SDHD Mutations Research Articles

The clinical phenotype of SDHC-associated hereditary paraganglioma syndrome (PGL3).

Mutations in the genes encoding subunits of the succinate dehydrogenase complex cause hereditary paraganglioma syndromes. Although the phenotypes associated with the more commonly mutated genes, SDHB and SDHD, are well described, less is known about SDHC-associated paragangliomas. To describe functionality, penetrance, number of primary tumors, biological behavior, and location of paragangliomas associated with SDHC mutations. Families with an SDHC mutation were identified through a large cancer genetics registry. A retrospective chart review was conducted with a focus on patient and tumor characteristics. In addition, clinical reports on SDHC-related paragangliomas were identified in the medical literature to further define the phenotype and compare findings. A cancer genetics clinic and registry at a tertiary referral center. Eight index patients with SDHC-related paraganglioma were identified. Three of the eight index patients had mediastinal paraganglioma and four of the eight patients had more than one paraganglioma. Interestingly, the index patients were the only affected individuals in all families. When combining these index cases with reported cases in the medical literature, the mediastinum is the second most common location for SDHC-related paraganglioma (10% of all tumors), occurring in up to 13% of patients. Our findings suggest that thoracic paragangliomas are common in patients with SDHC mutations, and imaging of this area should be included in surveillance of mutation carriers. In addition, the absence of paragangliomas among at-risk relatives of SDHC mutation carriers suggests a less penetrant phenotype as compared to SDHB and SDHD mutations.

Usefulness of Succinate dehydrogenase B (SDHB) immunohistochemistry in guiding mutational screening among patients with pheochromocytoma-paraganglioma syndromes.

Genetic testing of pheochromocytomas (PCC) and paragangliomas (PGL), although expensive, is gradually becoming a part of the routine laboratory investigation for patients with PCC-PGL syndrome. Recently, Succinate dehydrogenase B (SDHB) immunochemistry has been shown to be an excellent indicator of germline mutations in the SDH genes and could help significantly reduce cost. This study assesses the utility of SDHB immunohistochemical analysis when used to guide genetic analysis, with emphasis on cost benefits it could provide in a resource-limited setting. Forty-four cases of PCC/PGL characterized by genetic analysis were included to determine their SDHB expression pattern by immunohistochemistry. SDHB antibody expression was negative among three cases each, with SDHB and SDHD mutations. Immunohistochemistry results were positive for all three cases of RET, a single case of neurofibromatosis and for two cases with Von Hippel-Lindau (VHL) mutations while the remaining two cases with VHL mutations showed a diffuse 'cytoplasmic blush'. Thirty of the remaining 31 samples demonstrated positive staining and were negative for mutations, while a lone sample that was negative for staining and mutation was not included in the final analysis as the internal control for the sample was not adequately stained. Cost analysis in our settings showed that triaging with SDHB immunohistochemistry could potentially reduce costs by USD 320-500 per patient. SDHB immunohistochemistry, when used as a guide to genetic testing, can significantly reduce the effort, time and costs of testing among patients with PCC-PGL, a huge benefit in resource limited settings.

Mutations in SDHD lead to autosomal recessive encephalomyopathy and isolated mitochondrial complex II deficiency

BackgroundDefects of the mitochondrial respiratory chain complex II (succinate dehydrogenase (SDH) complex) are extremely rare. Of the four nuclear encoded proteins composing complex II, only mutations in the 70 kDa...

The enzyme succinate dehydrogenase (SDH) and its role in hereditary pituitary adenomas

Despite active research involving familial pituitary adenomas and characterization of five hereditary syndromes, the genetic defects in more than 80 - 95% of patients remain not found. Besides, there is more than 25 cases of coexistence of pheochromocytomas and pituitary adenomas described in literature that up to date is not integrated in any syndrome; genetic defects of such coexistence also aren't defined. However it is supposed that in pituitary tumorigenesis, germline mutations of SDH can take part that is obviously important aspect of further investigation. Germline mutations of SDH were found in patients with different phenotypes of pituitary adenomas. Studying of mutations in genes SDHD, SDHB, SDHC, SDHA and their prevalence in patients with familial pituitary adenomas or with phenotypes of multiple endocrine neoplasia without mutations in MEN1, CDKN1B, PRKAR1A, AIP genes can provide clarity in a role of mutations in SDH in endocrine and in particular pituitary tumorigenesis.

Role of SDHAF2 and SDHD in von Hippel–Lindau Associated Pheochromocytomas

Pheochromocytomas (PCCs) develop from the adrenal medulla and are often part of a hereditary syndrome such as von Hippel-Lindau (VHL) syndrome. In VHL, only about 30% of patients with a VHL missense mutation develop PCCs. Thus, additional genetic events leading to formation of such tumors in patients with VHL syndrome are sought. SDHAF2 (previously termed SDH5) and SDHD are both located on chromosome 11q and are required for the function of mitochondrial complex II. While SDHAF2 has been shown to be mutated in patients with paragangliomas (PGLs), SDHD mutations have been found both in patients with PCCs and in patients with PGLs. Because loss of 11q is a common event in VHL-associated PCCs, we aimed to investigate whether SDHAF2 and SDHD are targets. In the present study, 41 VHL-associated PCCs were screened for mutations and loss of heterozygosity (LOH) in SDHAF2 or SDHD. Promoter methylation, as well as mRNA expression of SDHAF2 and SDHD, was studied. In addition, immunohistochemistry (IHC) of SDHB, known to be a universal marker for loss of any part the SDH complex, was conducted. LOH was found in more than 50% of the VHL-associated PCCs, and was correlated with a significant decrease (p<0.05) in both SDHAF2 and SDHD mRNA expression, which may be suggestive of a pathogenic role. However, while SDHB protein expression as determined by IHC in a small cohort of tumors was lower in PCCs than in the surrounding adrenal cortex, there was no obvious correlation with LOH or the level of SDHAF2/SDHD mRNA expression. In addition, the lack of mutations and promoter methylation in the investigated samples indicates that other events on chromosome 11 might be involved in the development of PCCs in association with VHL syndrome.

Germline mutations and genotype–phenotype correlations in patients with apparently sporadic pheochromocytoma/paraganglioma in Korea

The aim of our study was to assess the frequency of germline mutations and develop the genetic testing strategy in patients with apparently sporadic pheochromocytoma/paraganglioma (PPGL) in Korea. We included 53 patients diagnosed with non-syndromic PPGL without a family history of PPGLs in three referral centers from 2004 to 2011. Succinate dehydrogenase complex B (SDHB), SDHD, Von Hippel-Lindau (VHL), and rearranged during transfection (RET) genes were examined by direct sequencing and multiple ligation-dependent probe amplification. The study patients were composed of 26 men and 27 women, and mean age was 50.1 ± 13.5 years. The frequency of germline mutations was 13.2% (7/53): RET (n = 2), VHL (n = 1), SDHB (n = 2), and SDHD (n = 2). Six of seven mutation carriers were diagnosed before the age of 50. One of two patients harboring an SDHB mutation had malignant PPGLs. One patient with multifocal head and neck paraganglioma (PGL) and pheochromocytoma (PHEO) carried a SDHD mutation. The carriers of germline mutations in patients with apparently sporadic PPGL were 13.2% in our study. We recommend genetic testing in patients below 50 years and SDHD genetic testing in patients with multifocal PPGLs. In malignant PPGLs, SDHB genetic testing may be performed.

Cowden Syndrome and the PTEN Hamartoma Tumor Syndrome: How to Define Rare Genetic Syndromes

Cowden syndrome (OMIM No. 158350) and Bannayan-Riley-Ruvalcaba syndrome (BRRS) (OMIM No. 153480) are autosomal dominant conditions described before the genetic testing era. The early reports of Cowden syndrome were by adult physicians and dermatologists who recognized a pattern of benign and malignant tumors affecting the breast and thyroid, accompanied by characteristic acral keratosis and trichilemmomas of the skin (1,2,3). BRRS was described by pediatricians and clinical geneticists, with the principle features being macrocephaly, delayed development, lipomata, hemangiomas, and vascular malformations, along with pigmented macules of the penis (4,5). Both conditions are caused by mutations in the PTEN gene (OMIM+601728) (6,7). There is no definite association between the type or position of mutation within the PTEN gene and the clinical presentation of the patient. Both conditions have been described in different members of the same family with the same mutations, and it is clear that meticulous examination reveals features of childhood-onset BRRS in adults presenting with the features of Cowden syndrome and vice versa. It is therefore generally accepted that they are one condition, with variable expression and age-related penetrance (8,9,10,11). Genetic heterogeneity has been reported with reports of Cowden-like patients(ie, those who do not fulfill criteria for PTEN hamartoma syndrome [PHTS]) with mutations in SDHB, SDHD, AKT, and PIK3CA, as well as hypermethylation of the promoter of the KLLN gene (12,13,14,15).

Usefulness of Negative and Weak–Diffuse Pattern of SDHB Immunostaining in Assessment of SDH Mutations in Paragangliomas and Pheochromocytomas

This is a confirmatory study about usefulness of SDHB and SDHA immunostaining in assessment of SDH mutations in paragangliomas and pheochromocytomas. Paraganglioma/pheochromocytoma syndrome (PGL/PCC syndrome) consists of different entities, associated with germline mutations in five different genes: SDHD, SDHAF2, SDHC, SDHA and SDHB. It has been suggested that negative immunostaining of SDHB can be taken as an indicator of the presence of a mutation in one of the five SDH genes. We have performed SDHB and SDHA immunohistochemical staining in a series of paragangliomas and pheochromocytomas from 64 patients. The patients had been previously checked for mutations in SDHD, SDHC and SDHB, but also for mutation in RET and VHL. All 14 patients with SDH mutations (9 with SDHB and 5 with SDHD mutations) exhibited negative or weak-diffuse SDHB staining pattern in tumour tissue, whereas cells of the 23 RET mutated and 8 VHL mutated tumours showed a positive SDHB immunostaining. Sixteen of the patients that did not exhibit a mutation in any gene showed positive SDHB immunostaining in tumour tissue, while only three of the patients without mutation exhibited negative staining. All patients exhibited positive pattern of SDHA immunostaining. The results confirm the value of SDHB immunohistochemical status in assessment of germline mutations in PGL/PCC syndrome.

Illness perceptions, risk perception and worry in SDH mutation carriers

Succinate dehydrogenase (SDH) mutation carriers are predisposed for developing paragangliomas. This study aimed to explore illness perceptions, risk perception and disease-related worry in these individuals. All consecutive SDHB and SDHD mutation carriers followed at the Department of Endocrinology of the Leiden University Medical Center (LUMC), a tertiary referral center, were eligible for inclusion. Illness perceptions were assessed using the validated Illness Perception Questionnaire-Revised and compared to reference populations. Risk perception and worry were measured by two items each and associations with illness perceptions explored. Twenty SDHB and 118 SDHD mutation carriers responded. Compared with various reference groups, SDH mutation carriers perceived less controllability of their condition. SDHB mutation carriers considered their condition to be less chronic in nature (p = 0.005) and perceived more personal (p = 0.018) and treatment control (p = 0.001) than SDHD mutation carriers. Mutation carriers with manifest disease reported more negative illness perceptions and a higher risk perception of developing subsequent tumors than asymptomatic mutation carriers. Illness perceptions, risk perception and disease-related worry were strongly correlated. Risk perception and disease-related worry may be assessed through illness perceptions. The development of interventions targeting illness perceptions may provide tools for genetic counseling.

Paragangliomas: Update on differential diagnostic considerations, composite tumors, and recent genetic developments

Recent developments in molecular genetics have expanded the spectrum of disorders associated with pheochromocytomas (PCCs) and extra-adrenal paragangliomas (PGLs) and have increased the roles of pathologists in helping to guide patient care. At least 30% of these tumors are now known to be hereditary, and germline mutations of at least 10 genes are known to cause the tumors to develop. Genotype-phenotype correlations have been identified, including differences in tumor distribution, catecholamine production, and risk of metastasis, and types of tumors not previously associated with PCC/PGL are now considered in the spectrum of hereditary disease. Important new findings are that mutations of succinate dehydrogenase genes SDHA, SDHB, SDHC, SDHD, and SDHAF2 (collectively "SDHx") are responsible for a large percentage of hereditary PCC/PGL and that SDHB mutations are strongly correlated with extra-adrenal tumor location, metastasis, and poor prognosis. Further, gastrointestinal stromal tumors and renal tumors are now associated with SDHx mutations. A PCC or PGL caused by any of the hereditary susceptibility genes can present as a solitary, apparently sporadic, tumor, and substantial numbers of patients presenting with apparently sporadic tumors harbor occult germline mutations of susceptibility genes. Current roles of pathologists are differential diagnosis of primary tumors and metastases, identification of clues to occult hereditary disease, and triaging of patients for optimal genetic testing by immunohistochemical staining of tumor tissue for the loss of SDHB and SDHA protein. Diagnostic pitfalls are posed by morphological variants of PCC/PGL, unusual anatomic sites of occurrence, and coexisting neuroendocrine tumors of other types in some hereditary syndromes. These pitfalls can be avoided by judicious use of appropriate immunohistochemical stains. Aside from loss of staining for SDHB, criteria for predicting risk of metastasis are still controversial, and "malignancy" is diagnosed only after metastases have occurred. All PCCs/PGLs are considered to pose some risk of metastasis, and long-term follow-up is advised.

No difference in phenotype of the main Dutch SDHD founder mutations

SDHD mutations predispose carriers to hereditary paraganglioma syndrome. The objective of this study was to assess the genotype-phenotype correlation of a large Dutch cohort of SDHD mutation carriers and evaluate potential differences in clinical phenotypes due to specific SDHD gene mutations. Retrospective, descriptive single-centre study. All consecutive SDHD mutation carriers followed at the Department of Endocrinology of the Leiden University Medical Center were included. Subjects were investigated according to structured protocols used for standard care, including repetitive biochemical and radiological screening for paragangliomas. Two hundred and one SDHD mutation carriers with a mean age at presentation of 42·6 ± 14·4 years and a mean follow-up of 5·8 ± 5·4 years were evaluated. Eighty-one percent carried the SDHD c.274G>T (p.Asp92Tyr) mutation and 13% the SDHD c.416T>C (p.Leu139Pro) mutation. No differences in clinical phenotype between these two specific SDHD mutations were found. Ninety-one percent developed one or multiple paragangliomas in the head and neck region (HNPGLs), of which the carotid body tumour was the most prevalent (85%). Eighteen carriers developed pheochromocytomas, fifteen sympathetic paragangliomas and nine carriers (4%) suffered from malignant paraganglioma. By end of follow-up, sixteen SDHD mutation carriers (8%) displayed no biochemical or radiological evidence of manifest disease. The two main Dutch SDHD founder mutations do not differ in clinical expression. SDHD mutations are associated with the development of multiple HNPGLs and predominantly benign disease.

Integrative analysis of miRNA and mRNA expression profiles in pheochromocytoma and paraganglioma identifies genotype-specific markers and potentially regulated pathways

Pheochromocytomas (PCCs) and paragangliomas (PGLs) are rare neuroendocrine neoplasias of neural crest origin that can be part of several inherited syndromes. Although their mRNA profiles are known to depend on genetic background, a number of questions related to tumor biology and clinical behavior remain unanswered. As microRNAs (miRNAs) are key players in the modulation of gene expression, their comprehensive analysis could resolve some of these issues. Through characterization of miRNA profiles in 69 frozen tumors with germline mutations in the genes SDHD, SDHB, VHL, RET, NF1, TMEM127, and MAX, we identified miRNA signatures specific to, as well as common among, the genetic groups of PCCs/PGLs. miRNA expression profiles were validated in an independent series of 30 composed of VHL-, SDHB-, SDHD-, and RET-related formalin-fixed paraffin-embedded PCC/PGL samples using quantitative real-time PCR. Upregulation of miR-210 in VHL- and SDHB-related PCCs/PGLs was verified, while miR-137 and miR-382 were confirmed as generally upregulated in PCCs/PGLs (except in MAX-related tumors). Also, we confirmed overexpression of miR-133b as VHL-specific miRNAs, miR-488 and miR-885-5p as RET-specific miRNAs, and miR-183 and miR-96 as SDHB-specific miRNAs. To determine the potential roles miRNAs play in PCC/PGL pathogenesis, we performed bioinformatic integration and pathway analysis using matched mRNA profiling data that indicated a common enrichment of pathways associated with neuronal and neuroendocrine-like differentiation. We demonstrated that miR-183 and/or miR-96 impede NGF-induced differentiation in PC12 cells. Finally, global proteomic analysis in SDHB and MAX tumors allowed us to determine that miRNA regulation occurs primarily through mRNA degradation in PCCs/PGLs, which partially confirmed our miRNA-mRNA integration results.

Evaluation of SDHB, SDHD and VHL gene susceptibility testing in the assessment of individuals with non‐syndromic phaeochromocytoma, paraganglioma and head and neck paraganglioma

Research studies have reported that about a third of individuals with phaeochromocytoma/paraganglioma (PPGL) have an inherited predisposition, although the frequency of specific mutations can vary between populations. We evaluated VHL, SDHB and SDHD mutation testing in cohorts of patients with non-syndromic PPGL and head and neck paraganglioma (HNPGL). Prospective, observational evaluation of NHS practice. Individuals with PPGL/HNPGL referred to a supraregional genetics testing service over a 10-year period. Clinical (age, tumour site, malignancy, etc.), mutation frequencies and characteristics. A total of 501 probands with PPGL (n = 413) or HNPGL (n = 88) were studied. Thirty-one percent of patients with PPGL presented had a pathogenic mutation in SDHB, SDHD or VHL. Mutation detection rates were highest in those with a positive family history (62%), malignancy (53%), multiple tumours (33%) or PGL (44%). Twenty-eight percent of individuals with a single sporadic phaeochromocytoma had a mutation. Overall, 63% of patients with HNPGL had a mutation (92% of those with a family history, 89% of those with multicentric tumours and 34% of those with a single sporadic HNPGL). Penetrance was calculated in 121 SDHB mutation-positive probands and 187 of their mutation-positive relatives. Most relatives were asymptomatic and lifetime penetrance in non-proband SDHB mutation carriers was <50%. Practice-based evaluations of genetic testing in PPGL reveal high mutation detection rates. Although clinical criteria can be used to prioritize mutation testing, mutations were detected in 'low risk groups' indicating a need for comprehensive and inexpensive genetic testing strategies for PPGL and HNPGL.

SDHA mutations in adult and pediatric wild-type gastrointestinal stromal tumors

Most gastrointestinal stromal tumors (GISTs) harbor oncogenic mutations in KIT or platelet-derived growth factor receptor-α. However, a small subset of GISTs lacks such mutations and is termed ‘wild-type GISTs'. Germline mutation in any of the subunits of succinate dehydrogenase (SDH) predisposes individuals to hereditary paragangliomas and pheochromocytomas. However, germline mutations of the genes encoding SDH subunits A, B, C or D (SDHA, SDHB, SDHC or SDHD; collectively SDHx) are also identified in GISTs. SDHA and SDHB immunohistochemistry are reliable techniques to identify pheochromocytomas and paragangliomas with mutations in SDHA, SDHB, SDHC and SDHD. In this study, we investigated if SDHA immunohistochemistry could also identify SDHA-mutated GISTs. Twenty-four adult wild-type GISTs and nine pediatric/adolescent wild-type GISTs were analyzed with SDHB, and where this was negative, then with SDHA immunohistochemistry. If SDHA immunohistochemistry was negative, sequencing analysis of the entire SDHA coding sequence was performed. All nine pediatric/adolescent GISTs and seven adult wild-type GISTs were negative for SDHB immunohistochemistry. One pediatric GIST and three SDHB-immunonegative adult wild-type GISTs were negative for SDHA immunohistochemistry. In all four SDHA-negative GISTs, a germline SDHA c.91C>T transition was found leading to a nonsense p.Arg31X mutation. Our results demonstrate that SDHA immunohistochemistry on GISTs can identify the presence of an SDHA germline mutation. Identifying GISTs with deficient SDH activity warrants additional genetic testing, evaluation and follow-up for inherited disorders and paragangliomas.

Paraganglioma of the Carotid Body: Treatment Strategy and SDH-gene Mutations

The aim of the present study was to review treatment results in patients with paraganglioma (PGL) of the neck presenting as carotid body tumour, long-term follow-up and relevance of genetic testing for succinate dehydrogenase (SDH)-gene mutations. Retrospective analysis of prospectively collected data and prospective genetic analysis. Over a 25-year period (1987-2011) 50 patients were operated for 63 PGLs of the neck. Pre-, intra- and postoperative findings were analysed. Sanger sequencing was performed for genetic testing of SDH-gene mutations (SDH B, SDHC and SDHD). Fifty patients underwent resection of 63 PGLs (62 benign, one malignant) without mortality. Eight patients underwent preoperative embolisation. Vascular surgical procedures were required in 15 operations (15/63 = 23.8%). Nerve lesions occurred after 13 operations (13/63 = 20.6%) and were associated with large tumours. A total of 44 patients are alive after a mean follow-up of 9.8 years. In 40 patients 17 SDH-gene mutations were detected (17/40 = 42.5%): 14 SDHD mutations, two SDHB mutations and one rare SDHC mutation. Surgery for PGL is recommended. All PGL patients should be screened for SDH mutations because it impacts the individual follow-up strategy. Whereas all PGL patients require annual ultrasound control, mutation carriers and family members with proven mutations should in addition be regularly examined by magnetic resonance imaging (MRI) of head, neck, thorax, abdomen and pelvis.

Quality of life is decreased in patients with paragangliomas

Germline mutations in succinate dehydrogenase (SDH) genes predispose carriers for developing paragangliomas, and studies on their quality of life (QoL) are scarce. The objectives of this study were to assess QoL in patients with paragangliomas (PGL), to evaluate long-term QoL, and to explore potential differences in QoL between SDH mutation carriers and paraganglioma patients without an SDH mutation. Cross-sectional, case-control study. Tertiary referral center. ONE HUNDRED AND SEVENTY FOUR PARAGANGLIOMA PATIENTS WERE INCLUDED: 25 SDHB, two SDHC, and 122 SDHD mutation carriers and 25 patients without an SDH mutation. They provided 100 peers as control persons. Furthermore, patients were compared with age-adjusted reference populations. QOL WAS ASSESSED USING THREE VALIDATED HEALTH-RELATED QOL QUESTIONNAIRES: the Hospital Anxiety and Depression Scale, the Multidimensional Fatigue Index 20, and the Short Form 36. Patients reported a significantly impaired QoL compared with their own controls, mainly on fatigue and physical condition subscales. Compared with age-adjusted literature values, patients had significantly impaired scores on physical, psychological, and social subscales. A decreased QoL was mainly related to paraganglioma-associated complaints. There was no difference in QoL between the various SDH mutation carriers or paraganglioma patients without an SDH mutation. QoL in asymptomatic mutation carriers, i.e. without manifest disease, did not differ from QoL of the general population. Long-term results in 41 patients showed no alteration in QoL besides a reduced level of activity. QoL is decreased in paraganglioma patients but stable when measured over time.

High incidence of extraadrenal paraganglioma in families with SDHx syndromes detected by functional imaging with [18F]fluorodihydroxyphenylalanine PET

Knowledge of the genetic backgrounds of hereditary syndromes, which are increasingly being characterized, enables genetic screening of family members of affected patients. Upon detection of a mutation, genetic counselling and clinical screening including imaging modalities and biochemical analyses are commonly performed. Unaffected, mutation-positive relatives of index patients with hereditary paraganglioma syndromes were offered PET imaging with [(18)F]fluorodihydroxyphenylalanine and the incidence of pathological findings was retrospectively analysed in relation to mutations of the succinate dehydrogenase enzyme complex. PET only or PET/CT was performed in 21 individuals from eight families with SDHD, one family with SDHC and two families with SDHB mutations. Screening was offered every 2 to 5 years. Of the 21 individuals, 14 showed paraganglioma during screening. In particular, in only 2 of 15 patients with a SDHD mutation were the findings completely unremarkable on PET screening. However, false-negative lesions for abdominal manifestations in two SDHD-positive patients were detected. FDOPA PET is a sensitive imaging modality which should be offered to patients with a detected SDHx (SDHD) mutation, preferably using a hybrid technique.

Immunohistochemical Loss of Succinate Dehydrogenase Subunit A (SDHA) in Gastrointestinal Stromal Tumors (GISTs) Signals SDHA Germline Mutation

A subset (7% to 10%) of gastric gastrointestinal stromal tumors (GISTs) is notable for the immunohistochemical loss of succinate dehydrogenase (SDH) subunit B (SDHB), which signals the loss of function of the SDH complex consisting of mitochondrial inner membrane proteins. These SDH-deficient GISTs are known to be KIT/PDGFRA wild type, and most patients affected by this subset of GISTs are young. Some of these patients have germline mutations of SDH subunit genes SDHB, SDHC, or SDHD, known as Carney-Stratakis syndrome when combined with paraganglioma. More recently, germline mutations in SDH subunit A gene (SDHA) have also been reported in few patients with KIT/PDGFRA wild-type GISTs. In this study we immunohistochemically examined 127 SDHB-negative and 556 SDHB-positive gastric GISTs and 261 SDHB-positive intestinal GISTs for SDHA expression using a mouse monoclonal antibody 2E3 (Abcam). Cases with available DNA were tested for SDHA, SDHB, SDHC, and SDHD gene mutations using a hybridization-based custom capture next-generation sequencing assay. A total of 36 SDHA-negative GISTs (28%) were found among 127 SDHB-negative gastric GISTs. No SDHB-positive GIST was SDHA negative. Among 7 SDHA-negative tumors analyzed, there were 7 SDHA mutants, most germline. A second hit indicating biallelic inactivation of SDHA was present in 6 of those cases. These patients had no other SDH subunit gene mutations. Among the 25 SDHA-positive, SDHB-negative GISTs analyzed, we identified 3 SDHA mutations (1 germline), and 11 SDHB, SDHC, or SDHD mutations (mostly germline), and 11 patients with no SDH mutations. Compared with patients with SDHA-positive GISTs, those with SDHA-negative GISTs had an older median age (34 vs. 21 y), lower female to male ratio (1.8 vs. 3.1) but similar mitotic counts and median tumor sizes, with a slow course of disease in most cases, despite a slightly higher rate of liver metastases. SDHA-negative GISTs comprise approximately 30% of SDHB-negative/SDH-deficient GISTs, and SDHA loss generally correlates with SDHA mutations.

Loss of SDHA Expression Identifies SDHA Mutations in Succinate Dehydrogenase–deficient Gastrointestinal Stromal Tumors

Succinate dehydrogenase-deficient gastrointestinal stromal tumors (SDH-deficient GISTs) are a unique class of GIST defined by negative immunohistochemical staining for succinate dehydrogenase B (SDHB). SDH-deficient GISTs show distinctive clinical and pathologic features including absence of KIT and PDGFRA mutations, exclusive gastric location, common lymph node metastasis, a prognosis not predicted by size and mitotic rate, and indolent behavior of metastases. They may be syndromal with some being associated with the Carney Triad or germline SDHA, SDHB, SDHC, or SDHD mutations (Carney-Stratakis syndrome). It is normally recommended that genetic testing for SDHA, SDHB, SDHC, and SDHD be offered whenever an SDH-deficient GIST is encountered. However, testing for all 4 genes is burdensome and beyond the means of most centers. In this study we performed SDHA mutation and immunohistochemical analyses for SDHA on 10 SDH-deficient GISTs. Three showed negative staining for SDHA, and all of these were associated with germline SDHA mutations. In 2 tumors, 3 novel mutations were identified (p.Gln54X, p.Thr267Met, and c.1663+3G>C), none of which have previously been reported in GISTs or other SDH-associated tumors. Seven showed positive staining for SDHA and were not associated with SDHA mutation. In conclusion, 30% of SDH-deficient GISTs in this study were associated with germline SDHA mutation. Negative staining for SDHA can be used to triage formal genetic testing for SDHA when an SDH-deficient GIST is encountered.

Loss of expression of SDHA predicts SDHA mutations in gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are usually driven by mutations in KIT or PDGFRA, although 15% of GISTs in adults and >90% in children lack such mutations. The majority of gastric KIT/PDGFRA wild-type GISTs show distinctive morphological and clinical features and loss of expression of succinate dehydrogenase (SDH) B. Only a small subset of SDHB-deficient GISTs carries loss-of-function mutations in SDHB, SDHC, or SDHD. Because of the complexity of its locus (15 exons) and the presence of three pseudogenes, SDHA is rarely analyzed. Recently, mutations in SDHA were shown to lead to loss of expression of SDHA in a small group of paragangliomas. We sought to determine whether immunohistochemistry for SDHA could identify GISTs with SDHA mutations. Tumors (n=33) with pathological features of SDH-deficient GIST were analyzed for expression of SDHA and SDHB by immunohistochemistry, and SDHA exons were sequenced from tumors lacking SDHA expression. Exons harboring somatic mutations were examined in DNA from corresponding normal tissue. All 33 tumors showed loss of SDHB expression. A total of 9 out of 33 (27%) tumors also lacked expression of SDHA. SDHA-deficient GISTs affected five men and four women (median age 38 years). SDHA expression was intact in the 24 remaining tumors, including those with known SDHB (n=3) or SDHC (n=2) mutations. Nonsense (n=8) or missense (n=1) mutations in SDHA were identified in all SDHA-deficient tumors. Heterozygous mutations were also found in DNA from normal tissues from six patients with available material. Somatic loss of the second allele has been found in seven tumors, five by loss of heterozygosity, one by a 13-bp deletion, and one by a missense mutation. Loss of SDHA expression in GIST reliably predicts the presence of SDHA mutations, which represent a relatively common cause of SDH-deficient GIST in adults. Immunohistochemistry for SDHA can be used to select patients for SDHA-specific genetic testing.