Publications by authors named "Richard J Rodenburg"

169 Publications

Exome sequencing in paediatric patients with movement disorders.

Orphanet J Rare Dis 2021 Jan 15;16(1):32. Epub 2021 Jan 15.

Department of Paediatrics and Adolescent Medicine, LKS Faculty of Medicine, The University of Hong Kong, Pok Fu Lam, Hong Kong SAR, China.

Background: Movement disorders are a group of heterogeneous neurological diseases including hyperkinetic disorders with unwanted excess movements and hypokinetic disorders with reduction in the degree of movements. The objective of our study is to investigate the genetic etiology of a cohort of paediatric patients with movement disorders by whole exome sequencing and to review the potential treatment implications after a genetic diagnosis.

Results: We studied a cohort of 31 patients who have paediatric-onset movement disorders with unrevealing etiologies. Whole exome sequencing was performed and rare variants were interrogated for pathogenicity. Genetic diagnoses have been confirmed in 10 patients with disease-causing variants in CTNNB1, SPAST, ATP1A3, PURA, SLC2A1, KMT2B, ACTB, GNAO1 and SPG11. 80% (8/10) of patients with genetic diagnosis have potential treatment implications and treatments have been offered to them. One patient with KMT2B dystonia showed clinical improvement with decrease in dystonia after receiving globus pallidus interna deep brain stimulation.

Conclusions: A diagnostic yield of 32% (10/31) was reported in our cohort and this allows a better prediction of prognosis and contributes to a more effective clinical management. The study highlights the potential of implementing precision medicine in the patients.
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http://dx.doi.org/10.1186/s13023-021-01688-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7809769PMC
January 2021

One mutation, three phenotypes: novel metabolic insights on MELAS, MIDD and myopathy caused by the m.3243A > G mutation.

Metabolomics 2021 01 12;17(1):10. Epub 2021 Jan 12.

Mitochondria Research Laboratory, Human Metabolomics, North-West University, Potchefstroom, South Africa.

Introduction: The m.3243A > G mitochondrial DNA mutation is one of the most common mitochondrial disease-causing mutations, with a carrier rate as high as 1:400. This point mutation affects the MT-TL1 gene, ultimately affecting the oxidative phosphorylation system and the cell's energy production. Strikingly, the m.3243A > G mutation is associated with different phenotypes, including mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS), maternally inherited diabetes and deafness (MIDD) and myopathy.

Objectives: We investigated urine metabolomes of MELAS, MIDD and myopathy patients in order to identify affected metabolic pathways and possible treatment options.

Methods: A multiplatform metabolomics approach was used to comprehensively analyze the metabolome and compare metabolic profiles of different phenotypes caused by the m.3243A > G mutation. Our analytical array consisted of NMR spectroscopy, LC-MS/MS and GC-TOF-MS.

Results: The investigation revealed phenotypic specific metabolic perturbations, as well as metabolic similarities between the different phenotypes. We show that glucose metabolism is highly disturbed in the MIDD phenotype, but not in MELAS or myopathy, remodeled fatty acid oxidation is characteristic of the MELAS patients, while one-carbon metabolism is strongly modified in both MELAS and MIDD, but not in the myopathy group. Lastly we identified increased creatine in the urine of the myopathy patients, but not in MELAS or MIDD.

Conclusion: We conclude by giving novel insight on the phenotypes of the m.3243A > G mutation from a metabolomics point of view. Directives are also given for future investigations that could lead to better treatment options for patients suffering from this debilitating disease.
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http://dx.doi.org/10.1007/s11306-020-01769-wDOI Listing
January 2021

Soluble adenylyl cyclase regulates the cytosolic NADH/NAD redox state and the bioenergetic switch between glycolysis and oxidative phosphorylation.

Biochim Biophys Acta Bioenerg 2021 Apr 5;1862(4):148367. Epub 2021 Jan 5.

Tytgat Institute for Liver and Intestinal Research, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands; Amsterdam Gastroenterology Endocrinology Metabolism (AGEM) Research Institute, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands.

The evolutionarily conserved soluble adenylyl cyclase (sAC, ADCY10) mediates cAMP signaling exclusively in intracellular compartments. Because sAC activity is sensitive to local concentrations of ATP, bicarbonate, and free Ca, sAC is potentially an important metabolic sensor. Nonetheless, little is known about how sAC regulates energy metabolism in intact cells. In this study, we demonstrated that both pharmacological and genetic suppression of sAC resulted in increased lactate secretion and decreased pyruvate secretion in multiple cell lines and primary cultures of mouse hepatocytes and cholangiocytes. The increased extracellular lactate-to-pyruvate ratio upon sAC suppression reflected an increased cytosolic free [NADH]/[NAD] ratio, which was corroborated by using the NADH/NAD redox biosensor Peredox-mCherry. Mechanistic studies in permeabilized HepG2 cells showed that sAC inhibition specifically suppressed complex I of the mitochondrial respiratory chain. A survey of cAMP effectors revealed that only selective inhibition of exchange protein activated by cAMP 1 (Epac1), but not protein kinase A (PKA) or Epac2, suppressed complex I-dependent respiration and significantly increased the cytosolic NADH/NAD redox state. Analysis of the ATP production rate and the adenylate energy charge showed that inhibiting sAC reciprocally affects ATP production by glycolysis and oxidative phosphorylation while maintaining cellular energy homeostasis. In conclusion, our study shows that, via the regulation of complex I-dependent mitochondrial respiration, sAC-Epac1 signaling regulates the cytosolic NADH/NAD redox state, and coordinates oxidative phosphorylation and glycolysis to maintain cellular energy homeostasis. As such, sAC is effectively a bioenergetic switch between aerobic glycolysis and oxidative phosphorylation at the post-translational level.
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http://dx.doi.org/10.1016/j.bbabio.2020.148367DOI Listing
April 2021

A novel variant in COX16 causes cytochrome c oxidase deficiency, severe fatal neonatal lactic acidosis, encephalopathy, cardiomyopathy, and liver dysfunction.

Hum Mutat 2021 Feb 30;42(2):135-141. Epub 2020 Nov 30.

Department of Laboratory Medicine, Translational Metabolic Laboratory, Radboud Centre for Mitochondrial Medicine, Radboudumc, Nijmegen, The Netherlands.

COX16 is involved in the biogenesis of cytochrome-c-oxidase (complex IV), the terminal complex of the mitochondrial respiratory chain. We present the first report of two unrelated patients with the homozygous nonsense variant c.244C>T(p. Arg82*) in COX16 with hypertrophic cardiomyopathy, encephalopathy and severe fatal lactic acidosis, and isolated complex IV deficiency. The absence of COX16 protein expression leads to a complete loss of the holo-complex IV, as detected by Western blot in patient fibroblasts. Lentiviral transduction of patient fibroblasts with wild-type COX16 complementary DNA rescued complex IV biosynthesis. We hypothesize that COX16 could play a role in the copper delivery route of the COX2 module as part of the complex IV assembly. Our data provide clear evidence for the pathogenicity of the COX16 variant as a cause for the observed clinical features and the isolated complex IV deficiency in these two patients and that COX16 deficiency is a cause for mitochondrial disease.
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http://dx.doi.org/10.1002/humu.24137DOI Listing
February 2021

Loss of sdhb in zebrafish larvae recapitulates human paraganglioma characteristics.

Endocr Relat Cancer 2021 Jan;28(1):65-77

Department of Internal Medicine, Radboud University Medical Center, Nijmegen, the Netherlands.

Pheochromocytomas and paragangliomas (PPGLs) caused by mutations in the B-subunit of the succinate dehydrogenase (SDHB) have the highest metastatic rate among PPGLs, and effective systemic therapy is lacking. To unravel underlying pathogenic mechanisms, and to evaluate therapeutic strategies, suitable in vivo models are needed. The available systemic Sdhb knock-out mice cannot model the human PPGL phenotype: heterozygous Sdhb mice lack a disease phenotype, and homozygous Sdhb mice are embryonically lethal. Using CRISPR/cas9 technology, we introduced a protein-truncating germline lesion into the zebrafish sdhb gene. Heterozygous sdhb mutants were viable and displayed no obvious morphological or developmental defects. Homozygous sdhb larvae were viable, but exhibited a decreased lifespan. Morphological analysis revealed incompletely or non-inflated swim bladders in homozygous sdhb mutants at day 6. Although no differences in number and ultrastructure of the mitochondria were observed. Clear defects in energy metabolism and swimming behavior were observed in homozygous sdhb mutant larvae. Functional and metabolomic analyses revealed decreased mitochondrial complex 2 activity and significant succinate accumulation in the homozygous sdhb mutant larvae, mimicking the metabolic effects observed in SDHB-associated PPGLs. This is the first study to present a vertebrate animal model that mimics metabolic effects of SDHB-associated PPGLs. This model will be useful in unraveling pathomechanisms behind SDHB-associated PPGLs. We can now study the metabolic effects of sdhb disruption during different developmental stages and develop screening assays to identify novel therapeutic targets in vivo. Besides oncological syndromes, our model might also be useful for pediatric mitochondrial disease caused by loss of the SDHB gene.
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http://dx.doi.org/10.1530/ERC-20-0308DOI Listing
January 2021

Delineation of molecular findings by whole-exome sequencing for suspected cases of paediatric-onset mitochondrial diseases in the Southern Chinese population.

Hum Genomics 2020 09 10;14(1):28. Epub 2020 Sep 10.

Department of Paediatrics & Adolescent Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong, SAR, China.

Background: Mitochondrial diseases (MDs) are a group of clinically and genetically heterogeneous disorders characterized by defects in oxidative phosphorylation. Since clinical phenotypes of MDs may be non-specific, genetic diagnosis is crucial for guiding disease management. In the current study, whole-exome sequencing (WES) was performed for our paediatric-onset MD cohort of a Southern Chinese origin, with the aim of identifying key disease-causing variants in the Chinese patients with MDs.

Methods: We recruited Chinese patients who had paediatric-onset MDs and a minimum mitochondrial disease criteria (MDC) score of 3. Patients with positive target gene or mitochondrial DNA sequencing results were excluded. WES was performed, variants with population frequency ≤ 1% were analysed for pathogenicity on the basis of the American College of Medical Genetics and Genomics guidelines.

Results: Sixty-six patients with pre-biopsy MDC scores of 3-8 were recruited. The overall diagnostic yield was 35% (23/66). Eleven patients (17%) were found to have mutations in MD-related genes, with COQ4 having the highest mutation rate owing to the Chinese-specific founder mutation (4/66, 6%). Twelve patients (12/66, 18%) had mutations in non-MD-related genes: ATP1A3 (n = 3, two were siblings), ALDH5A1, ARX, FA2H, KCNT1, LDHD, NEFL, NKX2-2, TBCK, and WAC.

Conclusions: We confirmed that the COQ4:c.370G>A, p.(Gly124Ser) variant, was a founder mutation among the Southern Chinese population. Screening for this mutation should therefore be considered while diagnosing Chinese patients suspected to have MDs. Furthermore, WES has proven to be useful in detecting variants in patients suspected to have MDs because it helps to obtain an unbiased and precise genetic diagnosis for these diseases, which are genetically heterogeneous.
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http://dx.doi.org/10.1186/s40246-020-00278-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7488033PMC
September 2020

Chronic fluoxetine or ketamine treatment differentially affects brain energy homeostasis which is not exacerbated in mice with trait suboptimal mitochondrial function.

Eur J Neurosci 2020 Jul 9. Epub 2020 Jul 9.

Department of Anatomy, Donders Institute for Brain Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The Netherlands.

Antidepressants have been shown to influence mitochondrial function directly, and suboptimal mitochondrial function (SMF) has been implicated in complex psychiatric disorders. In the current study, we used a mouse model for trait SMF to test the hypothesis that chronic fluoxetine treatment in mice subjected to chronic stress would negatively impact brain bioenergetics, a response that would be more pronounced in mice with trait SMF. In contrast, we hypothesized that chronic ketamine treatment would positively impact mitochondrial function in both WT and mice with SMF. We used an animal model for trait SMF, the Ndufs4 mice, which exhibit 25% lower mitochondrial complex I activity. In addition to antidepressant treatment, mice were subjected to chronic unpredictable stress (CUS). This paradigm is widely used to model complex behaviours expressed in various psychiatric disorders. We assayed several physiological indices as proxies for the impact of chronic stress and antidepressant treatment. Furthermore, we measured brain mitochondrial complex activities using clinically validated assays as well as established metabolic signatures using targeted metabolomics. As hypothesized, we found evidence that chronic fluoxetine treatment negatively impacted brain bioenergetics. This phenotype was, however, not further exacerbated in mice with trait SMF. Ketamine did not have a significant influence on brain mitochondrial function in either genotype. Here we report that trait SMF could be a moderator for an individual's response to antidepressant treatment. Based on these results, we propose that in individuals with SMF and comorbid psychopathology, fluoxetine should be avoided, whereas ketamine could be a safer choice of treatment.
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http://dx.doi.org/10.1111/ejn.14901DOI Listing
July 2020

Impaired mitochondrial complex I function as a candidate driver in the biological stress response and a concomitant stress-induced brain metabolic reprogramming in male mice.

Transl Psychiatry 2020 06 1;10(1):176. Epub 2020 Jun 1.

Department of Anatomy, Radboud University Medical Center, Donders Institute for Brain Cognition and Behaviour, Nijmegen, The Netherlands.

Mitochondria play a critical role in bioenergetics, enabling stress adaptation, and therefore, are central in biological stress responses and stress-related complex psychopathologies. To investigate the effect of mitochondrial dysfunction on the stress response and the impact on various biological domains linked to the pathobiology of depression, a novel mouse model was created. These mice harbor a gene trap in the first intron of the Ndufs4 gene (Ndufs4 mice), encoding the NDUFS4 protein, a structural component of complex I (CI), the first enzyme of the mitochondrial electron transport chain. We performed a comprehensive behavioral screening with a broad range of behavioral, physiological, and endocrine markers, high-resolution ex vivo brain imaging, brain immunohistochemistry, and multi-platform targeted mass spectrometry-based metabolomics. Ndufs4 mice presented with a 25% reduction of CI activity in the hippocampus, resulting in a relatively mild phenotype of reduced body weight, increased physical activity, decreased neurogenesis and neuroinflammation compared to WT littermates. Brain metabolite profiling revealed characteristic biosignatures discriminating Ndufs4 from WT mice. Specifically, we observed a reversed TCA cycle flux and rewiring of amino acid metabolism in the prefrontal cortex. Next, exposing mice to chronic variable stress (a model for depression-like behavior), we found that Ndufs4 mice showed altered stress response and coping strategies with a robust stress-associated reprogramming of amino acid metabolism. Our data suggest that impaired mitochondrial CI function is a candidate driver for altered stress reactivity and stress-induced brain metabolic reprogramming. These changes result in unique phenomic and metabolomic signatures distinguishing groups based on their mitochondrial genotype.
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http://dx.doi.org/10.1038/s41398-020-0858-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7266820PMC
June 2020

NDUFS4 deletion triggers loss of NDUFA12 in Ndufs4 mice and Leigh syndrome patients: A stabilizing role for NDUFAF2.

Biochim Biophys Acta Bioenerg 2020 08 23;1861(8):148213. Epub 2020 Apr 23.

Department of Biochemistry, Radboud Institute for Molecular Life Sciences, Radboud Center for Mitochondrial Medicine, Radboudumc, Nijmegen, the Netherlands. Electronic address:

Mutations in NDUFS4, which encodes an accessory subunit of mitochondrial oxidative phosphorylation (OXPHOS) complex I (CI), induce Leigh syndrome (LS). LS is a poorly understood pediatric disorder featuring brain-specific anomalies and early death. To study the LS pathomechanism, we here compared OXPHOS proteomes between various Ndufs4 mouse tissues. Ndufs4 animals displayed significantly lower CI subunit levels in brain/diaphragm relative to other tissues (liver/heart/kidney/skeletal muscle), whereas other OXPHOS subunit levels were not reduced. Absence of NDUFS4 induced near complete absence of the NDUFA12 accessory subunit, a 50% reduction in other CI subunit levels, and an increase in specific CI assembly factors. Among the latter, NDUFAF2 was most highly increased. Regarding NDUFS4, NDUFA12 and NDUFAF2, identical results were obtained in Ndufs4 mouse embryonic fibroblasts (MEFs) and NDUFS4-mutated LS patient cells. Ndufs4 MEFs contained active CI in situ but blue-native-PAGE highlighted that NDUFAF2 attached to an inactive CI subcomplex (CI-830) and inactive assemblies of higher MW. In NDUFA12-mutated LS patient cells, NDUFA12 absence did not reduce NDUFS4 levels but triggered NDUFAF2 association to active CI. BN-PAGE revealed no such association in LS patient fibroblasts with mutations in other CI subunit-encoding genes where NDUFAF2 was attached to CI-830 (NDUFS1, NDUFV1 mutation) or not detected (NDUFS7 mutation). Supported by enzymological and CI in silico structural analysis, we conclude that absence of NDUFS4 induces near complete absence of NDUFA12 but not vice versa, and that NDUFAF2 stabilizes active CI in Ndufs4 mice and LS patient cells, perhaps in concert with mitochondrial inner membrane lipids.
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http://dx.doi.org/10.1016/j.bbabio.2020.148213DOI Listing
August 2020

Clinical, morphological and genetic characterization of Brody disease: an international study of 40 patients.

Brain 2020 02;143(2):452-466

Assistance Publique-Hôpitaux de Paris, Centre de Référence des Canalopathies Musculaires, Centre de Référence des Maladies Neuromusculaires-Paris Est et Service de Génétique, Groupe Hospitalier Pitié-Salpêtrière, Paris, France.

Brody disease is an autosomal recessive myopathy characterized by exercise-induced muscle stiffness due to mutations in the ATP2A1 gene. Almost 50 years after the initial case presentation, only 18 patients have been reported and many questions regarding the clinical phenotype and results of ancillary investigations remain unanswered, likely leading to incomplete recognition and consequently under-diagnosis. Additionally, little is known about the natural history of the disorder, genotype-phenotype correlations, and the effects of symptomatic treatment. We studied the largest cohort of Brody disease patients to date (n = 40), consisting of 22 new patients (19 novel mutations) and all 18 previously published patients. This observational study shows that the main feature of Brody disease is an exercise-induced muscle stiffness of the limbs, and often of the eyelids. Onset begins in childhood and there was no or only mild progression of symptoms over time. Four patients had episodes resembling malignant hyperthermia. The key finding at physical examination was delayed relaxation after repetitive contractions. Additionally, no atrophy was seen, muscle strength was generally preserved, and some patients had a remarkable athletic build. Symptomatic treatment was mostly ineffective or produced unacceptable side effects. EMG showed silent contractures in approximately half of the patients and no myotonia. Creatine kinase was normal or mildly elevated, and muscle biopsy showed mild myopathic changes with selective type II atrophy. Sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) activity was reduced and western blot analysis showed decreased or absent SERCA1 protein. Based on this cohort, we conclude that Brody disease should be considered in cases of exercise-induced muscle stiffness. When physical examination shows delayed relaxation, and there are no myotonic discharges at electromyography, we recommend direct sequencing of the ATP2A1 gene or next generation sequencing with a myopathy panel. Aside from clinical features, SERCA activity measurement and SERCA1 western blot can assist in proving the pathogenicity of novel ATP2A1 mutations. Finally, patients with Brody disease may be at risk for malignant hyperthermia-like episodes, and therefore appropriate perioperative measures are recommended. This study will help improve understanding and recognition of Brody disease as a distinct myopathy in the broader field of calcium-related myopathies.
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http://dx.doi.org/10.1093/brain/awz410DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7009512PMC
February 2020

Variants in NGLY1 lead to intellectual disability, myoclonus epilepsy, sensorimotor axonal polyneuropathy and mitochondrial dysfunction.

Clin Genet 2020 04 30;97(4):556-566. Epub 2020 Jan 30.

Radboud Center for Mitochondrial Medicine, Department of Pediatrics, Amalia Children's Hospital, Nijmegen, the Netherlands.

NGLY1 encodes the enzyme N-glycanase that is involved in the degradation of glycoproteins as part of the endoplasmatic reticulum-associated degradation pathway. Variants in this gene have been described to cause a multisystem disease characterized by neuromotor impairment, neuropathy, intellectual disability, and dysmorphic features. Here, we describe four patients with pathogenic variants in NGLY1. As the clinical features and laboratory results of the patients suggested a multisystem mitochondrial disease, a muscle biopsy had been performed. Biochemical analysis in muscle showed a strongly reduced ATP production rate in all patients, while individual OXPHOS enzyme activities varied from normal to reduced. No causative variants in any mitochondrial disease genes were found using mtDNA analysis and whole exome sequencing. In all four patients, variants in NGLY1 were identified, including two unreported variants (c.849T>G (p.(Cys283Trp)) and c.1067A>G (p.(Glu356Gly)). Western blot analysis of N-glycanase in muscle and fibroblasts showed a complete absence of N-glycanase. One patient showed a decreased basal and maximal oxygen consumption rates in fibroblasts. Mitochondrial morphofunction fibroblast analysis showed patient specific differences when compared to control cell lines. In conclusion, variants in NGLY1 affect mitochondrial energy metabolism which in turn might contribute to the clinical disease course.
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http://dx.doi.org/10.1111/cge.13706DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7078978PMC
April 2020

Bi-Allelic UQCRFS1 Variants Are Associated with Mitochondrial Complex III Deficiency, Cardiomyopathy, and Alopecia Totalis.

Am J Hum Genet 2020 01 26;106(1):102-111. Epub 2019 Dec 26.

Charité-Universitätsmedizin Berlin, corporate member of the Freie Universität Berlin and Humboldt-Universität zu Berlin, and Berlin Institute of Health: NeuroCure Cluster of Excellence, 10117 Berlin, Germany; Charité-Universitätsmedizin Berlin, corporate member of the Freie Universität Berlin and Humboldt-Universität zu Berlin, and Berlin Institute of Health: Department of Neuropediatrics, 13353 Berlin, Germany. Electronic address:

Isolated complex III (CIII) deficiencies are among the least frequently diagnosed mitochondrial disorders. Clinical symptoms range from isolated myopathy to severe multi-systemic disorders with early death and disability. To date, we know of pathogenic variants in genes encoding five out of 10 subunits and five out of 13 assembly factors of CIII. Here we describe rare bi-allelic variants in the gene of a catalytic subunit of CIII, UQCRFS1, which encodes the Rieske iron-sulfur protein, in two unrelated individuals. Affected children presented with low CIII activity in fibroblasts, lactic acidosis, fetal bradycardia, hypertrophic cardiomyopathy, and alopecia totalis. Studies in proband-derived fibroblasts showed a deleterious effect of the variants on UQCRFS1 protein abundance, mitochondrial import, CIII assembly, and cellular respiration. Complementation studies via lentiviral transduction and overexpression of wild-type UQCRFS1 restored mitochondrial function and rescued the cellular phenotype, confirming UQCRFS1 variants as causative for CIII deficiency. We demonstrate that mutations in UQCRFS1 can cause mitochondrial disease, and our results thereby expand the clinical and mutational spectrum of CIII deficiencies.
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http://dx.doi.org/10.1016/j.ajhg.2019.12.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7042493PMC
January 2020

KBTBD13 is an actin-binding protein that modulates muscle kinetics.

J Clin Invest 2020 02;130(2):754-767

Department of Physiology, Amsterdam University Medical Center, Netherlands.

The mechanisms that modulate the kinetics of muscle relaxation are critically important for muscle function. A prime example of the impact of impaired relaxation kinetics is nemaline myopathy caused by mutations in KBTBD13 (NEM6). In addition to weakness, NEM6 patients have slow muscle relaxation, compromising contractility and daily life activities. The role of KBTBD13 in muscle is unknown, and the pathomechanism underlying NEM6 is undetermined. A combination of transcranial magnetic stimulation-induced muscle relaxation, muscle fiber- and sarcomere-contractility assays, low-angle x-ray diffraction, and superresolution microscopy revealed that the impaired muscle-relaxation kinetics in NEM6 patients are caused by structural changes in the thin filament, a sarcomeric microstructure. Using homology modeling and binding and contractility assays with recombinant KBTBD13, Kbtbd13-knockout and Kbtbd13R408C-knockin mouse models, and a GFP-labeled Kbtbd13-transgenic zebrafish model, we discovered that KBTBD13 binds to actin - a major constituent of the thin filament - and that mutations in KBTBD13 cause structural changes impairing muscle-relaxation kinetics. We propose that this actin-based impaired relaxation is central to NEM6 pathology.
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http://dx.doi.org/10.1172/JCI124000DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6994151PMC
February 2020

Homozygous damaging SOD2 variant causes lethal neonatal dilated cardiomyopathy.

J Med Genet 2020 01 7;57(1):23-30. Epub 2019 Sep 7.

Department of Genetics, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.

Background: Idiopathic dilated cardiomyopathy (DCM) is recognised to be a heritable disorder, yet clinical genetic testing does not produce a diagnosis in >50% of paediatric patients. Identifying a genetic cause is crucial because this knowledge can affect management options, cardiac surveillance in relatives and reproductive decision-making. In this study, we sought to identify the underlying genetic defect in a patient born to consanguineous parents with rapidly progressive DCM that led to death in early infancy.

Methods And Results: Exome sequencing revealed a potentially pathogenic, homozygous missense variant, c.542G>T, p.(Gly181Val), in . This gene encodes superoxide dismutase 2 (SOD2) or manganese-superoxide dismutase, a mitochondrial matrix protein that scavenges oxygen radicals produced by oxidation-reduction and electron transport reactions occurring in mitochondria via conversion of superoxide anion (O) into HO. Measurement of hydroethidine oxidation showed a significant increase in O levels in the patient's skin fibroblasts, as compared with controls, and this was paralleled by reduced catalytic activity of SOD2 in patient fibroblasts and muscle. Lentiviral complementation experiments demonstrated that mitochondrial SOD2 activity could be completely restored on transduction with wild type SOD2.

Conclusion: Our results provide evidence that defective SOD2 may lead to toxic increases in the levels of damaging oxygen radicals in the neonatal heart, which can result in rapidly developing heart failure and death. We propose SOD2 as a novel nuclear-encoded mitochondrial protein involved in severe human neonatal cardiomyopathy, thus expanding the wide range of genetic factors involved in paediatric cardiomyopathies.
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http://dx.doi.org/10.1136/jmedgenet-2019-106330DOI Listing
January 2020

Loss of Bardet-Biedl syndrome proteins causes synaptic aberrations in principal neurons.

PLoS Biol 2019 09 3;17(9):e3000414. Epub 2019 Sep 3.

Great Ormond Street Institute of Child Health, University College London, London, United Kingdom.

Bardet-Biedl syndrome (BBS), a ciliopathy, is a rare genetic condition characterised by retinal degeneration, obesity, kidney failure, and cognitive impairment. In spite of progress made in our general understanding of BBS aetiology, the molecular and cellular mechanisms underlying cognitive impairment in BBS remain elusive. Here, we report that the loss of BBS proteins causes synaptic dysfunction in principal neurons, providing a possible explanation for the cognitive impairment phenotype observed in BBS patients. Using synaptosomal proteomics and immunocytochemistry, we demonstrate the presence of Bbs proteins in the postsynaptic density (PSD) of hippocampal neurons. Loss of Bbs results in a significant reduction of dendritic spines in principal neurons of Bbs mouse models. Furthermore, we show that spine deficiency correlates with events that destabilise spine architecture, such as impaired spine membrane receptor signalling, known to be involved in the maintenance of dendritic spines. Our findings suggest a role for BBS proteins in dendritic spine homeostasis that may be linked to the cognitive phenotype observed in BBS.
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http://dx.doi.org/10.1371/journal.pbio.3000414DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6743795PMC
September 2019

Bi-allelic GOT2 Mutations Cause a Treatable Malate-Aspartate Shuttle-Related Encephalopathy.

Am J Hum Genet 2019 09 15;105(3):534-548. Epub 2019 Aug 15.

On behalf of "United for Metabolic Diseases," 1105AZ Amsterdam, the Netherlands; Department of Laboratory Medicine, Translational Metabolic Laboratory, Radboud University Medical Centre, 6525 GA Nijmegen, the Netherlands. Electronic address:

Early-infantile encephalopathies with epilepsy are devastating conditions mandating an accurate diagnosis to guide proper management. Whole-exome sequencing was used to investigate the disease etiology in four children from independent families with intellectual disability and epilepsy, revealing bi-allelic GOT2 mutations. In-depth metabolic studies in individual 1 showed low plasma serine, hypercitrullinemia, hyperlactatemia, and hyperammonemia. The epilepsy was serine and pyridoxine responsive. Functional consequences of observed mutations were tested by measuring enzyme activity and by cell and animal models. Zebrafish and mouse models were used to validate brain developmental and functional defects and to test therapeutic strategies. GOT2 encodes the mitochondrial glutamate oxaloacetate transaminase. GOT2 enzyme activity was deficient in fibroblasts with bi-allelic mutations. GOT2, a member of the malate-aspartate shuttle, plays an essential role in the intracellular NAD(H) redox balance. De novo serine biosynthesis was impaired in fibroblasts with GOT2 mutations and GOT2-knockout HEK293 cells. Correcting the highly oxidized cytosolic NAD-redox state by pyruvate supplementation restored serine biosynthesis in GOT2-deficient cells. Knockdown of got2a in zebrafish resulted in a brain developmental defect associated with seizure-like electroencephalography spikes, which could be rescued by supplying pyridoxine in embryo water. Both pyridoxine and serine synergistically rescued embryonic developmental defects in zebrafish got2a morphants. The two treated individuals reacted favorably to their treatment. Our data provide a mechanistic basis for the biochemical abnormalities in GOT2 deficiency that may also hold for other MAS defects.
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http://dx.doi.org/10.1016/j.ajhg.2019.07.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6732527PMC
September 2019

Primary coenzyme Q10 deficiency-7: expanded phenotypic spectrum and a founder mutation in southern Chinese.

NPJ Genom Med 2019 5;4:18. Epub 2019 Aug 5.

1Department of Paediatrics & Adolescent Medicine, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong, China.

Primary coenzyme Q10 deficiency-7 (COQ10D7) is a rare mitochondrial disease caused by biallelic mutations in . Here we report the largest cohort of COQ10D7 to date, with 11 southern Chinese patients confirmed with biallelic mutations. Five of them have the classical neonatal-onset encephalo-cardiomyopathy, while the others have infantile onset with more heterogeneous clinical presentations. We also identify a founder mutation (NM_016035.5): c.370G>A, p.(Gly124Ser) for COQ10D7, suggesting a higher chance of occurrence in the southern Chinese. This study helps improve understanding of the clinical spectrum of this disorder.
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http://dx.doi.org/10.1038/s41525-019-0091-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6683205PMC
August 2019

ARX-associated infantile epileptic-dyskinetic encephalopathy with responsiveness to valproate for controlling seizures and reduced activity of muscle mitochondrial complex IV.

Brain Dev 2019 Nov 16;41(10):883-887. Epub 2019 Jul 16.

Department of Paediatrics and Adolescent Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong Special Administrative Region. Electronic address:

Background: ARX genetic defect is associated with a spectrum of neurodevelopmental disorders that exhibit a high degree of phenotypic heterogeneity.

Methods: We studied a family with a 13-year old Chinese boy and his two elder brothers presented with infantile epileptic-dyskinetic encephalopathy and clarified the unknown genetic etiology of the youngest brother by whole exome sequencing.

Results: The youngest brother of this family presented with developmental regression, dystonia, epilepsy, microcephaly, visual impairment and oromotor dysfunction. Hyperlactataemia, raised alanine and muscle complex IV deficiency indicated that he had mitochondrial dysfunction. Likely pathogenic hemizygous missense ARX variants (c.989G > A; p.Arg330His) located in conserved nuclear localization sequence was identified. The variant was carried by his asymptomatic mother and not found in his asymptomatic third elder brother. The intractable seizures showed complete but transient responsiveness to pyridoxal phosphate and finally controlled by valproate treatment.

Conclusion: This is the first case of ARX-associated encephalopathy showing mitochondrial dysfunction and transient responsiveness to pyridoxal phosphate treatment.
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http://dx.doi.org/10.1016/j.braindev.2019.07.003DOI Listing
November 2019

A fatal case of -associated primary coenzyme Q deficiency.

JIMD Rep 2019 May 3;47(1):23-29. Epub 2019 Apr 3.

Department of Paediatrics and Adolescent Medicine, Li Ka Shing Faculty of Medicine Queen Mary Hospital, The University of Hong Kong Hong Kong SAR China.

Background: Primary coenzyme Q (CoQ) deficiencies are clinically and genetically heterogeneous group of disorders associated with defects of genes involved in the CoQ biosynthesis pathway. -associated CoQ deficiency is very rare and only two cases have been reported.

Methods And Results: We report a patient with encephalo-myo-nephro-cardiopathy, persistent lactic acidosis, and basal ganglia lesions resulting in early infantile death. Using whole exome sequencing, we identified compound heterozygous variants in the gene consisting of a deletion insertion resulting in frameshift [c.599_600delinsTAATGCATC, p.(Lys200Ilefs*56)] and a missense substitution [c.319C>T, p.(Arg107Trp), NM_016138.4]. Skin fibroblast studies showed decreased combined complex II + III activity and reduction in CoQ level.

Conclusion: This third patient presenting with lethal encephalo-myo-nephro-cardiopathy represents the severe end of this ultra-rare mitochondrial disease caused by biallelic mutations. The response to CoQ supplement is poor and alternative treatment strategies should be developed for a more effective management of this disorder.
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http://dx.doi.org/10.1002/jmd2.12032DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6498831PMC
May 2019

A Mitochondrial Complex I Deficiency Phenotype Array.

Front Genet 2019 27;10:245. Epub 2019 Mar 27.

Department of Human Genetics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, Netherlands.

Mitochondrial diseases are a group of rare life-threatening diseases often caused by defects in the oxidative phosphorylation system. No effective treatment is available for these disorders. Therapeutic development is hampered by the high heterogeneity in genetic, biochemical, and clinical spectra of mitochondrial diseases and by limited preclinical resources to screen and identify effective treatment candidates. Alternative models of the pathology are essential to better understand mitochondrial diseases and to accelerate the development of new therapeutics. The fruit fly is a cost- and time-efficient model that can recapitulate a wide range of phenotypes observed in patients suffering from mitochondrial disorders. We targeted three important subunits of complex I of the mitochondrial oxidative phosphorylation system with the flexible UAS-Gal4 system and RNA interference (RNAi): NDUFS4 (ND-18), NDUFS7 (ND-20), and NDUFV1 (ND-51). Using two ubiquitous driver lines at two temperatures, we established a collection of phenotypes relevant to complex I deficiencies. Our data offer models and phenotypes with different levels of severity that can be used for future therapeutic screenings. These include qualitative phenotypes that are amenable to high-throughput drug screening and quantitative phenotypes that require more resources but are likely to have increased potential and sensitivity to show modulation by drug treatment.
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http://dx.doi.org/10.3389/fgene.2019.00245DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6445954PMC
March 2019

Panel-Based Nuclear and Mitochondrial Next-Generation Sequencing Outcomes of an Ethnically Diverse Pediatric Patient Cohort with Mitochondrial Disease.

J Mol Diagn 2019 05 11;21(3):503-513. Epub 2019 Mar 11.

Human Metabolomics, Faculty of Natural and Agricultural Sciences, North-West University, Potchefstroom, South Africa. Electronic address:

Mitochondrial disease (MD) is a group of rare inherited disorders with clinical heterogeneous phenotypes. Recent advances in next-generation sequencing (NGS) allow for rapid genetic diagnostics in patients who experience MD, resulting in significant strides in determining its etiology. This, however, has not been the case in many patient populations. We report on a molecular diagnostic study using mitochondrial DNA and targeted nuclear DNA (nDNA) NGS of an extensive cohort of predominantly sub-Saharan African pediatric patients with clinical and biochemically defined MD. Patients in this novel cohort presented mostly with muscle involvement (73%). Of the original 212 patients, a muscle respiratory chain deficiency was identified in 127 cases. Genetic analyses were conducted for these 127 cases based on biochemical deficiencies, for both mitochondrial (n = 123) and nDNA using panel-based NGS (n = 86). As a pilot investigation, whole-exome sequencing was performed in a subset of African patients (n = 8). These analyses resulted in the identification of a previously reported pathogenic mitochondrial DNA variant and seven pathogenic or likely pathogenic nDNA variants (ETFDH, SURF1, COQ6, RYR1, STAC3, ALAS2, and TRIOBP), most of which were identified via whole-exome sequencing. This study contributes to knowledge of MD etiology in an understudied, ethnically diverse population; highlights inconsistencies in genotype-phenotype correlations; and proposes future directions for diagnostic approaches in such patient populations.
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http://dx.doi.org/10.1016/j.jmoldx.2019.02.002DOI Listing
May 2019

Biallelic variants in and cause deafness and (ovario)leukodystrophy.

Neurology 2019 03 8;92(11):e1225-e1237. Epub 2019 Feb 8.

From the Departments of Child Neurology (M.S.v.d.K., M. Breur) and Neuropathology (M. Bugiani, M. Breur), and Metabolic Unit, Department of Clinical Chemistry (M.I.M., D.E.C.S., G.S.S.), Amsterdam University Medical Centers and Amsterdam Neuroscience; Department of Functional Genomics (M.S.v.d.K.), Center for Neurogenomics and Cognitive Research, VU University, Amsterdam, the Netherlands; Genetic Metabolic Disorders Research Unit (L.G.R., J. Christodoulou), The Children's Hospital at Westmead, and Discipline of Child and Adolescent Health, Sydney Medical School, University of Sydney, NSW, Australia; Architecture et Réactivité de l'ARN (J.R.-T., M.F.), UPR 9002, Université de Strasbourg, CNRS, Strasbourg, France; Institute for Molecular Bioscience (J. Crawford, C.S.), University of Queensland, St. Lucia, Queensland, Australia; Department of Neurology (J.v.G.), Radboud University Medical Center, Donders Institute for Brain, Cognition and Behaviour, Nijmegen; Department of Clinical Genetics (M.S.), Radboud University Medical Center, Nijmegen, the Netherlands; Departement Génétique Médicale (M.W.), Maladies Rares et Médecine Personnalisée, Hôpital Arnaud de Villeneuve, CHRU de Montpellier, France; Department of Clinical Genetics (Q.W.), Amsterdam University Medical Centers, the Netherlands; UF Innovation en Diagnostic Génomique des Maladies Rares (F.T.M.-T.), Centre Hospitalier Universitaire de Dijon, France; Radboud Center for Mitochondrial Medicine (R.J.R.), Translational Metabolic Laboratory, Department of Pediatrics, Radboud University Medical Center, Nijmegen, the Netherlands; Illumina Inc. (R.J.T.), San Diego, CA; AP-HP (B.K., F.M.), La Pitié-Salpêtrière University Hospital, Department of Genetics, Paris; INSERM U 1127 (B.K., C.D., F.M.), CNRS UMR 7225, Sorbonne Universités, UPMC Univ Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, Paris, France; Murdoch Children's Research Institute (J. Christodoulou, C.S.), Parkville, Victoria, Australia; Department of Paediatrics (J. Christodoulou), University of Melbourne, Australia; Institute of Human Genetics (C.D.), University Hospital Essen, University Duisburg-Essen, Germany; and Sorbonne Universités (F.M.), Neurometabolic Clinical Research Group, Paris, France.

Objective: To describe the leukodystrophy caused by pathogenic variants in and , encoding mitochondrial leucyl transfer RNA (tRNA) synthase and mitochondrial and cytoplasmic lysyl tRNA synthase, respectively.

Methods: We composed a group of 5 patients with leukodystrophy, in whom whole-genome or whole-exome sequencing revealed pathogenic variants in or . Clinical information, brain MRIs, and postmortem brain autopsy data were collected. We assessed aminoacylation activities of purified mutant recombinant mitochondrial leucyl tRNA synthase and performed aminoacylation assays on patients' lymphoblasts and fibroblasts.

Results: Patients had a combination of early-onset deafness and later-onset neurologic deterioration caused by progressive brain white matter abnormalities on MRI. Female patients with pathogenic variants had premature ovarian failure. In 2 patients, MRI showed additional signs of early-onset vascular abnormalities. In 2 other patients with and pathogenic variants, magnetic resonance spectroscopy revealed elevated white matter lactate, suggesting mitochondrial disease. Pathology in one patient with pathogenic variants displayed evidence of primary disease of oligodendrocytes and astrocytes with lack of myelin and deficient astrogliosis. Aminoacylation activities of purified recombinant mutant leucyl tRNA synthase showed a 3-fold loss of catalytic efficiency. Aminoacylation assays on patients' lymphoblasts and fibroblasts showed about 50% reduction of enzyme activity.

Conclusion: This study adds and pathogenic variants as gene defects that may underlie deafness, ovarian failure, and leukodystrophy with mitochondrial signature. We discuss the specific MRI characteristics shared by leukodystrophies caused by mitochondrial tRNA synthase defects. We propose to add aminoacylation assays as biochemical diagnostic tools for leukodystrophies.
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http://dx.doi.org/10.1212/WNL.0000000000007098DOI Listing
March 2019

Intra-patient variability of heteroplasmy levels in urinary epithelial cells in carriers of the m.3243A>G mutation.

Mol Genet Genomic Med 2019 02 4;7(2):e00523. Epub 2018 Dec 4.

Department of Pediatrics, Radboudumc Amalia Childrens Hospital, Radboud Center for Mitochondrial Medicine, Nijmegen, The Netherlands.

Background: The mitochondrial DNA m.3243A>G mutation is one the most prevalent mutation causing mitochondrial disease in adult patients. Several cohort studies have used heteroplasmy levels in urinary epithelial cells (UEC) to correlate the genotype of the patients to the clinical severity. However, the interpretation of these data is hampered by a lack of knowledge on the intra-patient variability of the heteroplasmy levels. The goal of this study was to determine the day-to-day variation of the heteroplasmy levels in UEC.

Methods: Fifteen carriers of the m.3243A>G mutation collected five urine samples in a 14-day window. Heteroplasmy levels of the m.3243A>G mutation were determined in these samples. Data from the national cohort study, including Newcastle Mitochondrial Disease Adult Scale scores and clinical diagnosis, were used.

Results: In the samples of six patients, heteroplasmy levels were within a 5% margin. In the samples collected from five patients, the margin was >20%.

Conclusion: Heteroplasmy levels of UEC in carriers of the m.3243A>G mutation have a significant day-to-day variation. The interpretation of a correlation between heteroplasmy levels in urine and disease severity is therefore not reliable. Therefore, heteroplasmy levels in UEC should not be used as a prognostic biomarker in these patients.
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http://dx.doi.org/10.1002/mgg3.523DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6393655PMC
February 2019

Diverse phenotype in patients with complex I deficiency due to mutations in NDUFB11.

Eur J Med Genet 2019 Nov 10;62(11):103572. Epub 2018 Nov 10.

Department of Clinical Genetics, United Laboratories, Tartu University Hospital, Tartu, Estonia; Department of Clinical Genetics, Institute of Clinical Medicine, University of Tartu, Tartu, Estonia. Electronic address:

Mitochondrial complex I deficiency is the most frequent mitochondrial disorder presenting in childhood and the mutational spectrum is highly heterogeneous. The NDUFB11 gene is one of the recently identified genes, which is located in the short arm of the X-chromosome. Here we report clinical, biochemical, functional and genetic findings of two male patients with lactic acidosis, hypertrophic cardiomyopathy and isolated complex I deficiency due to de novo hemizygous mutations (c.286C > T and c.328C > T) in the NDUFB11 gene. Neither of them had any skin manifestations. The NDUFB11 gene encodes a relatively small integral membrane protein NDUFB11, which is essential for the assembly of an active complex I. The expression levels of this protein was decreased in both patient cells and a lentiviral complementation experiment also supported the notion that the complex I deficiency in those two patients is caused by NDUFB11 genetic defects. Our findings together with a review of the thirteen previously described patients demonstrate a wide spectrum of clinical features associated with NDUFB11-related complex I deficiency. However, histiocytoid cardiomyopathy and/or congenital sideroblastic anemia could be indicative for mutation in the NDUFB11 gene, while the clinical manifestation of the same mutation can be highly variable.
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http://dx.doi.org/10.1016/j.ejmg.2018.11.006DOI Listing
November 2019

Pathogenic variants in glutamyl-tRNA amidotransferase subunits cause a lethal mitochondrial cardiomyopathy disorder.

Nat Commun 2018 10 3;9(1):4065. Epub 2018 Oct 3.

Section of Clinical Genetics and Metabolism, Department of Pediatrics, University of Colorado, Aurora, 80045, CO, USA.

Mitochondrial protein synthesis requires charging mt-tRNAs with their cognate amino acids by mitochondrial aminoacyl-tRNA synthetases, with the exception of glutaminyl mt-tRNA (mt-tRNA). mt-tRNA is indirectly charged by a transamidation reaction involving the GatCAB aminoacyl-tRNA amidotransferase complex. Defects involving the mitochondrial protein synthesis machinery cause a broad spectrum of disorders, with often fatal outcome. Here, we describe nine patients from five families with genetic defects in a GatCAB complex subunit, including QRSL1, GATB, and GATC, each showing a lethal metabolic cardiomyopathy syndrome. Functional studies reveal combined respiratory chain enzyme deficiencies and mitochondrial dysfunction. Aminoacylation of mt-tRNA and mitochondrial protein translation are deficient in patients' fibroblasts cultured in the absence of glutamine but restore in high glutamine. Lentiviral rescue experiments and modeling in S. cerevisiae homologs confirm pathogenicity. Our study completes a decade of investigations on mitochondrial aminoacylation disorders, starting with DARS2 and ending with the GatCAB complex.
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http://dx.doi.org/10.1038/s41467-018-06250-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6170436PMC
October 2018

Age-Dependent Decrease of Mitochondrial Complex II Activity in a Familial Mouse Model for Alzheimer's Disease.

J Alzheimers Dis 2018 ;66(1):75-82

Department of Anatomy, Radboud University Medical Center, Donders Institute for Brain Cognition and Behaviour, Nijmegen, The Netherlands.

Alzheimer's disease (AD) is a severe neurodegenerative disorder for which the exact etiology is largely unknown. An increasingly recognized and investigated notion is the pathogenic role of mitochondrial dysfunction in AD. We assessed mitochondrial oxidative-phosphorylation (OXPHOS) enzyme activities in the APPswe/PS1ΔE9 mouse model from 4.5 to 14 months of age. We show an age-dependent decrease in mitochondrial complex-II activity starting at 9 months in APP/PS1 mice. Other enzymes of the OXPHOS do not show any alterations. Since amyloid-β (Aβ) plaques are already present from 4 months of age, mitochondrial dysfunction likely occurs downstream of Aβ pathology in this mouse model.
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http://dx.doi.org/10.3233/JAD-180337DOI Listing
September 2019

Coenzyme Q10 deficiency due to a COQ4 gene defect causes childhood-onset spinocerebellar ataxia and stroke-like episodes.

Mol Genet Metab Rep 2018 Dec 13;17:19-21. Epub 2018 Sep 13.

Department of Pediatrics, Amsterdam University Medical Centers, University of Amsterdam, Amsterdam, the Netherlands.

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http://dx.doi.org/10.1016/j.ymgmr.2018.09.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6138878PMC
December 2018

Effectiveness of whole exome sequencing in unsolved patients with a clinical suspicion of a mitochondrial disorder in Estonia.

Mol Genet Metab Rep 2018 Jun 15;15:80-89. Epub 2018 Mar 15.

Department of Clinical Genetics, Institute of Clinical Medicine, University of Tartu, 2 L. Puusepa Street, Tartu 51014, Estonia.

Objective: Reaching a genetic diagnosis of mitochondrial disorders (MDs) is challenging due to their broad phenotypic and genotypic heterogeneity. However, there is growing evidence that the use of whole exome sequencing (WES) for diagnosing patients with a clinical suspicion of an MD is effective (39-60%). We aimed to study the effectiveness of WES in clinical practice in Estonia, in patients with an unsolved, but suspected MD. We also show our first results of mtDNA analysis obtained from standard WES reads.

Methods: Retrospective cases were selected from a database of 181 patients whose fibroblast cell cultures had been stored from 2003 to 2013. Prospective cases were selected during the period of 2014-2016 from patients referred to a clinical geneticist in whom an MD was suspected. We scored each patient according to the mitochondrial disease criteria (MDC) (Morava et al., 2006) after re-evaluation of their clinical data, and then performed WES analysis.

Results: A total of 28 patients were selected to the study group. A disease-causing variant was found in 16 patients (57%) using WES. An MD was diagnosed in four patients (14%), with variants in the and genes. Other variants found were associated with a neuromuscular disease ( and genes), neurodegenerative disorder (, genes), multisystemic disease ( and genes), and one in an isolated cardiomyopathy causing gene (). The mtDNA point mutation was found in the gene of one patient upon mtDNA analysis.

Conclusions: The diagnostic yield of WES in our cohort was 57%, proving to be a very good effectiveness. However, MDs were found in only 14% of the patients. We suggest WES analysis as a first-tier method in clinical genetic practice for children with any multisystem, neurological, and/or neuromuscular problem, as nuclear DNA variants are more common in children with MDs; a large number of patients harbor disease-causing variants in genes other than the mitochondria-related ones, and the clinical presentation might not always point towards an MD. We have also successfully conducted analysis of mtDNA from standard WES reads, providing further evidence that this method could be routinely used in the future.
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http://dx.doi.org/10.1016/j.ymgmr.2018.03.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6043467PMC
June 2018

Feeding difficulties, a key feature of the NDUFS4 mitochondrial disease model.

Dis Model Mech 2018 03 27;11(3). Epub 2018 Mar 27.

Khondrion BV, Philips van Leydenlaan 15, 6525 EX, Nijmegen, The Netherlands

Mitochondrial diseases are associated with a wide variety of clinical symptoms and variable degrees of severity. Patients with such diseases generally have a poor prognosis and often an early fatal disease outcome. With an incidence of 1 in 5000 live births and no curative treatments available, relevant animal models to evaluate new therapeutic regimes for mitochondrial diseases are urgently needed. By knocking down ND-18, the unique ortholog of NDUFS4, an accessory subunit of the NADH:ubiquinone oxidoreductase (Complex I), we developed and characterized several dNDUFS4 models that recapitulate key features of mitochondrial disease. Like in humans, the dNDUFS4 KD flies display severe feeding difficulties, an aspect of mitochondrial disorders that has so far been largely ignored in animal models. The impact of this finding, and an approach to overcome it, will be discussed in the context of interpreting disease model characterization and intervention studies.This article has an associated First Person interview with the first author of the paper.
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http://dx.doi.org/10.1242/dmm.032482DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5897729PMC
March 2018