Mutant IDH1 inhibition induces dsDNA sensing to activate tumor immunity.

Isocitrate dehydrogenase 1 (IDH1) is the most commonly mutated metabolic gene across human cancers. Mutant IDH1 (mIDH1) generates the oncometabolite (R)-2-hydroxyglutarate, disrupting enzymes involved in epigenetics and other processes. A hallmark of IDH1-mutant solid tumors is T cell exclusion, whereas mIDH1 inhibition in preclinical models restores antitumor immunity. Here, we define a cell-autonomous mechanism of mIDH1-driven immune evasion. IDH1-mutant solid tumors show selective hypermethylation and silencing of the cytoplasmic double-stranded DNA (dsDNA) sensor CGAS, compromising innate immune signaling. mIDH1 inhibition restores DNA demethylation, derepressing CGAS and transposable element (TE) subclasses. dsDNA produced by TE-reverse transcriptase (TE-RT) activates cGAS, triggering viral mimicry and stimulating antitumor immunity. In summary, we demonstrate that mIDH1 epigenetically suppresses innate immunity and link endogenous RT activity to the mechanism of action of a US Food and Drug Administration-approved oncology drug.

Blockage of L2HGDH-mediated S-2HG catabolism orchestrates macrophage polarization to elicit antitumor immunity.

The high infiltration of tumor-associated macrophages (TAMs) in the immunosuppressive tumor microenvironment prominently attenuates the efficacy of immune checkpoint blockade (ICB) therapies, yet the underlying mechanisms are not fully understood. Here, we investigate the metabolic profile of TAMs and identify S-2-hydroxyglutarate (S-2HG) as a potential immunometabolite that shapes macrophages into an antitumoral phenotype. Blockage of L-2-hydroxyglutarate dehydrogenase (L2HGDH)-mediated S-2HG catabolism in macrophages promotes tumor regression. Mechanistically, based on its structural similarity to α-ketoglutarate (α-KG), S-2HG has the potential to block the enzymatic activity of 2-oxoglutarate-dependent dioxygenases (2-OGDDs), consequently reshaping chromatin accessibility. Moreover, S-2HG-treated macrophages enhance CD8+ T cell-mediated antitumor activity and sensitivity to anti-PD-1 therapy. Overall, our study uncovers the role of blockage of L2HGDH-mediated S-2HG catabolism in orchestrating macrophage antitumoral polarization and, further, provides the potential of repolarizing macrophages by S-2HG to overcome resistance to anti-PD-1 therapy.

Oncometabolite 2-hydroxyglutarate suppresses basal protein levels of DNA polymerase beta that enhances alkylating agent and PARG inhibition induced cytotoxicity.

Mutations in isocitrate dehydrogenase isoform 1 (IDH1) are primarily found in secondary glioblastoma (GBM) and low-grade glioma but are rare in primary GBM. The standard treatment for GBM includes radiation combined with temozolomide, an alkylating agent. Fortunately, IDH1 mutant gliomas are sensitive to this treatment, resulting in a more favorable prognosis. However, it's estimated that up to 75 % of IDH1 mutant gliomas will progress to WHO grade IV over time and develop resistance to alkylating agents. Therefore, understanding the mechanism(s) by which IDH1 mutant gliomas confer sensitivity to alkylating agents is crucial for developing targeted chemotherapeutic approaches. The base excision repair (BER) pathway is responsible for repairing most base damage induced by alkylating agents. Defects in this pathway can lead to hypersensitivity to these agents due to unresolved DNA damage. The coordinated assembly and disassembly of BER protein complexes are essential for cell survival and for maintaining genomic integrity following alkylating agent exposure. These complexes rely on poly-ADP-ribose formation, an NAD+-dependent post-translational modification synthesized by PARP1 and PARP2 during the BER process. At the lesion site, poly-ADP-ribose facilitates the recruitment of XRCC1. This scaffold protein helps assemble BER proteins like DNA polymerase beta (Polß), a bifunctional DNA polymerase containing both DNA synthesis and 5'-deoxyribose-phosphate lyase (5'dRP lyase) activity. Here, we confirm that IDH1 mutant glioma cells have defective NAD+ metabolism, but still produce sufficient nuclear NAD+ for robust PARP1 activation and BER complex formation in response to DNA damage. However, the overproduction of 2-hydroxyglutarate, an oncometabolite produced by the IDH1 R132H mutant protein, suppresses BER capacity by reducing Polß protein levels. This defines a novel mechanism by which the IDH1 mutation in gliomas confers cellular sensitivity to alkylating agents and to inhibitors of the poly-ADP-ribose glycohydrolase, PARG.

l-2-Hydroxyglutarate remodeling of the epigenome and epitranscriptome creates a metabolic vulnerability in kidney cancer models.

Tumor cells are known to undergo considerable metabolic reprogramming to meet their unique demands and drive tumor growth. At the same time, this reprogramming may come at a cost with resultant metabolic vulnerabilities. The small molecule l-2-hydroxyglutarate (l-2HG) is elevated in the most common histology of renal cancer. Similarly to other oncometabolites, l-2HG has the potential to profoundly impact gene expression. Here, we demonstrate that l-2HG remodels amino acid metabolism in renal cancer cells through combined effects on histone methylation and RNA N6-methyladenosine. The combined effects of l-2HG result in a metabolic liability that renders tumors cells reliant on exogenous serine to support proliferation, redox homeostasis, and tumor growth. In concert with these data, high-l-2HG kidney cancers demonstrate reduced expression of multiple serine biosynthetic enzymes. Collectively, our data indicate that high-l-2HG renal tumors could be specifically targeted by strategies that limit serine availability to tumors.

A multiomics approach reveals evidence for phenylbutyrate as a potential treatment for combined D,L-2- hydroxyglutaric aciduria.

PURPOSE: To identify therapies for combined D, L-2-hydroxyglutaric aciduria (C-2HGA), a rare genetic disorder caused by recessive variants in the SLC25A1 gene. METHODS: Patients C-2HGA were identified and diagnosed by whole exome sequencing and biochemical genetic testing. Patient derived fibroblasts were then treated with phenylbutyrate and the functional effects assessed by metabolomics and RNA-sequencing. RESULTS: In this study, we demonstrated that C-2HGA patient derived fibroblasts exhibited impaired cellular bioenergetics. Moreover, Fibroblasts form one patient exhibited worsened cellular bioenergetics when supplemented with citrate. We hypothesized that treating patient cells with phenylbutyrate (PB), an FDA approved pharmaceutical drug that conjugates glutamine for renal excretion, would reduce mitochondrial 2-ketoglutarate, thereby leading to improved cellular bioenergetics. Metabolomic and RNA-seq analyses of PB-treated fibroblasts demonstrated a significant decrease in intracellular 2-ketoglutarate, 2-hydroxyglutarate, and in levels of mRNA coding for citrate synthase and isocitrate dehydrogenase. Consistent with the known action of PB, an increased level of phenylacetylglutamine in patient cells was consistent with the drug acting as 2-ketoglutarate sink. CONCLUSION: Our pre-clinical studies suggest that citrate supplementation has the possibility exacerbating energy metabolism in this condition. However, improvement in cellular bioenergetics suggests phenylbutyrate might have interventional utility for this rare disease.

Rapid detection of IDH mutations in gliomas by intraoperative mass spectrometry.

The development and performance of two mass spectrometry (MS) workflows for the intraoperative diagnosis of isocitrate dehydrogenase (IDH) mutations in glioma is implemented by independent teams at Mayo Clinic, Jacksonville, and Huashan Hospital, Shanghai. The infiltrative nature of gliomas makes rapid diagnosis necessary to guide the extent of surgical resection of central nervous system (CNS) tumors. The combination of tissue biopsy and MS analysis used here satisfies this requirement. The key feature of both described methods is the use of tandem MS to measure the oncometabolite 2-hydroxyglutarate (2HG) relative to endogenous glutamate (Glu) to characterize the presence of mutant tumor. The experiments i) provide IDH mutation status for individual patients and ii) demonstrate a strong correlation of 2HG signals with tumor infiltration. The measured ratio of 2HG to Glu correlates with IDH-mutant (IDH-mut) glioma (P < 0.0001) in the tumor core data of both teams. Despite using different ionization methods and different mass spectrometers, comparable performance in determining IDH mutations from core tumor biopsies was achieved with sensitivities, specificities, and accuracies all at 100%. None of the 31 patients at Mayo Clinic or the 74 patients at Huashan Hospital were misclassified when analyzing tumor core biopsies. Robustness of the methodology was evaluated by postoperative re-examination of samples. Both teams noted the presence of high concentrations of 2HG at surgical margins, supporting future use of intraoperative MS to monitor for clean surgical margins. The power of MS diagnostics is shown in resolving contradictory clinical features, e.g., in distinguishing gliosis from IDH-mut glioma.

IDH1 mutation produces R-2-hydroxyglutarate (R-2HG) and induces mir-182-5p expression to regulate cell cycle and tumor formation in glioma.

BACKGROUND: Mutations in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2), are present in most gliomas. IDH1 mutation is an important prognostic marker in glioma. However, its regulatory mechanism in glioma remains incompletely understood. RESULTS: miR-182-5p expression was increased within IDH1-mutant glioma specimens according to TCGA, CGGA, and online dataset GSE119740, as well as collected clinical samples. (R)-2-hydroxyglutarate ((R)-2HG) treatment up-regulated the expression of miR-182-5p, enhanced glioma cell proliferation, and suppressed apoptosis; miR-182-5p inhibition partially eliminated the oncogenic effects of R-2HG upon glioma cells. By direct binding to Cyclin Dependent Kinase Inhibitor 2 C (CDKN2C) 3'UTR, miR-182-5p inhibited CDKN2C expression. Regarding cellular functions, CDKN2C knockdown promoted R-2HG-treated glioma cell viability, suppressed apoptosis, and relieved cell cycle arrest. Furthermore, CDKN2C knockdown partially attenuated the effects of miR-182-5p inhibition on cell phenotypes. Moreover, CDKN2C knockdown exerted opposite effects on cell cycle check point and apoptosis markers to those of miR-182-5p inhibition; also, CDKN2C knockdown partially attenuated the functions of miR-182-5p inhibition in cell cycle check point and apoptosis markers. The engineered CS-NPs (antagomir-182-5p) effectively encapsulated and delivered antagomir-182-5p, enhancing anti-tumor efficacy in vivo, indicating the therapeutic potential of CS-NPs(antagomir-182-5p) in targeting the miR-182-5p/CDKN2C axis against R-2HG-driven oncogenesis in mice models. CONCLUSIONS: These insights highlight the potential of CS-NPs(antagomir-182-5p) to target the miR-182-5p/CDKN2C axis, offering a promising therapeutic avenue against R-2HG's oncogenic influence to glioma.

[Research Progress of Isocitrate Dehydrogenase Mutation-Positive Acute Myeloid Leukemia --Review].

Isocitrate dehydrogenase (IDH) is an enzymes involved in a variety of metabolic and epigenetic processes. IDH can be detected in approximately 20% of patients with acute myeloid leukemia (AML), the mutated IDH enzyme acquires new oncogenic enzyme activity and converts α-ketoglutaric acid (α-KG) to the tumor metabolite 2-hydroxyglutaric acid (2-HG), which accumulates at high levels in cells and hinders the function of αKG-dependent enzymes, including epigenetic regulators, resulting in DNA hypermethylation, abnormal gene expression, cell proliferation, and abnormal differentiation, and contributes to leukemia disease progression. IDH mutations have different effects on the prognosis of patients with AML depending on the location of the mutation and other co-occurring genomic abnormalities. This paper will review the latest research progress on the IDH positive AML gene changes, prognosis, and inhibitors.

Molecular biology and novel therapeutics for IDH mutant gliomas: The new era of IDH inhibitors.

Gliomas with Isocitrate dehydrogenase (IDH) mutation represent a discrete category of primary brain tumors with distinct and unique characteristics, behaviors, and clinical disease outcomes. IDH mutations lead to aberrant high-level production of the oncometabolite D-2-hydroxyglutarate (D-2HG), which act as a competitive inhibitor of enzymes regulating epigenetics, signaling pathways, metabolism, and various other processes. This review summarizes the significance of IDH mutations, resulting upregulation of D-2HG and the associated molecular pathways in gliomagenesis. With the recent finding of clinically effective IDH inhibitors in these gliomas, this article offers a comprehensive overview of the new era of innovative therapeutic approaches based on mechanistic rationales, encompassing both completed and ongoing clinical trials targeting gliomas with IDH mutations.

Deciphering functional roles of protein succinylation and glutarylation using genetic code expansion.

Post-translational modifications (PTMs) dynamically regulate cellular processes. Lysine undergoes a range of acylations, including malonylation, succinylation (SucK) and glutarylation (GluK). These PTMs increase the size of the lysine side chain and reverse its charge from +1 to -1 under physiological conditions, probably impacting protein structure and function. To understand the functional roles of these PTMs, homogeneously modified proteins are required for biochemical studies. While the site-specific encoding of PTMs and their mimics via genetic code expansion has facilitated the characterization of the functional roles of many PTMs, negatively charged lysine acylations have defied this approach. Here we describe site-specific incorporation of SucK and GluK into proteins via temporarily masking their negative charge through thioester derivatives. We prepare succinylated and glutarylated bacterial and mammalian target proteins, including non-refoldable multidomain proteins. This allows us to study how succinylation and glutarylation impact enzymatic activity of metabolic enzymes and regulate protein-DNA and protein-protein interactions in biological processes from replication to ubiquitin signalling.

Systems engineering of Escherichia coli for high-level glutarate production from glucose.

Glutarate is a key monomer in polyester and polyamide production. The low efficiency of the current biosynthetic pathways hampers its production by microbial cell factories. Herein, through metabolic simulation, a lysine-overproducing E. coli strain Lys5 is engineered, achieving titer, yield, and productivity of 195.9 g/L, 0.67 g/g glucose, and 5.4 g/L·h, respectively. Subsequently, the pathway involving aromatic aldehyde synthase, monoamine oxidase, and aldehyde dehydrogenase (AMA pathway) is introduced into E. coli Lys5 to produce glutarate from glucose. To enhance the pathway's efficiency, rational mutagenesis on the aldehyde dehydrogenase is performed, resulting in the development of variant Mu5 with a 50-fold increase in catalytic efficiency. Finally, a glutarate tolerance gene cbpA is identified and genomically overexpressed to enhance glutarate productivity. With enzyme expression optimization, the glutarate titer, yield, and productivity of E. coli AMA06 reach 88.4 g/L, 0.42 g/g glucose, and 1.8 g/L·h, respectively. These findings hold implications for improving glutarate biosynthesis efficiency in microbial cell factories.

Isocitrate Dehydrogenase Mutations in Cancer: Mechanisms of Transformation and Metabolic Liability.

Isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) are metabolic enzymes that interconvert isocitrate and 2-oxoglutarate (2OG). Gain-of-function mutations in IDH1 and IDH2 occur in a number of cancers, including acute myeloid leukemia, glioma, cholangiocarcinoma, and chondrosarcoma. These mutations cripple the wild-type activity of IDH and cause the enzymes to catalyze a partial reverse reaction in which 2OG is reduced but not carboxylated, resulting in production of the (R)-enantiomer of 2-hydroxyglutarate ((R)-2HG). (R)-2HG accumulation in IDH-mutant tumors results in profound dysregulation of cellular metabolism. The most well-characterized oncogenic effects of (R)-2HG involve the dysregulation of 2OG-dependent epigenetic tumor-suppressor enzymes. However, (R)-2HG has many other effects in IDH-mutant cells, some that promote transformation and others that induce metabolic dependencies. Herein, we review how cancer-associated IDH mutations impact epigenetic regulation and cellular metabolism and discuss how these effects can potentially be leveraged to therapeutically target IDH-mutant tumors.

Structure and biochemical characterization of l-2-hydroxyglutarate dehydrogenase and its role in the pathogenesis of l-2-hydroxyglutaric aciduria.

l-2-hydroxyglutarate dehydrogenase (L2HGDH) is a mitochondrial membrane-associated metabolic enzyme, which catalyzes the oxidation of l-2-hydroxyglutarate (l-2-HG) to 2-oxoglutarate (2-OG). Mutations in human L2HGDH lead to abnormal accumulation of l-2-HG, which causes a neurometabolic disorder named l-2-hydroxyglutaric aciduria (l-2-HGA). Here, we report the crystal structures of Drosophila melanogaster L2HGDH (dmL2HGDH) in FAD-bound form and in complex with FAD and 2-OG and show that dmL2HGDH exhibits high activity and substrate specificity for l-2-HG. dmL2HGDH consists of an FAD-binding domain and a substrate-binding domain, and the active site is located at the interface of the two domains with 2-OG binding to the re-face of the isoalloxazine moiety of FAD. Mutagenesis and activity assay confirmed the functional roles of key residues involved in the substrate binding and catalytic reaction and showed that most of the mutations of dmL2HGDH equivalent to l-2-HGA-associated mutations of human L2HGDH led to complete loss of the activity. The structural and biochemical data together reveal the molecular basis for the substrate specificity and catalytic mechanism of L2HGDH and provide insights into the functional roles of human L2HGDH mutations in the pathogeneses of l-2-HGA.

The two enantiomers of 2-hydroxyglutarate differentially regulate cytotoxic T cell function.

2-Hydroxyglutarate (2HG) is a byproduct of the tricarboxylic acid (TCA) cycle and is readily detected in the tissues of healthy individuals. 2HG is found in two enantiomeric forms: S-2HG and R-2HG. Here, we investigate the differential roles of these two enantiomers in cluster of differentiation (CD)8+ T cell biology, where we find they have highly divergent effects on proliferation, differentiation, and T cell function. We show here an analysis of structural determinants that likely underlie these differential effects on specific α-ketoglutarate (αKG)-dependent enzymes. Treatment of CD8+ T cells with exogenous S-2HG, but not R-2HG, increased CD8+ T cell fitness in vivo and enhanced anti-tumor activity. These data show that S-2HG and R-2HG should be considered as two distinct and important actors in the regulation of T cell function.

Glutarate regulates T cell metabolism and anti-tumour immunity.

T cell function and fate can be influenced by several metabolites: in some cases, acting through enzymatic inhibition of α-ketoglutarate-dependent dioxygenases, in others, through post-translational modification of lysines in important targets. We show here that glutarate, a product of amino acid catabolism, has the capacity to do both, and has potent effects on T cell function and differentiation. We found that glutarate exerts those effects both through α-ketoglutarate-dependent dioxygenase inhibition, and through direct regulation of T cell metabolism via glutarylation of the pyruvate dehydrogenase E2 subunit. Administration of diethyl glutarate, a cell-permeable form of glutarate, alters CD8+ T cell differentiation and increases cytotoxicity against target cells. In vivo administration of the compound is correlated with increased levels of both peripheral and intratumoural cytotoxic CD8+ T cells. These results demonstrate that glutarate is an important regulator of T cell metabolism and differentiation with a potential role in the improvement of T cell immunotherapy.

Nrf2 sensitizes ferroptosis through l-2-hydroxyglutarate-mediated chromatin modifications in sickle cell disease.

Sickle cell disease (SCD) is a chronic hemolytic and systemic hypoxia condition with constant oxidative stress and significant metabolic alterations. However, little is known about the correlation between metabolic alterations and the pathophysiological symptoms. Here, we report that Nrf2, a master regulator of cellular antioxidant responses, regulates the production of the metabolite l-2-hydroxyglutarate (L2HG) to mediate epigenetic histone hypermethylation for gene expression involved in metabolic, oxidative, and ferroptotic stress responses in SCD. Mechanistically, Nrf2 was found to regulate the expression of L2HG dehydrogenase (L2hgdh) to mediate L2HG production under hypoxia. Gene expression profile analysis indicated that reactive oxygen species (ROS) and ferroptosis responses were the most significantly affected signaling pathways after Nrf2 ablation in SCD. Nrf2 silencing and L2HG supplementation sensitize human sickle erythroid cells to ROS and ferroptosis stress. The absence of Nrf2 and accumulation of L2HG significantly affect histone methylation for chromatin structure modification and reduce the assembly of transcription complexes on downstream target genes to regulate ROS and ferroptosis responses. Furthermore, pharmacological activation of Nrf2 was found to have protective effects against ROS and ferroptosis stress in SCD mice. Our data suggest a novel mechanism by which Nrf2 regulates L2HG levels to mediate SCD severity through ROS and ferroptosis stress responses, suggesting that targeting Nrf2 is a viable therapeutic strategy for ameliorating SCD symptoms.

Phenotypic prediction in glutaric aciduria type 1 combining in silico and in vitro modeling with real-world data.

Glutaric aciduria type 1 (GA1) is caused by inherited deficiency of glutaryl-CoA dehydrogenase (GCDH). To further understand the unclear genotype-phenotype correlation, we transfected mutated GCDH into COS-7 cells resembling known biallelic GCDH variants of 47 individuals with GA1. In total, we modeled 36 genotypes with 32 missense variants. Spectrophotometry demonstrated an inverse correlation between residual enzyme activity and the urinary concentration of glutaric acid and 3-hydroxyglutaric acid, confirming previous studies (Pearson correlation, r = -0.34 and r = -0.49, p = 0.045 and p = 0.002, respectively). In silico modeling predicted high pathogenicity for all genotypes, which caused a low enzyme activity. Western blotting revealed a 2.6-times higher GCDH protein amount in patients with an acute encephalopathic crisis (t-test, p = 0.015), and high protein expression correlated with high in silico protein stability (Pearson correlation, r = -0.42, p = 0.011). The protein amount was not correlated with the enzyme activity (Pearson correlation, r = 0.09, p = 0.59). To further assess protein stability, proteolysis was performed, showing that the p.Arg88Cys variant stabilized a heterozygous less stable variant. We conclude that an integration of different data sources helps to predict the complex clinical phenotype in individuals with GA1.

Efficient bio-production of glutaric acid by a metabolically engineered Escherichia coli LQ-1 based on a novel nitrogen source feeding strategy.

As an important five-carbon platform chemical to synthesize polyesters and polyamides, glutaric acid is widely used in numerous biochemical fields such as consumer goods, textile, and footwear industries. However, the application of glutaric acid is limited by the low yield of its bio-production. In this study, a metabolically engineered Escherichia coli LQ-1 based on 5-aminovalerate (AMV) pathway was used for glutaric acid fed-batch fermentation. Given the significance of nitrogen source in the bio-production of glutaric acid by AMV pathway, a novel nitrogen source feeding strategy feedbacked by real-time physiological parameters was proposed after evaluating the effects of nitrogen source feeding (such as ammonia and ammonium sulfate) on glutaric acid bio-production. Under the proposed nitrogen source feeding strategy, a significantly improved glutaric acid production of 53.7 g L-1 was achieved in a 30 L fed-batch fermentation by the metabolically engineered E. coli LQ-1, which was an improvement of 52.1% over pre-optimization. Additionally, a higher conversion rate of 0.64 mol mol-1 (glutaric acid/glucose) was obtained compared with the previously reported bio-production of glutaric acid with E. coli. These results indicated that the nitrogen source feeding strategy proposed in this study will be useful for achieving the efficient and sustainable bio-based production of glutaric acid.

Exceptionally rare IDH1-mutant adult medulloblastoma with concurrent GNAS mutation revealed by in vivo magnetic resonance spectroscopy and deep sequencing.

Medulloblastoma (MB) is the most common malignant brain tumor occurring in childhood and rarely found in adults. Based on transcriptome profile, MB are currently classified into four major molecular groups reflecting a considerable biological heterogeneity: WNT-activated, SHH-activated, group 3 and group 4. Recently, DNA methylation profiling allowed the identification of additional subgroups within the four major molecular groups associated with different clinic-pathological and molecular features. Isocitrate dehydrogenase-1 and 2 (IDH1 and IDH2) mutations have been described in several tumors, including gliomas, while in MB are rarely reported and not routinely investigated. By means of magnetic resonance spectroscopy (MRS), we unequivocally assessed the presence the oncometabolite D-2-hydroxyglutarate (2HG), a marker of IDH1 and IDH2 mutations, in a case of adult MB. Immunophenotypical work-up and methylation profiling assigned the diagnosis of MB, subclass SHH-A, and molecular testing revealed the presence of the non-canonical somatic IDH1(p.R132C) mutation and an additional GNAS mutation, also rarely described in MB. To the best of our knowledge, this is the first reported case of MB simultaneously harboring both mutations. Of note, tumor exhibited a heterogeneous phenotype with a tumor component displaying glial differentiation, with robust GFAP expression, and a component with conventional MB features and selective presence of GNAS mutation, suggesting co-existence of two different major tumor subclones. These findings drew attention to the need for a deeper genetic characterization of MB, in order to get insights into their biology and improve stratification and clinical management of the patients. Moreover, our results underlined the importance of performing MRS for the identification of IDH mutations in non-glial tumors. The use of throughput molecular profiling analysis and advanced medical imaging will certainly increase the frequency with which tumor entities with rare molecular alterations will be identified. Whether these findings have any specific therapeutic implications or prognostic relevance requires further investigations.

Recommendations for diagnosing and managing individuals with glutaric aciduria type 1: Third revision.

Glutaric aciduria type 1 is a rare inherited neurometabolic disorder of lysine metabolism caused by pathogenic gene variations in GCDH (cytogenic location: 19p13.13), resulting in deficiency of mitochondrial glutaryl-CoA dehydrogenase (GCDH) and, consequently, accumulation of glutaric acid, 3-hydroxyglutaric acid, glutaconic acid and glutarylcarnitine detectable by gas chromatography/mass spectrometry (organic acids) and tandem mass spectrometry (acylcarnitines). Depending on residual GCDH activity, biochemical high and low excreting phenotypes have been defined. Most untreated individuals present with acute onset of striatal damage before age 3 (to 6) years, precipitated by infectious diseases, fever or surgery, resulting in irreversible, mostly dystonic movement disorder with limited life expectancy. In some patients, striatal damage develops insidiously. In recent years, the clinical phenotype has been extended by the finding of extrastriatal abnormalities and cognitive dysfunction, preferably in the high excreter group, as well as chronic kidney failure. Newborn screening is the prerequisite for pre-symptomatic start of metabolic treatment with low lysine diet, carnitine supplementation and intensified emergency treatment during catabolic episodes, which, in combination, have substantially improved neurologic outcome. In contrast, start of treatment after onset of symptoms cannot reverse existing motor dysfunction caused by striatal damage. Dietary treatment can be relaxed after the vulnerable period for striatal damage, that is, age 6 years. However, impact of dietary relaxation on long-term outcomes is still unclear. This third revision of evidence-based recommendations aims to re-evaluate previous recommendations (Boy et al., J Inherit Metab Dis, 2017;40(1):75-101; Kolker et al., J Inherit Metab Dis 2011;34(3):677-694; Kolker et al., J Inherit Metab Dis, 2007;30(1):5-22) and to implement new research findings on the evolving phenotypic diversity as well as the impact of non-interventional variables and treatment quality on clinical outcomes.