance of sporadic MEN 2A component tumours: analysis of RET

AIM

The molecular pathogenesis of familial multiple endocrine neoplasia (MEN) type 2 (parathyroid adenoma with medullary thyroid carcinoma and adrenal pheochromocytoma) is associated with a germ-line mutation in the RET proto-oncogene. We undertook this study to clarify the relationship between the tumorigenesis of apparently sporadic MEN type 2 component endocrine tumours and RET mutations.

METHODS

Direct sequencing for RET exon 10, 11, 12, 13, 14, 15 and 16 and immunohistochemistry for RET monoclonal antibody were performed on the archival tissues of 84 cases of sporadic endocrine tumours, including 22 medullary thyroid carcinomas (MTCs), 35 adrenal pheochromocytomas (APCs), 18 paragangliomas (PGs), and nine parathyroid adenomas (PTAs).

RESULTS

PCR-based direct sequencing revealed somatic point missense mutation within 22.7% of exon 13 of the RET proto-oncogene (four cases of E768D, one case of S7781) in MTCs. No RET genotype and morphological association was observed in MTCs or APCs. APCs revealed significantly lower levels of immunoexpression of RET, even versus PGs.

CONCLUSIONS

The genetic mutation in RET is relatively low in incidence, and likely to play an insignificant role in the molecular pathogenesis of sporadic MTC. The molecular bases of PG and APC seem to be different despite their embryological and histological similarities.

Hereditary cancer predisposition syndromes

Cancer genetics is increasingly becoming integrated into the practice of modern medical oncology. The ability to distinguish a growing proportion of the 5% to 10% of all cancers that develop in individuals who have inherited a genetic mutation conferring heightened susceptibility to specific cancers may permit targeted efforts in cancer surveillance and prevention. While these individuals comprise a small proportion of the overall burden of cancer, strategies successful in reducing their remarkable cancer risks may be generalizable to the broader population. In this review, we highlight the most common hereditary cancer syndromes, most attributable to genes inherited in an autosomal dominant manner with incomplete penetrance, and a number of rare syndromes in which particular progress has been made. The prevalence, penetrance, tumor spectrum, and underlying genetic defects are discussed and summarized in a large table in which a more comprehensive enumeration of syndromes is provided.

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.

Genetic analysis of mitochondrial complex II subunits SDHD, SDHB and SDHC in paraganglioma and phaeochromocytoma susceptibility

BACKGROUND

Germline mutations in three subunits of mitochondrial complex II (SDHB, SDHC and SDHD) may be associated with susceptibility to phaeochromocytoma (PC) and/or head and neck paraganglioma (HNPGL).

METHODS

To further define the role of SDH subunit mutations in these disorders, we analysed a series of 22 probands with PC and evidence of genetic susceptibility (seven with familial PC only, one with familial PC and HNPGL, 10 sporadic cases with multiple PC and four cases of isolated paediatric onset PC) for germline SDHB, SDHC and SDHD mutations. In addition, we analysed 34 cases of HNPGL (30 isolated cases with single tumours, three isolated cases with multiple tumours and one familial case with multiple tumours) for somatic and germline mutations in SDHB, SDHC and SDHD.

RESULTS

We identified four germline mutations (three SDHB and one SDHD, three novel) in the 22 PC probands. Combining these results with our previous series, we have detected germline SDHB or SDHD mutations in 2/12 (17%) of familial PC only kindreds, 4/5 (80%) of familial PC and HNPGL cases, 1/10 of sporadic multiple PC cases and 2/4 (50%) of paediatric PCs. No somatic mutations were detected in the HNPGL tumours, but four cases with multiple HNPGL had the common P81L germline SDHD mutation. Intriguingly a silent SNP (c.204C > T) in SDHD was significantly more common in HNPGL cases (6/34) than in controls (1/100, P = 0.0011). Combining our results with those from two other large studies in which both SDHB and SDHD have been analysed, SDHB mutations were most commonly associated with phaeochromocytoma susceptibility and SDHD with the development of HNPGL (P = 0.025). However, germline SDHB and SDHD mutations demonstrate considerable phenotypic variability and genotype-phenotype correlations are complex.

CONCLUSION

The significantly lower frequency (P = 0.028) of germline SDH subunit mutations in familial PC only cases compared to those with familial PC and HNPGL suggests that further PC susceptibility gene(s) remain to be identified.

Fine analysis of the short arm of chromosome 1 in sporadic and familial pheochromocytoma

OBJECTIVE

Despite the very recent discovery that about 25% of apparently sporadic forms of pheochromocytoma are actually due to germline mutations of RET, VHL, SDHB or SDHD genes, the genetic bases of the tumourigenesis of this type of cancer are still incompletely understood. Recent studies provided evidence that a new tumour suppressor gene, mapping on the short arm of chromosome 1, could be involved in early tumourigenesis of pheochromocytoma.

DESIGN

We have performed a fine analysis of loss of heterozygosity (LOH) of this region. In particular, we have analysed 31 highly polymorphic microsatellites distributed at 3.8 Mege base (Mb) mean intervals along the short arm of the chromosome 1 in paired samples of DNA extracted from peripheral blood lymphocytes and tumour tissues.

PATIENTS

The study was carried out on 38 patients with pheochromocytoma that had been grouped, by careful clinical and molecular investigation, in the following classes: 21 sporadic, five multiple endocrine neoplasia type 2 (MEN2), two type 1 neurofibromatosis (NF1), five von Hippel-Lindau (VHL), one somatic VHL mutated and four nonsyndromic familial cases.

RESULTS

In 12/21 sporadic cases (57.1%), in 4/5 MEN2 (80%), 2/4 non-syndromic familial cases (50%), and in 2/2 NF1 (100%), the entire short arm was deleted, while in 6/21 sporadic (28.6%) and 1/5 MEN2 (20%) cases a partial deletion was detected. On the other hand, none of the five cases due to VHL mutation (either germline or somatic) had LOH at chromosome 1. In total, complete or partial deletion of 1p was detected in 27/38 (71%) of the cases. The most frequently deleted marker was D1S2890, which maps at 1p32.1. This region, which spans from 50 to 62 Mb from telomere, was therefore further investigated with markers located at a mean interval of 1.3 Mb in the subset of cases that showed a partial deletion of 1p. This analysis showed that a small region between 55.1 and 59.0 Mb was most frequently missing, which could therefore contain a novel pheochromocytoma locus.

CONCLUSIONS

The results presented here confirm that the short arm of chromosome 1 harbours one or more genes responsible for the development of pheochromocytoma and suggest that one of them could map in a 3.9-Mb fragment between 1p32.3 and 1p32.1.

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.

Hereditary paraganglioma targets diverse paraganglia

Paragangliomas are highly vascularised and often heritable tumours derived from paraganglia, a diffuse neuroendocrine system dispersed from skull base to the pelvic floor. The carotid body, a small oxygen sensing organ located at the bifurcation of the carotid artery in the head and neck and the adrenal medulla in the abdomen, are the most common tumour sites. It now appears that mutations in SDHB, SDHC, and SDHD, which encode subunits of mitochondrial complex II (succinate dehydrogenase; succinate-ubiquinone oxidoreductase), are responsible for the majority of familial paragangliomas and also for a significant fraction of non-familial tumours. Germline mutations in complex II genes are associated with the development of paragangliomas in diverse anatomical locations, including phaeochromocytomas, a finding that has important implications for the clinical management of patients and genetic counselling of families. Consequently, patients with a paraganglioma tumour, including phaeochromocytoma, and a complex II germline mutation should be diagnosed with hereditary paraganglioma, regardless of family history, anatomical location, or multiplicity of tumours. This short review attempts to bring together relevant genetic data on paragangliomas with a particular emphasis on head and neck paragangliomas and phaeochromocytomas.

Molecular basis of the VHL hereditary cancer syndrome

The von Hippel-Lindau hereditary cancer syndrome was first described about 100 years ago. The unusual clinical features of this disorder predicted a role for the von Hippel-Lindau gene (VHL) in the oxygen-sensing pathway. Indeed, recent studies of this gene have helped to decipher how cells sense changes in oxygen availability, and have revealed a previously unappreciated role of prolyl hydroxylation in intracellular signalling. These studies, in turn, are laying the foundation for the treatment of a diverse set of disorders, including cancer, myocardial infarction and stroke.

Genetic analysis of RET, GFR alpha 1 and GDNF genes in Spanish families with multiple endocrine neoplasia type 2A

Multiple endocrine neoplasia type 2A (MEN 2A) is associated with specific germline missense mutations in the RET proto-oncogene. This locus encodes a receptor tyrosine kinase whose activation requires the formation of a multimeric receptor complex including GDNF as a ligand and GFR alpha 1 as a coreceptor. In order to explore the role of RET, GFR alpha 1 and GDNF genes in the variation of phenotypes observed in MEN2A families, we analysed germline mutations of these genes in 4 unrelated Spanish MEN2A families (23 cases studied). We found 2 novel variants corresponding to a single change in position + 47 (intron 12) of RET and position +22 (intron 7) of GFR alpha 1. Furthermore, we observed strong co-segregation between 2 polymorphisms of RET [G691S (exon 11) and S904S (TCC-TCG, exon 15) (100%, Fisher's exact test, p< 0.001)]. More interestingly, we found that these polymorphisms occurred at a significantly high frequency in patients with age at onset < 20 years old (Kruskal-Wallis's and Fisher's exact test, p = 0.007). These findings suggest that the G691S and S904S variants of RET may somehow play a role on the age of onset of MEN 2A.

Germ-line mutations in nonsyndromic pheochromocytoma

BACKGROUND

The group of susceptibility genes for pheochromocytoma that included the proto-oncogene RET (associated with multiple endocrine neoplasia type 2 [MEN-2]) and the tumor-suppressor gene VHL (associated with von Hippel-Lindau disease) now also encompasses the newly identified genes for succinate dehydrogenase subunit D (SDHD) and succinate dehydrogenase subunit B (SDHB), which predispose carriers to pheochromocytomas and glomus tumors. We used molecular tools to classify a large cohort of patients with pheochromocytoma with respect to the presence or absence of mutations of one of these four genes and to investigate the relevance of genetic analyses to clinical practice.

METHODS

Peripheral blood from unrelated, consenting registry patients with pheochromocytoma was tested for mutations of RET, VHL, SDHD, and SDHB. Clinical data at first presentation and follow-up were evaluated.

RESULTS

Among 271 patients who presented with nonsyndromic pheochromocytoma and without a family history of the disease, 66 (24 percent) were found to have mutations (mean age, 25 years; 32 men and 34 women). Of these 66, 30 had mutations of VHL, 13 of RET, 11 of SDHD, and 12 of SDHB. Younger age, multifocal tumors, and extraadrenal tumors were significantly associated with the presence of a mutation. However, among the 66 patients who were positive for mutations, only 21 had multifocal pheochromocytoma. Twenty-three (35 percent) presented after the age of 30 years, and 17 (8 percent) after the age of 40. Sixty-one (92 percent) of the patients with mutations were identified solely by molecular testing of VHL, RET, SDHD, and SDHB; these patients had no associated signs and symptoms at presentation.

CONCLUSIONS

Almost one fourth of patients with apparently sporadic pheochromocytoma may be carriers of mutations; routine analysis for mutations of RET, VHL, SDHD, and SDHB is indicated to identify pheochromocytoma-associated syndromes that would otherwise be missed.

Hirschsprung associated GDNF mutations do not prevent RET activation

Hirschsprung disease (HSCR) is a complex disorder characterised by aganglia of distal gastrointestinal tracts. The highest proportion of both familial and sporadic cases is due to mutations of the RET proto-oncogene. Five germline mutations in the glial cell-line-derived neurotrophic factor (GDNF) gene, one of the RET ligands, have been detected in HSCR patients. Pedigrees analysis and the observed association between these GDNF alterations and RET variants in the same patients raised the question of whether the GDNF gene plays any causative/predisposing role in HSCR pathogenesis. In the present work, we have studied the ability of GDNF proteins, each bearing one of the reported mutations, to activate RET by performing a functional test in cultured neuroblastoma cells. Consistently with the lack of genotype/phenotype correlation in human subjects, our results indicate absence of detectable alterations of mutant GDNF induced RET activation.

Recurrent polytopic chromaffin paragangliomas in a 9-year-old boy resulting from a novel germline mutation in the von Hippel-Lindau gene

Pheochromocytomas are frequently associated with inherited cancer syndromes such as von Hippel-Lindau disease (VHL). Retinal angioma and hemangioblastomas of the central nervous system are hallmarks of VHL, but its clinical variety is remarkably broad. Pheochromocytomas as the sole or first manifestation of VHL are rare but have been observed. In this case report, the authors describe an unusual case of initial collapse, seizures, and hypertensive crisis in a child who later was found to have multiple extraadrenal pheochromocytomas. Molecular diagnostics revealed a novel point mutation in the VHL gene (VHL nt. 406 T-->G). Only 7 months after the first lesions had been removed, a new paraganglioma developed in the contralateral periadrenal region. When encountering pheochromocytomas in children, the clinician should be aware that an associated tumor syndrome might be present, and appropriate molecular screening should be initiated. Molecular genetics aid in the clinical decision-making and clinical management of individual patients with pheochromocytoma.

Von Hippel-Lindau disease: clinical and molecular perspectives

Von Hippel-Lindau (VHL) disease (MIM 193300) is the most common cause of familial clear cell renal cell carcinoma (RCC). VHL disease results from germline mutations in the VHL tumor suppressor gene and is characterized by variable expression and the development of benign and malignant neoplasms in multiple organs. The clinical management of VHL disease is challenging and requires a coordinated multidisciplinary approach. However, early detection of VHL tumors by annual surveillance has improved the prognosis for VHL gene carriers. Complex genotype-phenotype correlations for the major manifestations of VHL disease result from allelic heterogeneity and suggest that the VHL gene product has multiple and tissue-specific functions. Recent studies suggest that the VHL protein represents the adaptor unit of an Skp1-Cdc53/Cul1-F-box (SCF)-like protein complex which targets specific proteins for ubiquitinylation and proteolysis. Tumors from VHL patients and sporadic tumors with VHL gene inactivation (e.g., most clear cell RCC) are hypervascular and overexpress hypoxia-inducible mRNAs such as vascular epithelial growth factor (VEGF). Recently, pVHL has been shown to regulate proteolysis of the transcription factors HIF-1 and HIF-2 (EPAS). Thus absence or inactivation of pVHL leads to constitutive HIF-1 and HIF-2 expression, which activates transcription of VEGF and other hypoxia-inducible mRNAs. Evidence for further pVHL functions including roles in fibronectin metabolism and cell cycle regulation has also been reported, but it is unclear whether these functions are mediated via pVHL-targeted proteolysis or other mechanisms. Clinical and laboratory studies of VHL disease have provided a paradigm for demonstrating the importance of familial cancer syndromes in elucidating mechanisms of tumorigenesis in familial and sporadic cancer.

Von Hippel-Lindau disease: gene to bedside

Von Hippel-Lindau is an autosomal dominant familial tumor syndrome with a risk of developing central nervous system and retinal hemangioblastomas, kidney cysts and clear cell carcinoma, cyst adenomas of other organs and pheochromocytoma. Despite continued elaboration of the neurobiologic role of the von Hippel-Lindau protein, the mainstay of management remains the definitive clinical diagnosis of von Hippel-Lindau syndrome (as distinct from sporadic cases of single von Hippel-Lindau-associated tumors), clinical monitoring and preemptive intervention by surgical or ablative therapy. Specific pharmacologic treatment awaits further biologic understanding of critical pathogenic components. Increasingly sensitive imaging and surgical techniques allow for optimum clinical management and intervention. This article will review von Hippel-Lindau molecular genetics, genotype-phenotype correlations and clinical classification, current understanding of the biology of the von Hippel-Lindau protein, its role in the pathophysiology of this disorder and the consequent implications for future therapeutic/interventional strategies. Central nervous system manifestations will be highlighted.

Patogênese molecular do feocromocitoma

Feocromocitoma é um tumor raro originário de células neuroectodérmicas. Em aproximadamente 10% dos casos, estes tumores são herdados. Existem múltiplas formas familiares de feocromocitomas, entre as quais a neoplasia endócrina do tipo 2, a síndrome de von Hippel Lindau, a neurofibromatose tipo 1, formas familiares isoladas de feocromocitoma e possivelmente outros subtipos menos bem caracterizados. Ao mesmo tempo em que se tem observado nos últimos anos um importante avanço quanto à definição do defeito genético responsável pela maior parte das síndromes hereditárias associadas ao feocromocitoma, houve pouco progresso na caracterização da patogênese molecular das variantes esporádicas destes tumores, assim como em grande parte das formas familiares isoladas. Esta revisão apresenta um resumo dos aspectos moleculares das diversas formas de feocromocitomas familiares e esporádicos e finaliza com a proposição de estudos futuros que possam contribuir para elucidar alguns dos muitos aspectos da gênese deste tumor que ainda permanecem obscuros.

Gene mutations in the succinate dehydrogenase subunit SDHB cause susceptibility to familial pheochromocytoma and to familial paraganglioma

The pheochromocytomas are an important cause of secondary hypertension. Although pheochromocytoma susceptibility may be associated with germline mutations in the tumor-suppressor genes VHL and NF1 and in the proto-oncogene RET, the genetic basis for most cases of nonsyndromic familial pheochromocytoma is unknown. Recently, pheochromocytoma susceptibility has been associated with germline SDHD mutations. Germline SDHD mutations were originally described in hereditary paraganglioma, a dominantly inherited disorder characterized by vascular tumors in the head and the neck, most frequently at the carotid bifurcation. The gene products of two components of succinate dehydrogenase, SDHC and SDHD, anchor the gene products of two other components, SDHA and SDHB, which form the catalytic core, to the inner-mitochondrial membrane. Although mutations in SDHC and in SDHD may cause hereditary paraganglioma, germline SDHA mutations are associated with juvenile encephalopathy, and the phenotypic consequences of SDHB mutations have not been defined. To investigate the genetic causes of pheochromocytoma, we analyzed SDHB and SDHC, in familial and in sporadic cases. Inactivating SDHB mutations were detected in two of the five kindreds with familial pheochromocytoma, two of the three kindreds with pheochromocytoma and paraganglioma susceptibility, and 1 of the 24 cases of sporadic pheochromocytoma. These findings extend the link between mitochondrial dysfunction and tumorigenesis and suggest that germline SDHB mutations are an important cause of pheochromocytoma susceptibility.

Genetic testing for cancer predisposition

Clinical cancer genetics is becoming an integral part of the care of cancer patients. This review describes the clinical aspects, genetics, and clinical genetic management of most of the major hereditary cancer susceptibility syndromes. Multiple endocrine neoplasia type 2, von Hippel-Lindau disease, and familial adenomatous polyposis are examples of syndromes for which genetic testing to identify at-risk family members is considered the standard of care. Genetic testing for these syndromes is sensitive and affordable, and it will change medical management. Cancer genetic counseling and testing is probably beneficial in other syndromes, such as the hereditary breast cancer syndromes, hereditary nonpolyposis colorectal cancer syndrome, Peutz-Jeghers syndrome, and juvenile polyposis. There are also hereditary cancer syndromes for which testing is not yet available and/or is unlikely to change medical management, including Li-Fraumeni syndrome and hereditary malignant melanoma. Thorough medical care requires the identification of families likely to have a hereditary cancer susceptibility syndrome for referral to cancer genetics professionals.