Identification of eight novel SDHB, SDHC, SDHD germline variants in Danish pheochromocytoma/paraganglioma patients

Analytical Performance of NGS-Based Molecular Genetic Tests Used in the Diagnostic Workflow of Pheochromocytoma/Paraganglioma

Next Generation Sequencing (NGS)-based methods are high-throughput and cost-effective molecular genetic diagnostic tools. Targeted gene panel and whole exome sequencing (WES) are applied in clinical practice for assessing mutations of pheochromocytoma/paraganglioma (PPGL) associated genes, but the best strategy is debated. Germline mutations of at the least 18 PPGL genes are present in approximately 20-40% of patients, thus molecular genetic testing is recommended in all cases. We aimed to evaluate the analytical and clinical performances of NGS methods for mutation detection of PPGL-associated genes. WES (three different library preparation and bioinformatics workflows) and an in-house, hybridization based gene panel (endocrine-onco-gene-panel- ENDOGENE) was evaluated on 37 (20 WES and 17 ENDOGENE) samples with known variants. After optimization of the bioinformatic workflow, 61 additional samples were tested prospectively. All clinically relevant variants were validated with Sanger sequencing. Target capture of PPGL genes differed markedly between WES platforms and genes tested. All known variants were correctly identified by all methods, but methods of library preparations, sequencing platforms and bioinformatical settings significantly affected the diagnostic accuracy. The ENDOGENE panel identified several pathogenic mutations and unusual genotype-phenotype associations suggesting that the whole panel should be used for identification of genetic susceptibility of PPGL.

Succinate dehydrogenase deficient gastrointestinal stromal tumor in a three month old boy with a fatal clinical course: a case report and review of literature

Background

Succinate dehydrogenase deficient gastrointestinal stromal tumors (SDH-deficient GISTs), which lack KIT or PDGFRA mutations demonstrate unique clinical and pathological features, and they respond poorly to standard targeted therapy. We herein present a novel case of SDH-deficient GIST in a three-month-old infant’s colon mesentery, and he is the youngest patientto date.

Case presentation

The infantpresented with complaints of blood in the stool. CT showed a 6.3 × 4.6 cm mass in the left lower retroperitoneal. Complete resection of tumor and segmental bowel resection was performed without regional lymphadenectomy. Histologically, tumor cells were distinctive in their multinodular colon wall involvement with interspersed tracts of colon wall smooth muscle. The tumor was composed mainly of epithelioid cells. Immunohistochemically, the tumor cells were positive for Vim, CD117, PDGFR, while negative for SDHB. Mutational analysis showed a synonymous mutation for SDHB and wild-type for KIT and PDGFRA. Two months after surgery, metastases were found and Imatinib was administered. Unfortunately, the disease continued to progress, and the infant died 5 months after surgery.

Conclusions

SDH-deficient GISTs comprise a subgroup of a relatively rare tumor type and show a number of clinically and biologically unique features, especially for infants. It is of great importance to developing new therapeutic targets and novel specific drugs.

Germline RET Leu56Met Variant Is Likely Not Causative of Multiple Endocrine Neoplasia Type 2

Activating variants in the receptor tyrosine kinase REarranged during Transfection (RET) cause multiple endocrine neoplasia type 2 (MEN 2), an autosomal dominantly inherited cancer-susceptibility syndrome. The variant c.166C>A, p.Leu56Met in RET was recently reported in two patients with medullary thyroid cancer (MTC). The presence of a pheochromocytoma in one of the patients, suggested a possible pathogenic role of the variant in MEN 2A. Here, we present clinical follow up of a Danish RET Leu56Met cohort. Patients were evaluated for signs of MEN 2 according to a set of predefined criteria. None of the seven patients in our cohort exhibited evidence of MEN 2. Furthermore, we found the Leu56Met variant in our in-house diagnostic cohort with an allele frequency of 0.59%, suggesting that it is a common variant in the population. Additionally, none of the patients who harbored the allele were listed in the Danish MTC and MEN 2 registries. In conclusion, our findings do not support a pathogenic role of the Leu56Met variant in MEN 2.

Genotype-phenotype associations in PPGLs in 59 patients with variants in SDHX genes

Phaeochromocytomas and paragangliomas (PPGLs) are tumours of the adrenal medulla and extra-adrenal sympathetic nervous system which often secrete catecholamines. Variants of the SDHX (SDHA, -AF2, -B, -C, -D) genes are a frequent cause of familial PPGLs. In this study from a single tertiary centre, we aimed to characterise the genotype-phenotype associations in patients diagnosed with germline variants in SDHX genes. We also assessed whether systematic screening of family members resulted in earlier detection of tumours. The study cohort comprised all individuals (n = 59) diagnosed with a rare variant in SDHX during a 13-year period. Patient- and pathology records were checked for clinical characteristics and histopathological findings. We found distinct differences in the clinical and histopathological characteristics between genetic variants in SDHB. We identified two SDHB variants with distinct phenotypical patterns. Family screening for SDHB variants resulted in earlier detection of tumours in two families. Patients with SDHA, SDHC and SDHD variants also had malignant phenotypes, underlining the necessity for a broad genetic screening of the proband. Our study corroborates previous findings of poor prognostic markers and found that the genetic variants and clinical phenotype are linked and, therefore, useful in the decision of clinical follow-up. Regular tumour screening of carriers of pathogenic variants may lead to an earlier diagnosis and expected better prognosis. The development of a combined algorithm with clinical, genetic, morphological, and biochemical factors may be the future for improved clinical risk stratification, forming a basis for larger multi-centre follow up studies.

Molecular mechanism of mitochondrial respiratory chain assembly and its relation to mitochondrial diseases

The mitochondrial respiratory chain (MRC) is comprised of ~92 nuclear and mitochondrial DNA-encoded protein subunits that are organized into five different multi-subunit respiratory complexes. These complexes produce 90% of the ATP required for cell sustenance. Specific sets of subunits are assembled in a modular or non-modular fashion to construct the MRC complexes. The complete assembly process is gradually chaperoned by a myriad of assembly factors that must coordinate with several other prosthetic groups to reach maturity, makingthe entire processextensively complicated. Further, the individual respiratory complexes can be integrated intovarious giant super-complexes whose functional roles have yet to be explored. Mutations in the MRC subunits and in the related assembly factors often give rise to defects in the proper assembly of the respiratory chain, which then manifests as a group of disorders called mitochondrial diseases, the most common inborn errors of metabolism. This review summarizes the current understanding of the biogenesis of individual MRC complexes and super-complexes, and explores how mutations in the different subunits and assembly factors contribute to mitochondrial disease pathology.

Tumor-specific prognosis of mutation-positive patients with head and neck paragangliomas

BACKGROUND

Genetic testing to identify succinate dehydrogenase (SDH) mutations in patients with head and neck paraganglioma (HNP) has been in clinical practice for more than a decade. However, the recurrence and metachronous tumor occurrence risks in surgically treated mutation-positive patients are not well studied.

METHODS

Clinical and procedural details of consecutive patients who underwent excision for HNP from January 1996 to October 2016 were retrospectively reviewed. End points included recurrence, metachronous tumor detection, and mortality. Germline DNA was tested to identify mutations in SDHx genes. Patients were divided into three groups on the basis of genetic testing: group I, positive; group II, negative; and group III, unknown or offered but not tested.

RESULTS

HNP was diagnosed in 268 patients, 214 (147 female; mean age, 47 years) included in this study. Directed genetic testing was performed in 68; mutations were detected in SDH in 47 (69%), a majority SDHD. In group I, 47 patients had 64 procedures for 81 tumors (52 carotid body tumors [CBTs]); 17 (36%) were bilateral, 7 (15%) multiple, 3 (6%) functional, and 7 (15%) malignant. Residual tumor in 10 was significant in 2, managed by radiation therapy and reoperation. Local recurrence was detected in 12 patients (25%) at a median of 8 years; 11 metachronous mediastinal and retroperitoneal paragangliomas were detected in 8 (17%) at a median of 13 years. Systemic metastases occurred in five (10%). Six patients (13%) had more than one recurrence. In group II, 21 patients had 22 procedures for 23 tumors, 17 CBTs. Two (9%) were bilateral and two (9%) malignant. Excision was complete in all with no recurrence or systemic metastasis at last follow-up. For group III, 146 patients underwent 153 procedures for 156 tumors, 95 CBTs; 7 (5%) were bilateral, 2 (1%) multiple, 8 (5%) functional, and 1 (0.6%) malignant. Local recurrence was detected in nine (6%) at a median of 9 years and metachronous HNP in three (2%) at a median of 5 years. Systemic metastases occurred in two (1%). Mortality was 4% in group I and 3% in group III, none procedure or tumor related. Group I (mutation positive) had 10-year overall, recurrence-free, and metachronous tumor-free survival rates of 93%, 69.4%, and 73%, respectively, lower than the other groups (P < .001).

CONCLUSIONS

Bilateral, functional, malignant, recurrent, and metachronous tumors are more common in SDH mutation-positive patients with HNP. Overall survival in patients with HNP is high. Metachronous tumors or local recurrences occur late, and long-term follow-up is necessary.

Rescue of TCA Cycle Dysfunction for Cancer Therapy

Mitochondrion, a maternally hereditary, subcellular organelle, is the site of the tricarboxylic acid (TCA) cycle, electron transport chain (ETC), and oxidative phosphorylation (OXPHOS)—the basic processes of ATP production. Mitochondrial function plays a pivotal role in the development and pathology of different cancers. Disruption in its activity, like mutations in its TCA cycle enzymes, leads to physiological imbalances and metabolic shifts of the cell, which contributes to the progression of cancer. In this review, we explored the different significant mutations in the mitochondrial enzymes participating in the TCA cycle and the diseases, especially cancer types, that these malfunctions are closely associated with. In addition, this paper also discussed the different therapeutic approaches which are currently being developed to address these diseases caused by mitochondrial enzyme malfunction.

The loss of succinate dehydrogenase B expression is frequently identified in hemangioblastoma of the central nervous system

Succinate dehydrogenase (SDH) is a mitochondrial enzyme that plays an important role in both the Krebs cycle and the electron transport chain. SDH inactivation is associated with tumorigenesis in certain types of tumor. SDH consists of subunits A, B, C and D (SDHA, SDHB, SDHC, and SDHD, respectively). Immunohistochemistry for SDHB is a reliable method for detecting the inactivation of SDH by mutations in SDHA, SDHB, SDHC, SDHD and SDH complex assembly factor 2 (SDHAF2) genes with high sensitivity and specificity. SDHB immunohistochemistry has been used to examine the inactivation of SDH in various types of tumors. However, data on central nervous system (CNS) tumors are very limited. In the present study, we investigated the loss of SDHB immunoexpression in 90 cases of CNS tumors. Among the 90 cases of CNS tumors, only three cases of hemangioblastoma showed loss of SDHB immunoexpression. We further investigated SDHB immunoexpression in 35 cases of hemangioblastoma and found that 28 (80%) showed either negative or weak-diffuse pattern of SDHB immunoexpression, which suggests the inactivation of SDH. Our results suggest that SDH inactivation may represent an alternative pathway in the tumorigenesis of hemangioblastoma.

Extent of surgery for phaeochromocytomas in the genomic era

Background

Germline mutations are present in 20–30 per cent of patients with phaeochromocytoma. For patients who develop bilateral disease, complete removal of both adrenal glands (total adrenalectomy) will result in lifelong adrenal insufficiency with an increased risk of death from adrenal crisis. Unilateral/bilateral adrenal-sparing surgery (subtotal adrenalectomy) offers preservation of cortical function and independence from steroids, but leaves the adrenal medulla in situ and thus at risk of developing new and possibly malignant disease. Here, present knowledge about how tumour genotype relates to clinical behaviour is reviewed, and application of this knowledge when choosing the extent of adrenalectomy is discussed.

Methods

A literature review was undertaken of the penetrance of the different genotypes in phaeochromocytomas, the frequency of bilateral disease and malignancy, and the underlying pathophysiological mechanisms, with emphasis on explaining the clinical phenotypes of phaeochromocytomas and their associated syndromes.

Results

Patients with bilateral phaeochromocytomas most often have multiple endocrine neoplasia type 2 (MEN2) or von Hippel–Lindau disease (VHL) with high-penetrance mutations for benign disease, whereas patients with mutations in the genes encoding SDHB (succinate dehydrogenase subunit B) or MAX (myelocytomatosis viral proto-oncogene homologue-associated factor X) are at increased risk of malignancy.

Conclusion

Adrenal-sparing surgery should be the standard approach for patients who have already been diagnosed with MEN2 or VHL when operating on the first side, whereas complete removal of the affected adrenal gland(s) is generally recommended for patients with SDHB or MAX germline mutations. Routine assessment of a patient's genotype, even after the first operation, can be crucial for adopting an appropriate strategy for follow-up and future surgery.

Mitochondrial determinants of cancer health disparities

Mitochondria, which are multi-functional, have been implicated in cancer initiation, progression, and metastasis due to metabolic alterations in transformed cells. Mitochondria are involved in the generation of energy, cell growth and differentiation, cellular signaling, cell cycle control, and cell death. To date, the mitochondrial basis of cancer disparities is unknown. The goal of this review is to provide an understanding and a framework of mitochondrial determinants that may contribute to cancer disparities in racially different populations. Due to maternal inheritance and ethnic-based diversity, the mitochondrial genome (mtDNA) contributes to inherited racial disparities. In people of African ancestry, several germline, population-specific haplotype variants in mtDNA as well as depletion of mtDNA have been linked to cancer predisposition and cancer disparities. Indeed, depletion of mtDNA and mutations in mtDNA or nuclear genome (nDNA)-encoded mitochondrial proteins lead to mitochondrial dysfunction and promote resistance to apoptosis, the epithelial-to-mesenchymal transition, and metastatic disease, all of which can contribute to cancer disparity and tumor aggressiveness related to racial disparities. Ethnic differences at the level of expression or genetic variations in nDNA encoding the mitochondrial proteome, including mitochondria-localized mtDNA replication and repair proteins, miRNA, transcription factors, kinases and phosphatases, and tumor suppressors and oncogenes may underlie susceptibility to high-risk and aggressive cancers found in African population and other ethnicities. The mitochondrial retrograde signaling that alters the expression profile of nuclear genes in response to dysfunctional mitochondria is a mechanism for tumorigenesis. In ethnic populations, differences in mitochondrial function may alter the cross talk between mitochondria and the nucleus at epigenetic and genetic levels, which can also contribute to cancer health disparities. Targeting mitochondrial determinants and mitochondrial retrograde signaling could provide a promising strategy for the development of selective anticancer therapy for dealing with cancer disparities. Further, agents that restore mitochondrial function to optimal levels should permit sensitivity to anticancer agents for the treatment of aggressive tumors that occur in racially diverse populations and hence help in reducing racial disparities.

The emerging role and targetability of the TCA cycle in cancer metabolism

The tricarboxylic acid (TCA) cycle is a central route for oxidative phosphorylation in cells, and fulfills their bioenergetic, biosynthetic, and redox balance requirements. Despite early dogma that cancer cells bypass the TCA cycle and primarily utilize aerobic glycolysis, emerging evidence demonstrates that certain cancer cells, especially those with deregulated oncogene and tumor suppressor expression, rely heavily on the TCA cycle for energy production and macromolecule synthesis. As the field progresses, the importance of aberrant TCA cycle function in tumorigenesis and the potentials of applying small molecule inhibitors to perturb the enhanced cycle function for cancer treatment start to evolve. In this review, we summarize current knowledge about the fuels feeding the cycle, effects of oncogenes and tumor suppressors on fuel and cycle usage, common genetic alterations and deregulation of cycle enzymes, and potential therapeutic opportunities for targeting the TCA cycle in cancer cells. With the application of advanced technology and in vivo model organism studies, it is our hope that studies of this previously overlooked biochemical hub will provide fresh insights into cancer metabolism and tumorigenesis, subsequently revealing vulnerabilities for therapeutic interventions in various cancer types.