Pheochromocytoma Susceptibility Genes Research Articles

Pheochromocytoma: A Clinicopathologic and Molecular Study of 390 Cases From a Single Center.

Pheochromocytomas are rare neuroendocrine tumors arising from chromaffin cells in the adrenal medulla. They may occur sporadically or in the context of hereditary syndromes. All pheochromocytomas are considered to have malignant potential (defined as risk of metastasis, not local invasion). The use of grading systems with incorporated clinical and histopathologic parameters can help but not definitively predict the metastatic potential of pheochromocytomas. The recent discovery of susceptibility genes provided new insights into the pathogenesis and introduced additional approaches to estimate the metastatic risk of pheochromocytoma. However, the prevalence of these genetic signatures in pheochromocytomas has yet to be fully addressed. Therefore, in the present study, we retrospectively reviewed cases of pheochromocytoma from 1980 to 2018 in the archives of our institution. Three hundred ninety cases were identified, and their clinicopathologic characteristics and genetic statuses were analyzed. About 25% of the cases had metastases, which were more common in older patients (median, 49 y) than in younger ones. Univariate and multivariate analyses revealed that older age, Hispanic ethnicity, metastasis, and large primary tumor size were markedly associated with poor overall survival. In contrast, family history of pheochromocytoma, lack of symptoms, and bilateral adrenal involvement were associated with better survival. About 37% of the pheochromocytomas were associated with inherited syndromes. About 52% of tested patients had pathogenic mutations of pheochromocytoma susceptibility genes. Of these, succinate dehydrogenase B gene mutation had the strongest association with metastasis. These data support that genetic testing should be offered to all patients with pheochromocytoma.

A Clinical Roadmap to Investigate the Genetic Basis of Pediatric Pheochromocytoma: Which Genes Should Physicians Think About?

Pheochromocytoma is very rare at a pediatric age, and when it is present, the probability of a causative genetic mutation is high. Due to high costs of genetic surveys and an increasing number of genes associated with pheochromocytoma, a sequential genetic analysis driven by clinical and biochemical phenotypes is advised. The published literature regarding the genetic landscape of pediatric pheochromocytoma is scarce, which may hinder the establishment of genotype-phenotype correlations and the selection of appropriate genetic testing at this population. In the present review, we focus on the clinical phenotypes of pediatric patients with pheochromocytoma in an attempt to contribute to an optimized genetic testing in this clinical context. We describe epidemiological data on the prevalence of pheochromocytoma susceptibility genes, including new genes that are expanding the genetic etiology of this neuroendocrine tumor in pediatric patients. The clinical phenotypes associated with a higher pretest probability for hereditary pheochromocytoma are presented, focusing on differences between pediatric and adult patients. We also describe new syndromes, as well as rates of malignancy and multifocal disease associated with these syndromes and pheochromocytoma susceptibility genes published more recently. Finally, we discuss new tools for genetic screening of patients with pheochromocytoma, with an emphasis on its applicability in a pediatric population.

Identical germline mutations in the TMEM127 gene in two unrelated Japanese patients with bilateral pheochromocytoma

Recently, TMEM127 was shown to be a new pheochromocytoma susceptibility gene; this is consistent with its function as a tumour suppressor gene (Journal of Clinical Endocrinology and Metabolism, 2009, 94, 2817). Most pheochromocytomas arise from the adrenal medulla, and in approximately half of the cases, the tumours are bilateral (Journal of Clinical Endocrinology and Metabolism, 2009, 94, 2817; Journal of the American Medical Association, 2004, 292, 943; Human Mutation, 2010, 31, 41; Science, 2009, 325, 1139). The aim of the present study was to determine whether TMEM127 mutations are involved in the pathogenesis of pheochromocytomas/paragangliomas in Japanese subjects. For this study, 74 unrelated patients with pheochromocytoma/paraganglioma who tested negative for mutations and deletions in RET, VHL, SDHB and SDHD were recruited through a multi-institutional collaborative effort in Japan. The TMEM127 gene sequence was determined in their germline DNA, and tumour DNA was analysed for the loss of heterozygosity. In addition, their TMEM127 gene sequences were compared with sequences from 114 normal healthy, ethnically matched controls. Among the 74 eligible patients, two unrelated patients (2·7%) with bilateral adrenal pheochromocytoma were found to have an identical germline TMEM127 mutation (c.116_119delTGTC, p.Ile41ArgfsX39) associated with 2q deletion loss of heterozygosity, which was also previously described in a Brazilian case (Journal of the American Medical Association, 2004, 292, 943). We also determined that none of the 114 normal healthy controls had this deletion mutation. This is the first report showing that TMEM127 mutation plays a pathological role in pheochromocytoma in an Asian population. Although our surveillance is limited, the prevalence and the phenotype of this gene mutation appear to be similar to those reported in previous studies.

Expression of Saccharomyces cerevisiae Sdh3p and Sdh4p Paralogs Results in Catalytically Active Succinate Dehydrogenase Isoenzymes

Succinate dehydrogenase (SDH), also known as complex II, is required for respiratory growth; it couples the oxidation of succinate to the reduction of ubiquinone. The enzyme is composed of two domains. A membrane-extrinsic catalytic domain composed of the Sdh1p and Sdh2p subunits harbors the flavin and iron-sulfur cluster cofactors. A membrane-intrinsic domain composed of the Sdh3p and Sdh4p subunits interacts with ubiquinone and may coordinate a b-type heme. In many organisms, including Saccharomyces cerevisiae, possible alternative SDH subunits have been identified in the genome. S. cerevisiae contains one paralog of the Sdh3p subunit, Shh3p (YMR118c), and two paralogs of the Sdh4p subunit, Shh4p (YLR164w) and Tim18p (YOR297c). We cloned and expressed these alternative subunits. Shh3p and Shh4p were able to complement Δsdh3 and Δsdh4 deletion mutants, respectively, and support respiratory growth. Tim18p was unable to do so. Microarray and proteomics data indicate that the paralogs are expressed under respiratory and other more restrictive growth conditions. Strains expressing hybrid SDH enzymes have distinct metabolic profiles that we distinguished by (1)H NMR analysis of metabolites. Surprisingly, the Sdh3p subunit can form SDH isoenzymes with Sdh4p or with Shh4p as well as be a subunit of the TIM22 mitochondrial protein import complex.

A novel TMEM127 mutation in a patient with familial bilateral pheochromocytoma

In this report, we describe a new patient with unexplained familial bilateral pheochromocytoma. Following the recent description of TMEM127 as a new pheochromocytoma susceptibility gene, the aim of this study was to test the hypothesis of a causative TMEM127 gene mutation in this patient. Pheochromocytoma susceptibility genes were analyzed in germline DNA and losses of heterozygosity (LOH) assessed by BAC array comparative genomic hybridization in tumor DNA. SDHB expression and S6 kinase (S6K) phosphorylation were analyzed by immunohistochemistry. Genome-wide expression microarray studies were performed, and vascular density was quantified after CD34 immunohistochemistry. A first germline variant was identified in the SDHB gene (c.158G>A; p.Gly53Glu). However, a positive SDHB immunostaining in the tumor indicated that this SDHB variant was a non-functional polymorphism. A novel TMEM127 germline mutation (c.140C>A, p.Ala47Asp) associated with a 2q11 LOH was found. Transcriptome and immunohistochemical analyses showed that TMEM127-related pheochromocytoma clusterized with NF1-related and RET-related tumors in a large series of pheochromocytomas and paragangliomas, exhibited a reduced TMEM127 mRNA expression and displayed a low vascularization. The phosphorylation of S6K observed in this tumor was suggestive of an activation of the MTOR pathway. Pathological and genomic data demonstrated that a TMEM127 gene mutation not previously described was causative of a new case of familial bilateral pheochromocytoma. This report highlights the importance of supplementary analyses on tumor tissue to provide an accurate pheochromocytoma/paraganglioma genetic testing result to affected patients.

Germline mutations in TMEM127 confer susceptibility to pheochromocytoma.

Pheochromocytomas, catecholamine-secreting tumors of neural crest origin, are frequently hereditary1. However, the molecular basis for the majority of these tumors is unknown2. We identified the transmembrane-encoding TMEM127 gene, on chromosome 2q11, as a novel pheochromocytoma susceptibility gene. In a cohort of 103 samples, truncating germline TMEM127 mutations were detected in one-third of familial and about 3% of sporadic-appearing tumors without a known genetic cause. The wild-type allele was consistently deleted in tumor DNA, suggesting a two-hit mechanism of inactivation. Pheochromocytomas with TMEM127 mutations are transcriptionally related to NF1-mutant tumors and, similarly, show hyperphosphorylation of mTOR targets. Accordingly, in vitro gain- and loss-of-function analyses indicate that TMEM127 is a negative regulator of mTOR. TMEM127 dynamically associates with the endomembrane system and colocalizes with perinuclear (activated) mTOR, suggesting a subcompartmental-specific effect. Our studies unveil TMEM127 as a novel tumor suppressor gene and validate the power of hereditary tumors for elucidating cancer pathogenesis.

Clinical Predictors and Algorithm for the Genetic Diagnosis of Pheochromocytoma Patients

Six pheochromocytoma susceptibility genes causing distinct syndromes have been identified; approximately one of three of all pheochromocytoma patients carry a predisposing germline mutation. When four major genes (VHL, RET, SDHB, SDHD) are analyzed in a clinical laboratory, costs are approximately $3,400 per patient. The aim of the study is to systematically obtain a robust algorithm to identify who should be genetically tested, and to determine the order in which genes should be tested. DNA from 989 apparently nonsyndromic patients were scanned for germline mutations in the genes VHL, RET, SDHB, SDHC, and SDHD. Clinical parameters were analyzed as potential predictors for finding mutations by multiple logistic regression, validated by bootstrapping. Cost reduction was calculated between prioritized gene testing compared with that for all genes. Of 989 apparently nonsyndromic pheochromocytoma cases, 187 (19%) harbored germline mutations. Predictors for presence of mutation are age <45 years, multiple pheochromocytoma, extra-adrenal location, and previous head and neck paraganglioma. If we used the presence of any one predictor as indicative of proceeding with gene testing, then 342 (34.6%) patients would be excluded, and only 8 carriers (4.3%) would be missed. We were also able to statistically model the priority of genes to be tested given certain clinical features. E.g., for patients with prior head and neck paraganglioma, the priority would be SDHD>SDHB>RET>VHL. Using the clinical predictor algorithm to prioritize gene testing and order, a 44.7% cost reduction in diagnostic process can be achieved. Clinical parameters can predict for mutation carriers and help prioritize gene testing to reduce costs in nonsyndromic pheochromocytoma presentations.

Pheochromocytomas: From Genetic Diversity to New Paradigms

Pheochromocytomas and paragangliomas are catecholamine-secreting tumors of neural crest origin caused by germline mutations in at least six distinct genes. This genetic heterogeneity has provided a rich source for both the discovery and functional characterization of new tumor-related genes. However, the genetic repertoire of these tumors is still not fully known, and current evidence points to the existence of additional pheochromocytoma susceptibility genes. Here, the unique contributions of three hereditary models of pheochromocytoma that can advance our knowledge of the disease pathogenesis are presented. The first model, loss of succinate dehydrogenase (SDH) function, illustrates how SDHB, C, or D mutations, components of the energy metabolism pathway, serve as a unique system to explore the pervasive metabolic shift of cancer cells towards glycolysis as a source of energy (also known as the Warburg effect) in contrast to the characteristic oxidative phosphorylation of normal cells. In the second model, mechanisms of tumorigenesis distinct from classical pheochromocytoma susceptibility genes are discussed in the context of a novel putative suppressor of neural crest-derived tumors, the KIF1B beta gene. Finally, NF1 loss is highlighted as a valuable study model to investigate the cell lineage selectivity of the Egln3-mediated developmental apoptotic defect of chromaffin precursor cells. Results from these studies may offer clues to understand the tissue specificity of hereditary pheochromocytoma syndromes. These distinct hereditary disease models illustrate how genetic-driven progress has the potential to narrow current gaps in our knowledge of pheochromocytoma and paraganglioma pathogenesis.

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.

New Advances in the Genetics of Pheochromocytoma and Paraganglioma Syndromes

The discovery of the SDH genes in 2000/2001 dramatically changed the genetics of pheochromocytoma (PHEO) and paraganglioma (PGL). Five years on, it is widely accepted that all patients with PHEO/PGL, whatever their age, should undergo genetic testing, because 25-30% of PHEOs are caused by a germline mutation in one of the five PHEO susceptibility genes. However, genetic testing should be targeted according to family and clinical history. The identification of a causal mutation modifies the management and follow-up of the patient and provides an opportunity for presymptomatic genetic testing for other family members. Moreover, the demonstration that the SDH genes, are tumor suppressor genes and that their inactivation is involved in the hypoxia-angiogenic pathway activating the transcription factor hypoxia-inducible factor (HIF) by inhibiting prolyl hydroxylases (PHDs) may lead to the identification of new therapeutic targets for these rare diseases. We discuss here these recent findings and their clinical consequences for the management of PHEO/PGL families and the future of research in this field.

Pheochromocytoma in von Hippel–Lindau disease and neurofibromatosis type 1

Clinical and genetic understanding of chromaffin tumors has been greatly enhanced in the last few years. Although some pheochromocytoma genes may still be unknown, the role of RET, VHL, SDHB, SDHD and NF1 genes is unequivocal and phenotypes are also being better characterized. The loss of function of VHL and NF1 genes can lead to a variety of tumors including phechromocytoma and their mechanism of action is under intensive investigation. Many different mutations are responsible for VHL gene inactivation but only missense mutations have been described so far in families with pheochromocytoma. Because of its large size extensive mutation analysis of the NF1 gene has seldom been performed, and mutations have only been identified in about 15% of patients. Several point mutations have been found in exon 31. Differences in pheochromocytoma phenotype in VHL or NF1 are not very pronounced, but it may be of some interest to consider the two groups separately. In VHL, pheochromocytoma has an earlier onset than in sporadic forms, it is often multiple, and malignancy is less frequent. The mean age of diagnosis is 28 years, the youngest patient being 5 years old. In NF1 patients pheochromocytoma phenotype is similar to sporadic forms. The mean age of pheochromocytoma onset is 42 years; 84% of patients have solitary adrenal tumors, 9.6% have bilateral adrenal disease and 6.1% have ectopic pheochromocytomas; malignant pheochromocytomas were identified in 11.5% of the cases. The group of pheochromocytoma susceptibility genes includes, along with the tumor suppressor genes VHL and NF1, the proto-oncogene RET and the genes encoding succinate dehydrogenase subunit D and succinate dehydrogenase subunit B. Whether there is a common pathway among these different genes is still a matter of debate.

Screening for genetic causes of hypertension.

Monogenic or single-gene forms of human hypertension result from mutations involving regulatory elements of the renin-angiotensin-aldosterone system (RAAS) or occur in syndromes associated with hereditary pheochromocytoma. RAAS gain-of-function mutations result in sodium retention, suppression of plasma renin activity, and often, but not invariably, hypokalemia. Hereditary RAAS syndromes result from intrinsic renal abnormalities (apparent mineralocorticoid excess and Liddle's syndromes) or from mineralocorticoid excess states (congenital adrenal hyperplasia and glucocorticoid-remediable aldosteronism). In the hereditary pheochromocytoma syndromes many asymptomatic individuals are identified because they are at-risk individuals in kindreds with a pheochromocytoma-predisposing syndrome. On the other hand, up to 25% of subjects with presumed "sporadic" pheochromocytoma have germline mutations in one of four pheochromocytoma susceptibility genes (the RET proto-oncogene, von Hippel-Lindau gene, neurofibromatosis F1 gene, and succinate dehydrogenase subunit D and succinate dehydrogenase subunit B genes). Hereditary pheochromocytomas are typically intra-adrenal and bilateral and patients typically present at younger ages compared with sporadic pheochromocytoma.