Succinate Dehydrogenase Mutations Research Articles

Clinicopathological, immunophenotypic and genetic studies of mediastinal paragangliomas†.

Paragangliomas have unique features in the mediastinum, in part due to their location. Because of their paucity, they have not been thoroughly investigated. We studied the clinical, pathological, immunohistochemical and molecular features of mediastinal paragangliomas. Immunohistochemistry, next-generation sequencing mutation panel and the Oncoscan assay were performed. Twenty-four patients with mediastinal paraganglioma (7 men, 29.2%) had a median age of 45.5 years (19.8-72.2). Twenty-one (87.5%) paragangliomas were completely resected. Six (of 24, 25.0%) tumours were considered metastatic. Mitotic activity occurred in 11 (of 24, 45.8%) paragangliomas. Programmed death-ligand 1 (PD-L1) (n = 23) was expressed in 6 (26%) patients in 10% (n = 2) and 1% (n = 4) of tumour cells, respectively. SDHB expression was lost in 19 (of 22, 86.4%) cases. ATRX expression was lost in 11 (of 23, 47.8%) cases. Next-generation sequencing revealed a single pathogenic mutation in 10 (of 19) specimens including SDHB (n = 4), SDHD (n = 6), SDHC (n = 1), ATRX (n = 1), and ≥2 mutations in 2 cases [SDHC and TERT (n = 1); SDHB, ATRX and TP53 (n = 1)]. Germline mutation analysis revealed the same succinate dehydrogenase mutation (or lack thereof) as identified in the paraganglioma in 11 (of 12) cases. During a median follow-up (n = 21) of 4.8 years (0.8-14.9), 3 patients developed metastases; 4 patients died, at least 1 of disease. Mediastinal paragangliomas can be associated with morbidity and mortality. Many mediastinal paragangliomas have been reported to be associated with syndromes such as multiple endocrine neoplasia, von Hippel-Lindau or succinate dehydrogenase syndrome with mutation profiles dominated by alterations in genes associated with these syndromes.

The Role of 68Ga-DOTA-Octreotate PET/CT in Follow-Up of SDH-Associated Pheochromocytoma and Paraganglioma.

Germline succinate dehydrogenase (SDHx) mutation carriers, especially SDHB, are at increased risk for malignancy and require life-long surveillance. Current guidelines recommend periodic whole-body MRI imaging. We assessed the incremental value of 68Ga-DOTA-octreotate (GaTate) positron emission tomography (PET)/CT compared with conventional imaging in such patients. SDHx mutation carriers who had GaTate PET/CT were retrospectively reviewed. Detection of lesions were compared with MRI or CT on a per-patient and per-lesion basis. Proof of lesions were based on histopathology or clinical/imaging follow-up. Twenty consecutive patients (median age, 46 years; 10 males) were reviewed. Fourteen patients had SDHB, four, SDHD, one SDHC, and one SDHA mutation. Fifteen had prior surgery and/or radiotherapy. Indications for PET/CT were as follows: 7 patients for surveillance for previously treated disease, 9 residual disease, 2 asymptomatic mutation carriers, and 2 for elevated catecholamines. Median time between modalities was 1.5 months.GaTate PET/CT had higher sensitivity and specificity than conventional imaging. On a per-patient basis: PET/CT sensitivity 100%, specificity 100%; MRI/CT 85% and 50%. Per-lesion basis: PET/CT sensitivity 100%, specificity 75%; MRI/CT 80% and 25%. PET/CT correctly identified additional small nodal and osseous lesions. MRI/CT had more false-positive findings. Change of management resulted in 40% (8/20 patients): 3 received localized treatment instead of observation, 1 changed to observation given extra disease detected, 4 with metastases had radionuclide therapy. GaTate PET/CT provided incremental diagnostic information with consequent management impact in SDHx-pheochromocytoma and paraganglioma. Incorporating this modality as part of a surveillance program seems prudent. Further research is needed to define the optimal surveillance strategy including use of MRI.

Higher risk of phaeochromocytoma/paraganglioma (Phaeo-Pgl) in SDHD than SDHB carriers: an Australian cohort study.

Carriers of succinate dehydrogenase (SDHx) mutations are at risk of developing phaeochromocytomas, catecholamine secreting extra-adrenal paragangliomas and non-secretory head and neck paragangliomas and require lifelong surveillance. There is no current consensus on the optimal surveillance strategy. This study describes the outcomes of a cohort of 50 SDHx mutation carriers followed at a tertiary Australian hospital using a surveillance protocol involving annual clinical review with plasma/urine metanephrines and biennial magnetic resonance imaging from skull base to pelvis.

Is routine genetic testing warranted in head and neck paragangliomas?

Is routine genetic testing warranted in head and neck paragangliomas?

Clinical utility of chromogranin A for the surveillance of succinate dehydrogenase B- and succinate dehydrogenase D-related paraganglioma.

Patients with mutations of succinate dehydrogenase B (SDHB) and succinate dehydrogenase D (SDHD) are at high risk of paraganglioma necessitating surveillance. Chromogranin A has been proposed as a biochemical marker of paraganglioma. We sought to determine the diagnostic utility of chromogranin A in a population-based SDHx sample. Tasmania is an island state with one tertiary referral centre for endocrine neoplasia. We performed a cross-sectional analysis of all adult SDHB ( n = 52) and SDHD ( n = 10) patients undergoing paraganglioma surveillance between 2011 and 2017. Chromogranin A was referenced against the outcome of paraganglioma surveillance with a minimum of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) and plasma metanephrines (metanephrine and normetanephrine). Chromogranin A correctly predicted the result of paraganglioma surveillance more often in patients with SDHB compared with those with SDHD (77% vs. 22%, P = 0.003). In the SDHB group, chromogranin A demonstrated a sensitivity of 67% and specificity of 79% compared with 22% and 0% in the SDHD group. Chromogranin A identified one of three PET/CT-visualized SDHB-related paragangliomas with normal plasma metanephrines at the expense of nine false-positive results. A normal chromogranin A demonstrated a negative predictive value of 92% for SDHB-related paraganglioma. In patients with SDHB, plasma normetanephrine and metanephrine offered superior specificity (100%, P = 0.01 and 100%, P < 0.01, respectively) with comparable sensitivity (67%, P = 1.0 and 11%, P = 0.06, respectively) to chromogranin A. Chromogranin A does not provide additive benefit to standard surveillance for predicting the presence of SDHB- or SDHD-related paraganglioma, but has a useful negative predictive value when normal in patients with SDHB mutation.

Primary fibroblast co-culture stimulates growth and metabolism in Sdhb-impaired mouse pheochromocytoma MTT cells.

Pheochromocytomas and paragangliomas (PGLs) due to mutations of succinate dehydrogenase (SDH) B, a subunit of the SDH complex with a role in the Krebs cycle and the respiratory chain, tend to be larger at diagnosis and more prone to metastatic disease than other tumors. This presentation contrasts with the behavior of some cell line models of SDHB impairment, which show reduced growth compared to wild type. We hypothesize that reduced growth of SDHB-impaired monolayer culture models might reflect lack of support from sources within the tumor microenvironment. The present study therefore investigates how the microenvironment, modeled here by fibroblast co-culture, modulates cell metabolism, growth and invasion in an Sdhb-impaired mouse pheochromocytoma cell line. We employed two different constructs of short hairpin RNA to knockdown Sdhb and compared growth in a monolayer with and without fibroblast co-culture. Sdhb-silenced cells showed functional impairment of SDH with elevated succinate to fumarate ratio and decreased oxidative capacity. Cell growth was delayed with an increase in doubling time of 2h or 20h. Clonogenic cell survival and viability, on the other hand, were either unchanged or increased compared to control. In standard monolayer culture, no differences in pro-metastatic features were present. Co-culture with primary mouse fibroblast reversed the difference of proliferation between control and Sdhb knockdown but was unable to significantly influence invasiveness under these culture conditions. Metabolic studies identified that lactate secreted by fibroblasts was taken up preferentially by Sdhb-silenced cells. In summary, the present study identified a potential role for the tumor microenvironment in influencing phenotypic features of SDHB-mutated PGLs, providing a basis for the use of therapies targeted towards the tumor microenvironment.

SDHB mutated paraganglioma imitating thyroid tumor: A case report and review of literature

Paragangliomas of the head and neck are uncommon tumors arising from parasympathetic ganglia. Paragangliomas are mostly asymptomatic and may manifest as palpable mass of neck. The morphologic features are non-specific and comparable to the other neuroendocrine tumors. Most of hereditary cases are associated with alterations in genes of succinate dehydrogenase (SDH). SDHA and SDHB immunohistochemistry is considered as reliable screening method to detect tumors with genetical alterations. Of note, SDHB mutated paragangliomas have the highest risk of local recurrence, distant metastasis and the development of other tumor phenotypes, which are associated with mutation. Therefore, active surveillance of patients and early surgical treatment are essential. In contrast, SDHB mutated head and neck paragangliomas was considered as completely benign tumors, although, the latest literature describes more controversial cases, which may increase awareness. Here, we present a rare case of 21 years old female with asymptomatic neck paraganglioma, which was unexpectedly diagnosed after pathological and immunohistochemical testing of removed thyroid gland and showed unusual immunohistochemical variation for SDH mutation.

Treatment responses to antiangiogenetic therapy and chemotherapy in nonsecreting paraganglioma (PGL4) of urinary bladder with SDHB mutation

Introduction:Paraganglioma (PGL) is a rare neuroendocrine tumor. Currently, the malignancy is defined as the presence of metastatic spread at presentation or during follow-up. Several gene mutations are listed in the pathogenesis of PGL, among which succinate dehydrogenase (SDHX), particularly the SDHB isoform, is the main gene involved in malignancy. A 55-year-old male without evidence of catecholamine secretion had surgery for PGL of the urinary bladder. After 1 year, he showed a relapse of disease and demonstrated malignant PGL without evidence of catecholamine secretion with a germline heterozygous mutation of succinate dehydrogenase B (SDHB). After failure of a second surgery for relapse, he started medical treatment with sunitinib daily but discontinued due to serious side effects. Cyclophosphamide, vincristine, and dacarbazine (CVD) chemotherapeutic regimen stopped the disease progression for 7 months.Conclusion:Malignant PGL is a very rare tumor, and SDHB mutations must be always considered in molecular diagnosis because they represent a critical event in the progression of the oncological disease. Currently, there are few therapeutic protocols, and it is often difficult, as this case demonstrates, to decide on a treatment option according to a reasoned set of choices.

Sdha+/- Rats Display Minimal Muscle Pathology Without Significant Behavioral or Biochemical Abnormalities.

Mitochondrial diseases (MDs) result from alteration of the mitochondrial respiratory chain (MRC) function. Despite the prevalence of MDs in the population, the paucity of animal models available limits the understanding of these disorders. Mutations in SDHA, a gene that codes for the alpha subunit of succinate dehydrogenase (SDH), can cause some forms of MD. SDHA is a crucial contributor to MRC function. In order to expand the range of MD animal models available, we attempted to generate a Sdha knockout rat. Since homozygous Sdha-/- rats could neither be identified in newborn litters, nor as early as embryonic day 14, we evaluated wild-type (WT) and heterozygous Sdha+/- genotypes. No differences in behavioral, biochemical, or molecular evaluations were observed between WT and Sdha+/- rats at 6 weeks or 6 months of age. However, 30% of Sdha+/- rats displayed mild muscle fiber atrophy with rare fibers negative for cytochrome oxidase and SDH on histochemical staining. Collectively, our data provide additional evidence that modeling SDH mutations in rodents may be challenging due to animal viability, and heterozygous rats are insufficiently symptomatic at a phenotypic and molecular level to be of significant use in the study of SDH deficiency.

Abstract CN04-03: Targeting the metabolic basis of kidney cancer

Abstract Renal cell carcinoma (RCC) affects nearly 300,000 people worldwide each year and is responsible for over 100,000 deaths each year. RCC is not a single disease; it is made up of a number of different types of cancer, with different histologies and clinical courses, responding differently to therapy and caused by different genes. There are currently 17 genes known to cause RCC, 14 of which are associated with inherited forms of the disease. Study of the RCC gene pathways has shown that RCC is fundamentally a metabolic disease. Much of what is known about the genetic basis of RCC has been learned from studying RCC-predisposition families. von Hippel-Lindau (VHL) is a hereditary cancer syndrome in which affected individuals are at risk for the development of tumors in a number of organs, including the kidneys. Patients affected with VHL are at risk for the development of bilateral, multifocal, clear cell renal cell carcinoma. Genetic linkage analysis in VHL families was performed to identify the VHL gene on the short arm of chromosome 3. VHL gene mutation that segregates with the disease is identified in 100% of VHL families. VHL gene mutation or methylation is also found in a high percentage of tumors from patients with sporadic, nonfamilial clear cell RCC. The product of the VHL gene, pVHL, has been found to form a complex with elongin C, elongin B, Cul2, and RBX1 to target the hypoxia-induced factors, HIF1/2, for oxygen-dependent ubiquitin-mediated degradation. Although 9 targeted therapeutic agents have been approved by the FDA for the treatment of patients with advanced RCC, many patients eventually progress and may succumb to this disease. High-grade, high-stage, low-survival clear cell RCC has been shown to be characterized by a pattern consistent with aerobic glycolysis, reduced oxidative phosphorylation, and a dependence on the pentose phosphate shunt. Clinical trials targeting the metabolic basis of clear cell RCC, including targeting HIF2 transcription, are currently under way. Hereditary papillary renal cell carcinoma (HPRC) is a hereditary cancer syndrome in which affected individuals are at risk for the development of bilateral, multifocal type 1 papillary RCC. HPRC is characterized by germline mutation of the MET proto-oncogene. MET gene alteration or amplification is found in a high percentage of tumors from patients with nonhereditary, sporadic Type 1 papillary renal cell carcinoma (PRCC). Clinical trials are currently under way targeting the MET pathway in patients with Type 1 PRCC. Birt-Hogg-Dubé is an inherited form of chromophobe RCC (ChRCC) in which affected individuals are at risk for the development of bilateral multifocal chromophobe and hybrid oncocytic RCC. Genetic linkage analysis identified the FLCN as the Birt-Hogg-Dubé gene. The product of the FLCN gene, folliculin, forms a complex with the FLCN binding proteins, FNIP1/2, and the gamma subunit of AMPK. Inactivation of the FLCN has been shown to result in activation of mTORC1/mTORC2. A clinical trial is currently being conducted to evaluate the effect of targeting the mTORC1 pathway in patients with Birt-Hogg-Dubé-associated renal tumors. Hereditary leiomyomatosis and renal cell carcinoma (HLRCC) is a hereditary cancer syndrome in which affected individuals are at risk for the development of cutaneous and uterine leiomyomas and an aggressive form of Type 2 PRCC. HLRCC is characterized by mutation of the gene for the Krebs cycle enzyme, fumarate hydratase (FH). HLRCC-associated type 2 PRCC has been shown to be characterized by a Warburg shift to aerobic glycolysis with decreased oxidative phosphorylation and a glutamine-dependent reductive carboxylation. Clinical trials are currently under way evaluating the effect of agents targeting the FH pathway in patients with HLRCC-associated RCC. SDH-RCC is an inherited from of renal cell carcinoma that occurs in families with germline mutation of succinate dehydrogenase (SDH) B,C, or D genes. Similar to FH-deficient RCC, SDH-RCC is characterized by a metabolic shift to aerobic glycolysis, significantly impaired oxidative phosphorylation (consistent with complex 2 dysfunction), and a glutamine-dependent reductive carboxylation. SDH-RCC renal tumors are malignant and have a propensity to spread when they are small. Understanding the metabolic basis of renal cell carcinoma has the potential to provide the foundation for the development of more effective forms of therapy for patients with these cancers.

Succinate dehydrogenase (SDH)-deficient neoplasia.

The succinate dehydrogenase (SDH) complex is a key respiratory enzyme composed of four subunits: SDHA, SDHB, SDHC and SDHD. Remarkably, immunohistochemistry for SDHB becomes negative whenever there is bi-alleic inactivation of any component of SDH, which is very rare in the absence of syndromic disease. Therefore, loss of SDHB immunohistochemistry serves as a marker of syndromic disease, usually germline mutation of one of the SDH subunits. Tumours which show loss of SDHB expression are termed succinate dehydrogenase-deficient. In addition to loss of SDHB, tumours associated with SDHA mutation also show loss of SDHA expression. Fifteen per cent of pheochromocytoma and paraganglioma (PHEO/PGL) are associated with germline SDH mutation, and therefore SDH-deficient. We recommend screening SDHB immunohistochemistry for all PHEO/PGL. SDH-deficient gastrointestinal stromal tumours (GISTs) show distinctive features, including absent KIT proto-oncogene receptor tyrosine kinase/platelet-derived growth factor receptor A (KIT/PDGFRA) mutations [but positive staining for cKIT and DOG1], virtually exclusive gastric location, lobulated growth, multi-focality, a prognosis not predicted by size and mitotic rate, frequent metastasis to lymph nodes and primary resistance to imatinib therapy. Thirty per cent are associated with SDHA germline mutation and 50% are associated with SDHC epimutation (post-zygotic promoter hypermethylation) - the hallmark of the syndromic but non-hereditary Carney triad (SDH- deficient GIST, SDH-deficient paraganglioma and pulmonary chondroma). SDH-deficient renal carcinoma is newly recognized under the World Health Organization (WHO) 2016 classification and shows vacuolated eosinophilic cytoplasmic and cytoplasmic inclusions. It is particularly associated with SDHB mutation, although SDHC and SDHA mutation occur. SDH-deficient pituitary adenomas are recognized, but appear to be the least common SDH-deficient neoplasm.

Head and Neck Paraganglioma: Medical Assessment, Management, and Literature Update

Head and neck paraganglioma (HNPGL) are rare, highly vascular; typically slow growing and mostly benign neoplasms arising from paraganglia cells. HNPGL cause morbidity via mass effect on adjacent structures (particularly the cranial nerves), invasion of the skull base and, rarely, catecholamine secretion with associated systemic effects. The last decade has seen significant progress in the understanding of HNPGL genetics, with pertinent implications for diagnostic assessment and management of patients and their relatives. The implicated genes code for three of the five subunits of mitochondrial enzyme succinate dehydrogenase (SDH); recent literature reports that approximately one third of all HNPGL are associated with SDH mutations—a prevalence significantly greater than traditionally thought. There are distinct phenotypical syndromes associated with mutations in each individual SDH subunit (SDHD, SDHB, SDHC, and SDHAF2). This article focuses on the clinical features of HNPGL, the implications of HNPGL genetics, and the current evidence relating to optimal identification, investigation, and management options in HNPGL, which are supported by reference to a personal series of 60 cases. HNPGL require a systematic and thorough assessment to appropriately guide management decisions, and a suggested algorithm is presented in this article. Recent developments are particularly pertinent to surgeons of multiple disciplines, including otolaryngology, neurosurgery, vascular, and general surgery.

Superiority of 68Ga-DOTATATE over 18F-FDG and anatomic imaging in the detection of succinate dehydrogenase mutation (SDHx )-related pheochromocytoma and paraganglioma in the pediatric population.

To evaluate and compare diagnostic performance of 68Ga-DOTA(0)-Tyr(3)-octreotate (68Ga-DOTATATE) with 18F-fluoro-2-deoxy-D-glucose (18F-FDG) positron emission tomography-computed tomography (PET/CT) and anatomic imaging using computed tomography and/or magnetic resonance (CT/MR) imaging in detection of SDHx-related pheochromocytomas and paragangliomas (PPGLs) in pediatric patients. Nine pediatric patients (5:4, girls:boys; 14.6 ± 2.0years) with an SDHx-related mutation (SDHB:SDHA:SDHD, n = 7:1:1) were included in this retrospective study. At the time of initial diagnosis, 7/9 patients had metastatic disease. They underwent CT/MR imaging along with PET/CT using 68Ga-DOTATATE (n = 9), 18F-FDG (n = 8), and positron emission tomography-magnetic resonance imaging (PET/MR) using 18F-FDG (n = 1). In this manuscript, 18F-FDG PET/CT refers to both 18F-FDG PET/CT and 18F-FDG PET/MR. The per-lesion, per-region, and per-patient detection rates were compared and calculated for each of the imaging modalities. A composite of all functional and anatomic imaging studies served as the imaging comparator. Eight out of nine patients were positive for PPGLs on the imaging studies that demonstrated 107 lesions in 22 anatomic regions on the imaging comparator. The per-lesion detection rates for 68Ga-DOTATATE PET/CT, 18F-FDG PET/CT, and CT/MR imaging were 93.5% (95%CI, 87.0% to 97.3%); 79.4% (95%CI, 70.5% to 86.6%); and 73.8% (95%CI, 64.5% to 81.9%), respectively. The per-lesion detection rate for 68Ga-DOTATATE PET/CT was significantly higher than that of 18F-FDG PET/CT (p = 0.001) or CT/MR imaging (p < 0.001). In all of the anatomic regions except abdomen, the per-lesion detection rates for 68Ga-DOTATATE PET/CT was found to be equal or superior to 18F-FDG PET/CT, and CT/MR imaging. The per-region detection rate was 100% (95%CI, 84.6% to 100%) for 68Ga-DOTATATE PET/CT and 90.9% (95%CI, 70.8% to 98.9%) for both 18F-FDG PET/CT and CT/MR imaging. The per-patient detection rates for 68Ga-DOTATATE PET/CT, 18FDG PET/CT, and CT/MR imaging were all 100% (95%CI, 63.1% to 100%). Our preliminary study demonstrates the superiority of 68Ga-DOTATATE PET/CT in localization of SDHx-related PPGLs in pediatric population compared to 18F-FDG PET/CT and CT/MR imaging with the exception of abdominal (excluding adrenal and liver) lesions, and suggests that it might be considered as a first-line imaging modality in pediatric patients with SDHx-related PPGLs.

Head and neck paragangliomas: A two-decade institutional experience and algorithm for management.

ObjectivesParagangliomas of the head and neck and cranial base are typically benign, slow‐growing tumors arising within the jugular foramen, middle ear, carotid bifurcation, or vagus nerve proper. The objective of this study was to provide a comprehensive characterization of our institutional experience with clinical management of these tumors and posit an algorithm for diagnostic evaluation and treatment.MethodsThis was a retrospective cohort study of patients undergoing treatment for paragangliomas of the head and neck and cranial base at our institution from 2000–2017. Data on tumor location, catecholamine levels, and specific imaging modalities employed in diagnostic work‐up, pre‐treatment cranial nerve palsy, treatment modality, utilization of preoperative angiographic embolization, complications of treatment, tumor control and recurrence, and hereditary status (ie, succinate dehydrogenase mutations) were collected and summarized.ResultsThe mean (SD) age of our cohort was 51.8 (±16.1) years with 123 (63.4%) female patients and 71 (36.6%) male patients. Catecholamine‐secreting lesions were found in nine (4.6%) patients. Fifty‐one patients underwent genetic testing, with mutations identified in 43 (20 SDHD, 13 SDHB, 7 SDHD, 1 SDHA, SDHAF2, and NF1). Observation with serial imaging, surgical extirpation, radiation, and stereotactic radiosurgery were variably employed as treatment approaches across anatomic subsites.ConclusionAn algorithmic approach to clinical management of these tumors, derived from our longitudinal institutional experience and current empiric evidence, may assist otolaryngologists, radiation oncologists, and geneticists in the care of these complex neoplasms.Level of Evidence4

Biochemical, Molecular, and Clinical Characterization of Succinate Dehydrogenase Subunit A Variants of Unknown Significance.

Purpose: Patients who inherit a pathogenic loss-of-function genetic variant involving one of the four succinate dehydrogenase (SDH) subunit genes have up to an 86% chance of developing one or more cancers by the age of 50. If tumors are identified and removed early in these high-risk patients, they have a higher potential for cure. Unfortunately, many alterations identified in these genes are variants of unknown significance (VUS), confounding the identification of high-risk patients. If we could identify misclassified SDH VUS as benign or pathogenic SDH mutations, we could better select patients for cancer screening procedures and remove tumors at earlier stages.Experimental Design: In this study, we combine data from clinical observations, a functional yeast model, and a computational model to determine the pathogenicity of 22 SDHA VUS. We gathered SDHA VUS from two primary sources: The OHSU Knight Diagnostics Laboratory and the literature. We used a yeast model to identify the functional effect of a VUS on mitochondrial function with a variety of biochemical assays. The computational model was used to visualize variants' effect on protein structure.Results: We were able to draw conclusions on functional effects of variants using our three-prong approach to understanding VUS. We determined that 16 (73%) of the alterations are actually pathogenic, causing loss of SDH function, and six (27%) have no effect upon SDH function.Conclusions: We thus report the reclassification of the majority of the VUS tested as pathogenic, and highlight the need for more thorough functional assessment of inherited SDH variants. Clin Cancer Res; 23(21); 6733-43. ©2017 AACR.

The utility of SDHB and FH immunohistochemistry in patients evaluated for hereditary paraganglioma-pheochromocytoma syndromes

A significant portion of paragangliomas (PGL) and pheochromocytomas (PCC) occur in patients with hereditary PGL/PCC syndromes, including those with germline mutations in succinate dehydrogenase (SDHx) subunit genes. Recently, germline fumarate hydratase (FH) mutations have been identified in a subset of PGL/PCC, and patients with hereditary leiomyomatosis and renal cell carcinoma (HLRCC) may have an increased risk of developing PGL/PCC. SDHB immunohistochemistry (IHC) has previously been shown to be useful for identifying SDHx-deficient PGL/PCC, however, FH IHC has never been explored in these tumors. Thus, we characterized SDHB and FH IHC in a large cohort of PGL/PCC patients (n = 41) at our institution who were evaluated for hereditary PGL/PCC syndromes. Overall, there was strong, positive correlation between germline SDHx subunit gene mutation status and SDHB IHC status (rφ = 0.77; P < .0001), with high corresponding sensitivity, specificity, positive predictive value, and negative predictive value (95.0%, 81.8%, 82.6%, and 94.7%, respectively). Although SDHB loss by IHC was highly correlated with germline SDHx gene mutations, its utility in this population was dependent on clinicopathologic context: while all head and neck PGL patients with SDHB-deficient tumors had germline SDHx gene mutations, only a small subset (25.0%) of PCC patients with SDHB-deficient tumors harbored a germline SDHx gene mutation. Finally, although our cohort contained only one HLRCC patient, their tumor was FH-deficient by IHC, and all other PGL/PCC showed retained FH IHC. Thus, in the appropriate clinical setting, SDHB and FH IHC may be useful for identifying PGL/PCC patients for Medical Genetics evaluation.

The penetrance of paraganglioma and pheochromocytoma in SDHB germline mutation carriers.

Germline mutations in succinate dehydrogenase B (SDHB) predispose to hereditary paraganglioma (PGL) syndrome type 4. The risk of developing PGL or pheochromocytoma (PHEO) in SDHB mutation carriers is subject of recent debate. In the present nationwide cohort study of SDHB mutation carriers identified by the clinical genetics centers of the Netherlands, we have calculated the penetrance of SDHB associated tumors using a novel maximum likelihood estimator. This estimator addresses ascertainment bias and missing data on pedigree size and structure. A total of 195 SDHB mutation carriers were included, carrying 27 different SDHB mutations. The 2 most prevalent SDHB mutations were Dutch founder mutations: a deletion in exon 3 (31% of mutation carriers) and the c.423+1G>A mutation (24% of mutation carriers). One hundred and twelve carriers (57%) displayed no physical, radiological or biochemical evidence of PGL or PHEO. Fifty-four patients had a head and neck PGL (28%), 4 patients had a PHEO (2%), 26 patients an extra-adrenal PGL (13%). The overall penetrance of SDHB mutations is estimated to be 21% at age 50 and 42% at age 70 when adequately corrected for ascertainment. These estimates are lower than previously reported penetrance estimates of SDHB-linked cohorts. Similar disease risks are found for different SDHB germline mutations as well as for male and female SDHB mutation carriers.

Analysis of SDHAF3 in familial and sporadic pheochromocytoma and paraganglioma

BackgroundGermline mutations in genes encoding subunits of succinate dehydrogenase (SDH) are associated with the development of pheochromocytoma (PC) and/or paraganglioma (PGL). As assembly factors have been identified as playing a role in maturation of individual SDH subunits and assembly of the functioning SDH complex, we hypothesized that SDHAF3 variants may be associated with PC/PGL and functionality of SDH.MethodsDNA was extracted from the blood of 37 individuals (from 23 families) with germline SDH mutations and 18 PC/PGL (15 sporadic, 3 familial) and screened for mutations using a custom gene panel, containing SDHAF3 (SDH assembly factor 3) as well as eight known PC/PGL susceptibility genes. Molecular and functional consequences of an identified sequence variant of SDHAF3 were assessed in yeast and mammalian cells (HEK293).ResultsUsing massively parallel sequencing, we identified a variant in SDHAF3, c.157 T > C (p.Phe53Leu), associated with increased prevalence in familial and sporadic PC/PGL (6.6%) when compared to normal populations (1.2% [1000 Genomes], p = 0.003; 2.1% [Exome Aggregation Consortium], p = 0.0063). In silico prediction tools suggest this variant is probably damaging to protein function, hence we assessed molecular and functional consequences of the resulting amino acid change (p.Phe53Leu) in yeast and human cells. We showed that introduction of SDHAF3 p.Phe53Leu into Sdh7 (ortholog of SDHAF3 in humans) null yeast resulted in impaired function, as observed by its failure to restore SDH activity when expressed in Sdh7 null yeast relative to WT SDHAF3. As SDHAF3 is involved in maturation of SDHB, we tested the functional impact of SDHAF3 c.157 T > C and various clinically relevant SDHB mutations on this interaction. Our in vitro studies in human cells show that SDHAF3 interacts with SDHB (residues 46 and 242), with impaired interaction observed in the presence of the SDHAF3 c.157 T > C variant.ConclusionsOur studies reveal novel insights into the biogenesis of SDH, uncovering a vital interaction between SDHAF3 and SDHB. We have shown that SDHAF3 interacts directly with SDHB (residue 242 being key to this interaction), and that a variant in SDHAF3 (c.157 T > C [p.Phe53Leu]) may be more prevalent in individuals with PC/PGL, and is hypomorphic via impaired interaction with SDHB.

Radiological Surveillance Screening in Asymptomatic Succinate Dehydrogenase Mutation Carriers.

There has been a significant increase in the availability of testing for pheochromocytoma and paraganglioma (PPGL) germline susceptibility genes. As more patients with genetic mutations are identified, cascade genetic testing of family members is also increasing. This results in identifying genetic predispositions at a much earlier age. With our current understanding of familial PPGL syndromes, lifelong surveillance is required. This review focuses on carriers of succinate dehydrogenase (SDH) mutations. For genetic testing to be proven worthwhile, the results must be used for patient benefit. For SDHx mutations, this should equate to a surveillance program that is safe and removes as much uncertainty around diagnosis as possible. Early identification of these tumors is the goal of any surveillance program, as surgical resection is the mainstay of treatment with curative intent to prevent the morbidity and mortality consequences associated with catecholamine excess, in addition to the risk of malignancy. Modality and frequency of surveillance imaging and how to engage individuals in the process of surveillance remain controversial questions. The data reviewed here and the cumulative advice supports the avoidance of using radiation-exposing imaging in this group of individuals that require lifelong screening.

A Rare Case of Carney-Stratakis Syndrome in a Patient With SDHA Mutation

Paragangliomas (PGLs) and pheochromocytomas (PCCs) are rare tumors that originate from the neuroendocrine tissue along the paravertebral axis. Up to 35% of these tumors may be hereditary either alone or as a component of a multiple tumor syndrome. The gastrointestinal stromal tumors (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. Most GISTs are driven by gain-of-function mutations in KIT (75-80%) or platelet-derived growth factor receptor-alpha (PDGFRA) (10%). Approximately 15% of GISTs occurring in adults with no KIT or PDGFRA mutations are thermed “wild-type” GISTs. Succinate dehydrogenase (SDH) mutations may contribute to occurrence of wild-type tumors. In 2002, Carney and Stratakis described a new familiar syndrome (CSS) of PGLs/PCCs and GIST caused by germline mutations in SDH. SDH may act as a tumor suppressor gene, and its defects may be oncogenic. In most of CSS cases, the mutations involve the SDHB/C/D subunits; SDHA mutations are reported but extremely rare. We report a case of CSS with a solitary GIST and an incidentally discovered silent PCC harboring an SDHA mutation. J Med Cases. 2017;8(6):191-195 doi: https://doi.org/10.14740/jmc2831w