Richard J Rodenburg

Radboud University Nijmegen, Nymegen, Gelderland, Netherlands

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Publications (159)724.57 Total impact

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    ABSTRACT: Defects in mitochondrial translation may lead to combined respiratory chain deficiency and typically cause childhood-onset multisystem disease. Only recently, a homozygous missense mutation (c.467T > G, p.Leu156Arg) in MRPL44, encoding a protein of the large subunit of the mitochondrial ribosome, has been identified in two siblings with hypertrophic cardiomyopathy. Using exome sequencing, we identified two further unrelated patients harboring the previously reported mutation c.467T > G, p.Leu156Arg in MRPL44 in the homozygous state and compound heterozygous with a novel missense mutation c.233G > A, p.Arg78Gln, respectively. Both patients presented with childhood-onset hypertrophic cardiomyopathy, which seems to be the core clinical feature associated with MRPL44 deficiency. However, we observed several additional clinical signs and symptoms including pigmentary retinopathy, hemiplegic migraine, Leigh-like lesions on brain MRI, renal insufficiency, and hepatopathy. Our findings expand the clinical spectrum associated with MRPL44 mutations and indicate that MRPL44-associated mitochondrial dysfunction can also manifest as a progressive multisystem disease with central nervous system involvement. Of note, neurological and neuro-ophthalmological impairment seems to be a disease feature of the second and third decades of life, which should be taken into account in patient management and counseling.
    Neurogenetics 03/2015; DOI:10.1007/s10048-015-0444-2 · 2.66 Impact Factor
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    ABSTRACT: Mitochondrial disorders are characterized by a broad clinical spectrum. Identical clinical signs and symptoms can be caused by mutations in different mitochondrial or nuclear genes. Vice versa, the same mutation can lead to different phenotypes. Genetic syndromes and neuromuscular disorders mimicking mitochondrial disorders further complicate the diagnostic process. Whole exome sequencing (WES) is the state of the art next generation sequencing technique to identify genetic defects in mitochondrial disorders. Until recently it has mainly been used as a research tool. In this study, the use of WES in routine diagnostics is described. The WES data of 109 patients, referred under the suspicion of a mitochondrial disorder, were examined in two steps. First, the data were filtered using a virtual gene panel of genes known to be associated with mitochondrial disease. If negative, the entire exome was examined. A molecular diagnosis was achieved in 39 % of the heterogeneous cohort, and in 57 % of the subgroup of 42 patients with the highest suspicion for a mitochondrial disease. In addition to mutations in genes known to be associated with mitochondrial disorders (e.g. TUFM, MTFMT, FBXL4), in the subgroup of patients with the lowest suspicion for a mitochondrial disorder we found mutations in several genes associated with neuromuscular disorders (e.g. SEPN1, ACTA1) and genetic syndrome (e.g. SETBP1, ARID1B). Our results show that WES technology has been successfully implemented as a state-of-the-art, molecular diagnostic test for mitochondrial disorders as well as for the mimicking disorders in daily clinical practice. It also illustrates that clinical and biochemical phenotyping is essential for successful application of WES to diagnose individual patients.
    Journal of Inherited Metabolic Disease 03/2015; DOI:10.1007/s10545-015-9823-y · 4.14 Impact Factor
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    ABSTRACT: Novel, single nucleotide mutations were identified in the mitochondrial methionyl amino-acyl-tRNA synthetase gene (MARS2) via whole exome sequencing in two affected siblings with developmental delay, poor growth, and sensorineural hearing loss. We show that compound heterozygous mutations c.550C>T:p.Gln184* and c.424C>T:p.Arg142Trp in MARS2 lead to decreased MARS2 protein levels in patient lymphoblasts. Analysis of respiratory complex (RC) enzyme activities in patient fibroblasts revealed decreased Complex I and IV activities. Immunoblotting of patient fibroblast and lymphoblast samples revealed reduced protein levels of NDUFB8 and COXII, representing Complex I and IV respectively. Additionally, overexpression of wild-type MARS2 in patient fibroblasts increased NDUFB8 and COXII protein levels. These findings suggest that recessive single nucleotide mutations in MARS2 are causative for a new mitochondrial translation deficiency disorder with a primary phenotype including developmental delay and hypotonia. Identification of additional patients with single nucleotide mutations in MARS2 is necessary to determine if pectus carinatum is also a consistent feature of this syndrome. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Human Mutation 03/2015; DOI:10.1002/humu.22781 · 5.05 Impact Factor
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    ABSTRACT: Mitochondrial ATP production is mediated by the oxidative phosphorylation (OXPHOS) system, which consists of four multi-subunit complexes (CI-CIV) and the FoF1-ATP synthase (CV). Mitochondrial disorders including Leigh Syndrome often involve CI dysfunction, the pathophysiological consequences of which still remain incompletely understood. Here we combined experimental and computational strategies to gain mechanistic insight into the energy metabolism of isolated skeletal muscle mitochondria from 5weeks old wild-type (WT) and CI-deficient NDUFS4(-/-) (KO) mice. Enzyme activity measurements in KO mitochondria revealed a reduction of 79% in maximal CI activity (Vmax), which was paralleled by 45-72% increase in Vmax of CII, CIII, CIV and citrate synthase. Mathematical modeling of mitochondrial metabolism predicted that these Vmax changes do not affect the maximal rates of pyruvate (PYR) oxidation and ATP production in KO mitochondria. This prediction was empirically confirmed by flux measurements. In silico analysis further predicted that CI deficiency altered the concentration of intermediate metabolites, modestly increased mitochondrial NADH/NAD(+) ratio and stimulated the lower half of the TCA cycle, including CII. Several of the predicted changes were previously observed in experimental models of CI-deficiency. Interestingly, model predictions further suggested that CI deficiency only has major metabolic consequences when its activity decreases below 90% of normal levels, compatible with a biochemical threshold effect. Taken together, our results suggest that mouse skeletal muscle mitochondria possess a substantial CI overcapacity, which minimizes the effects of CI dysfunction on mitochondrial metabolism in this otherwise early fatal mouse model. Copyright © 2015. Published by Elsevier B.V.
    Biochimica et Biophysica Acta (BBA) - Bioenergetics 02/2015; DOI:10.1016/j.bbabio.2015.02.006 · 4.83 Impact Factor
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    ABSTRACT: The mitochondrial ribosomes are required for the synthesis of mitochondrial DNA-encoded subunits of the oxidative phosphorylation (OXPHOS) system. Here, we present a neonate with fatal lactic acidosis and combined OXPHOS deficiency caused by a homozygous mutation in MRPS22, a gene encoding a mitochondrial ribosomal small subunit protein. Brain imaging revealed several structural abnormalities, including agenesis of the corpus callosum, multiple periventricular cysts, and suspected intracerebral calcifications. Moreover, echocardiography demonstrated atrial and ventricular septal defects as well as a coronary artery fistula. Our report expands the clinical spectrum of this rare mitochondrial disorder and confirms the severe clinical phenotype associated with this defect.
    Neurogenetics 02/2015; DOI:10.1007/s10048-015-0440-6 · 2.66 Impact Factor
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    ABSTRACT: We studied a group of individuals with elevated urinary excretion of 3-methylglutaconic acid, neutropenia that can develop into leuke-mia, a neurological phenotype ranging from nonprogressive intellectual disability to a prenatal encephalopathy with progressive brain atrophy, movement disorder, cataracts, and early death. Exome sequencing of two unrelated individuals and subsequent Sanger sequencing of 16 individuals with an overlapping phenotype identified a total of 14 rare, predicted deleterious alleles in CLPB in 14 in-dividuals from 9 unrelated families. CLPB encodes caseinolytic peptidase B homolog ClpB, a member of the AAAþ protein family. To evaluate the relevance of CLPB in the pathogenesis of this syndrome, we developed a zebrafish model and an in vitro assay to measure ATPase activity. Suppression of clpb in zebrafish embryos induced a central nervous system phenotype that was consistent with cerebellar and cerebral atrophy that could be rescued by wild-type, but not mutant, human CLPB mRNA. Consistent with these data, the loss-of-function effect of one of the identified variants (c.1222A>G [p.Arg408Gly]) was supported further by in vitro evidence with the mutant peptides abolishing ATPase function. Additionally, we show that CLPB interacts biochemically with ATP2A2, known to be involved in apoptotic processes in severe congenital neutropenia (SCN) 3 (Kostmann disease [caused by HAX1 mutations]). Taken together, muta-tions in CLPB define a syndrome with intellectual disability, congenital neutropenia, progressive brain atrophy, movement disorder, cat-aracts, and 3-methylglutaconic aciduria.
    The American Journal of Human Genetics 02/2015; 96(2):1-13. DOI:10.1016/j.ajhg.2014.12.013 · 10.99 Impact Factor
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    ABSTRACT: In primary fibroblasts from Leigh Syndrome (LS) patients, isolated mitochondrial complex I deficiency is associated with increased reactive oxygen species levels and mitochondrial morpho-functional changes. Empirical evidence suggests these aberrations constitute linked therapeutic targets for small chemical molecules. However, the latter generally induce multiple subtle effects, meaning that in vitro potency analysis or single-parameter high-throughput cell screening are of limited use to identify these molecules. We combine automated image quantification and artificial intelligence to discriminate between primary fibroblasts of a healthy individual and a LS patient based upon their mitochondrial morpho-functional phenotype. We then evaluate the effects of newly developed Trolox variants in LS patient cells. This revealed that Trolox ornithylamide hydrochloride best counterbalanced mitochondrial morpho-functional aberrations, effectively scavenged ROS and increased the maximal activity of mitochondrial complexes I, IV and citrate synthase. Our results suggest that Trolox-derived antioxidants are promising candidates in therapy development for human mitochondrial disorders.
    Scientific Reports 01/2015; 5:8035. DOI:10.1038/srep08035 · 5.08 Impact Factor
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    ABSTRACT: COA6/C1orf31 is involved in cytochrome c oxidase (complex IV) biogenesis. We present a new pathogenic COA6 variant detected in a patient with neonatal hypertrophic cardiomyopathy and isolated complex IV deficiency. For the first time, clinical details about a COA6 deficient patient are given and patient fibroblasts are functionally characterized: COA6 protein is undetectable and steady state levels of complex IV and several of its subunits are reduced. The monomeric COX1 assembly intermediate accumulates. Using pulse-chase experiments, we demonstrate an increased turnover of mitochondrial encoded complex IV subunits. While monomeric complex IV is decreased in patient fibroblasts, the CI/CIII2/CIVn-supercomplexes remain unaffected. Copper supplementation shows a partial rescue of complex IV deficiency in patient fibroblasts. We conclude that COA6 is required for complex IV subunit stability. Furthermore, the proposed role in the copper delivery pathway to complex IV subunits is substantiated and a therapeutic lead for COA6 deficient patients is provided.This article is protected by copyright. All rights reserved
    Human Mutation 01/2015; 36(1). DOI:10.1002/humu.22715 · 5.05 Impact Factor
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    ABSTRACT: Dysfunction of complex I (CI) of the mitochondrial electron transport chain (ETC) features prominently in human pathology. Cell models of ETC dysfunction display adaptive survival responses that still are poorly understood but of relevance for therapy development. Here we comprehensively examined how primary human skin fibroblasts adapt to chronic CI inhibition. CI inhibition triggered transient and sustained changes in metabolism, redox homeostasis and mitochondrial (ultra)structure but no cell senescence/death. CI-inhibited cells consumed no oxygen and displayed minor mitochondrial depolarization, reverse-mode action of complex V, a slower proliferation rate and futile mitochondrial biogenesis. Adaptation was neither prevented by antioxidants nor associated with lower ATP or increased PGC1-α/SIRT1/mTOR levels. Survival of CI-inhibited cells was strictly glucose-dependent and accompanied by increased AMPK-α phosphorylation, which occurred without changes in ATP or cytosolic calcium levels. Conversely, cells devoid of AMPK-α died upon CI inhibition. Chronic CI inhibition did not increase mitochondrial superoxide levels or cellular lipid peroxidation and was paralleled by a specific increase in SOD2/GR, whereas SOD1/CAT/Gpx1/Gpx2/Gpx5 levels remained unchanged. Upon hormone stimulation, fully adapted cells displayed aberrant cytosolic and ER calcium handling due to hampered ATP fueling of ER calcium pumps. Using a cell model of CI inhibition we explored the temporal adaptation to CI dysfunction and circumvent problems associated with patient-derived cell systems. It is concluded that CI dysfunction triggers an adaptive program that depends on extracellular glucose and AMPK-α. This response avoids cell death by suppressing energy crisis, oxidative stress induction and substantial mitochondrial depolarization. Copyright © 2014. Published by Elsevier B.V.
    Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease 12/2014; 1852(3). DOI:10.1016/j.bbadis.2014.12.012 · 5.09 Impact Factor
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    ABSTRACT: Pyruvate oxidation defects (PODs) are among the most frequent causes of deficiencies in the mitochondrial energy metabolism and represent a substantial subset of classical mitochondrial diseases. PODs are not only caused by deficiency of subunits of the pyruvate dehydrogenase complex (PDHC) but also by various disorders recently described in the whole pyruvate oxidation route including cofactors, regulation of PDHC and the mitochondrial pyruvate carrier. Our own patients from 2000 to July 2014 and patients identified by a systematic survey of the literature from 1970 to July 2014 with a pyruvate oxidation disorder and a genetically proven defect were included in the study (n=628). Of these defects 74.2% (n=466) belong to PDHC subunits, 24.5% (n=154) to cofactors, 0.5% (n=3) to PDHC regulation and 0.8% (n=5) to mitochondrial pyruvate import. PODs are underestimated in the field of mitochondrial diseases because not all diagnostic centres include biochemical investigations of PDHC in their routine analysis. Cofactor and transport defects can be missed, if pyruvate oxidation is not measured in intact mitochondria routinely. Furthermore deficiency of the X-chromosomal PDHA1 can be biochemically missed depending on the X-inactivation pattern. This is reflected by an increasing number of patients diagnosed recently by genetic high throughput screening approaches. PDHC deficiency including regulation and import affect mainly the glucose dependent central and peripheral nervous system and skeletal muscle. PODs with combined enzyme defects affect also other organs like heart, lung and liver. The spectrum of clinical presentation of PODs is still expanding. PODs are a therapeutically interesting group of mitochondrial diseases since some can be bypassed by ketogenic diet or treated by cofactor supplementation. PDHC kinase inhibition, chaperone therapy and PGC1α stimulation is still a matter of further investigations.
    Journal of Inherited Metabolic Disease 12/2014; DOI:10.1007/s10545-014-9787-3 · 4.14 Impact Factor
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    ABSTRACT: Success rates for genomic analyses of highly heterogeneous disorders can be greatly improved if a large cohort of patient data is assembled to enhance collective capabilities for accurate sequence variant annotation, analysis, and interpretation. Indeed, molecular diagnostics requires the establishment of robust data resources to enable data sharing that informs accurate understanding of genes, variants, and phenotypes. The "Mitochondrial Disease Sequence Data Resource (MSeqDR) Consortium" is a grass-roots effort facilitated by the United Mitochondrial Disease Foundation to identify and prioritize specific genomic data analysis needs of the global mitochondrial disease clinical and research community. A central Web portal (https://mseqdr.org) facilitates the coherent compilation, organization, annotation, and analysis of sequence data from both nuclear and mitochondrial genomes of individuals and families with suspected mitochondrial disease. This Web portal provides users with a flexible and expandable suite of resources to enable variant-, gene-, and exome-level sequence analysis in a secure, Web-based, and user-friendly fashion. Users can also elect to share data with other MSeqDR Consortium members, or even the general public, either by custom annotation tracks or through the use of a convenient distributed annotation system (DAS) mechanism. A range of data visualization and analysis tools are provided to facilitate user interrogation and understanding of genomic, and ultimately phenotypic, data of relevance to mitochondrial biology and disease. Currently available tools for nuclear and mitochondrial gene analyses include an MSeqDR GBrowse instance that hosts optimized mitochondrial disease and mitochondrial DNA (mtDNA) specific annotation tracks, as well as an MSeqDR locus-specific database (LSDB) that curates variant data on more than 1300 genes that have been implicated in mitochondrial disease and/or encode mitochondria-localized proteins. MSeqDR is integrated with a diverse array of mtDNA data analysis tools that are both freestanding and incorporated into an online exome-level dataset curation and analysis resource (GEM.app) that is being optimized to support needs of the MSeqDR community. In addition, MSeqDR supports mitochondrial disease phenotyping and ontology tools, and provides variant pathogenicity assessment features that enable community review, feedback, and integration with the public ClinVar variant annotation resource. A centralized Web-based informed consent process is being developed, with implementation of a Global Unique Identifier (GUID) system to integrate data deposited on a given individual from different sources. Community-based data deposition into MSeqDR has already begun. Future efforts will enhance capabilities to incorporate phenotypic data that enhance genomic data analyses. MSeqDR will fill the existing void in bioinformatics tools and centralized knowledge that are necessary to enable efficient nuclear and mtDNA genomic data interpretation by a range of shareholders across both clinical diagnostic and research settings. Ultimately, MSeqDR is focused on empowering the global mitochondrial disease community to better define and explore mitochondrial diseases. Copyright © 2014 Elsevier Inc. All rights reserved.
    Molecular Genetics and Metabolism 12/2014; DOI:10.1016/j.ymgme.2014.11.016 · 2.83 Impact Factor
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    ABSTRACT: Here we present a Dutch family with a novel disease-causing mutation in the mitochondrial tRNASer(UCN) gene, m.7507A>G. The index patient died during the neonatal period due to cardio- respiratory failure and fatal lactic acidosis. A second patient, his cousin, has severe hearing loss necessitating cochlear implants and progressive exercise intolerance. Laboratory investigations of both patients revealed combined deficiencies of the enzyme complexes of the mitochondrial respiratory chain in several tissues. Reduced levels of fully assembled complexes I and IV in fibroblasts by BN-PAGE associated with (near) homoplasmic levels of the m.7507A>G mutation in several tissues and a severe reduction in the steady-state level of mt-tRNASer(UCN) in fibroblasts were observed. The novel mitochondrial DNA mutation was shown to segregate with disease; several healthy maternal family members showed high heteroplasmy levels (up to 76 +/- 4 % in blood and 68 +/-4 % in fibroblasts) which did not lead to any alterations in the activities of the enzyme complexes of the respiratory chain in fibroblasts or clinical signs and symptoms. We hereby conclude that the m.7507A>G mutation causes a heterogeneous clinical phenotype and is only pathogenic at very high levels of mtDNA heteroplasmy.
    Neuromuscular Disorders 11/2014; 25(3). DOI:10.1016/j.nmd.2014.11.002 · 3.13 Impact Factor
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    ABSTRACT: Despite major advances in understanding the pathophysiology of mitochondrial diseases, clinical management of these conditions remains largely supportive, and no effective treatment is available. We therefore assumed that the burden of disease combined with the lack of adequate treatment leaves open a big market for complementary and alternative medicine use. The objective of this study was to evaluate the use and perceived effectiveness of complementary and alternative medicine in children and adults with genetically proven mitochondrial disease. The reported use was surprisingly high, with 88 % of children and 91 % of adults having used some kind of complementary and alternative medicine in the last 2 years. Also, the mean cost of these treatments was impressive, being 489/year for children and 359/year for adult patients. Over-the-counter remedies (e.g., food supplements, homeopathy) and self-help techniques (e.g., Reiki, yoga) were the most frequently used complementary and alternative therapies in our cohort: 54 % of children and 60 % of adults reported the various complementary and alternative medicine therapies to be effective. Given the fact that currently no effective treatment exists, further research toward the different therapies is needed, as our study clearly demonstrates that such therapies are highly sought after by affected patients.
    Journal of Inherited Metabolic Disease 10/2014; DOI:10.1007/s10545-014-9773-9 · 4.14 Impact Factor
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    ABSTRACT: Cytochrome c oxidase (COX) deficiency is a frequent biochemical abnormality in mitochondrial disorders, but a large fraction of cases remains genetically undetermined. Whole-exome sequencing led to the identification of APOPT1 mutations in two Italian sisters and in a third Turkish individual presenting severe COX deficiency. All three subjects presented a distinctive brain MRI pattern characterized by cavitating leukodystrophy, predominantly in the posterior region of the cerebral hemispheres. We then found APOPT1 mutations in three additional unrelated children, selected on the basis of these particular MRI features. All identified mutations predicted the synthesis of severely damaged protein variants. The clinical features of the six subjects varied widely from acute neurometabolic decompensation in late infancy to subtle neurological signs, which appeared in adolescence; all presented a chronic, long-surviving clinical course. We showed that APOPT1 is targeted to and localized within mitochondria by an N-terminal mitochondrial targeting sequence that is eventually cleaved off from the mature protein. We then showed that APOPT1 is virtually absent in fibroblasts cultured in standard conditions, but its levels increase by inhibiting the proteasome or after oxidative challenge. Mutant fibroblasts showed reduced amount of COX holocomplex and higher levels of reactive oxygen species, which both shifted toward control values by expressing a recombinant, wild-type APOPT1 cDNA. The shRNA-mediated knockdown of APOPT1 in myoblasts and fibroblasts caused dramatic decrease in cell viability. APOPT1 mutations are responsible for infantile or childhood-onset mitochondrial disease, hallmarked by the combination of profound COX deficiency with a distinctive neuroimaging presentation.
    The American Journal of Human Genetics 08/2014; 95(3). DOI:10.1016/j.ajhg.2014.08.003 · 10.99 Impact Factor
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    ABSTRACT: Complex III (cytochrome bc1) is a protein complex of the mitochondrial inner membrane that transfers electrons from ubiquinol to cytochrome c. Its assembly requires the coordinated expression of mitochondrial encoded cytochrome b and nuclear encoded subunits and assembly factors. Complex III deficiency is a severe multisystem disorder caused by mutations in subunit genes or assembly factors. Sequence-profile-based orthology predicts C11orf83, hereafter named UQCC3, to be the ortholog of the fungal complex III assembly factor CBP4. We describe a homozygous c.59T>A missense mutation in UQCC3 from a consanguineous patient diagnosed with isolated complex III deficiency, displaying lactic acidosis, hypoglycemia, hypotonia and delayed development without dysmorphic features. Patient fibroblasts have reduced complex III activity and lower levels of the holocomplex and its subunits than controls. They have no detectable UQCC3 protein and have lower levels of cytochrome b protein. Furthermore, in patient cells cytochrome b is absent from a high molecular weight complex III. UQCC3 is reduced in cells depleted for the complex III assembly factors UQCC1 and UQCC2. Conversely, absence of UQCC3 in patient cells does not affect UQCC1 and UQCC2. This suggests that UQCC3 functions in the complex III assembly pathway downstream of UQCC1 and UQCC2 and is consistent with what is known about the function of Cbp4 and of the fungal orthologs of UQCC1 and UQCC2, Cbp3 and Cbp6. We conclude that UQCC3 functions in complex III assembly and that the c.59T>A mutation has a causal role in complex III deficiency.
    Human Molecular Genetics 07/2014; 23(23). DOI:10.1093/hmg/ddu357 · 6.68 Impact Factor
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    ABSTRACT: Objective Deficiency of pyruvate dehydrogenase complex (PDHC) is the most common genetic disorder leading to lactic acidosis. PDHC deficiency is genetically heterogenous and most patients have defects in the X-linked E1-α gene but defects in the other components of the complex encoded by PDHB, PDHX, DLAT, DLD genes or in the regulatory enzyme encoded by PDP1 have also been found. Phenylbutyrate enhances PDHC enzymatic activity in vitro and in vivo by increasing the proportion of unphosphorylated enzyme through inhibition of pyruvate dehydrogenase kinases and thus, has potential for therapy of patients with PDHC deficiency. In the present study, we investigated response to phenylbutyrate of multiple cell lines harboring all known gene defects resulting in PDHC deficiency.Methods Fibroblasts of patients with PDHC deficiency were studied for their enzyme activity at baseline and following phenylbutyrate incubation. Drug responses were correlated with genotypes and protein levels by Western blotting.ResultsLarge deletions affecting PDHA1 that result in lack of detectable protein were unresponsive to phenylbutyrate, whereas increased PDHC activity was detected in most fibroblasts harboring PDHA1 missense mutations. Mutations affecting the R349-α residue were directed to proteasome degradation and were consistently unresponsive to short-time drug incubation but longer incubation resulted in increased levels of enzyme activity and protein that may be due to an additional effect of phenylbutyrate as a molecular chaperone.InterpretationPDHC enzyme activity was enhanced by phenylbutyrate in cells harboring missense mutations in PDHB, PDHX, DLAT, DLD, and PDP1 genes. In the prospect of a clinical trial, the results of this study may allow prediction of in vivo response in patients with PDHC deficiency harboring a wide spectrum of molecular defects.
    07/2014; 1(7). DOI:10.1002/acn3.73
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    ABSTRACT: Hypomyelinating disorders of the central nervous system are still a diagnostic challenge as many patients remain without genetic diagnosis. Using MRI pattern recognition and whole exome sequencing, we could ascertain compound heterozygous mutations in RARS in four patients with hypomyelination. Clinical features included severe spasticity and nystagmus. RARS encodes the cytoplasmic arginyl-tRNA synthetase, an enzyme essential for RNA translation. This protein is one of the subunits of the multisynthetase complex, which emerges as a key player in myelination. ANN NEUROL 2014. © 2014 American Neurological Association.
    Annals of Neurology 07/2014; 76(1). DOI:10.1002/ana.24167 · 11.91 Impact Factor
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    ABSTRACT: To determine the value of fibroblast growth factor 21 (FGF21), a recently discovered biomarker for mitochondrial disease, in predicting clinical disease severity and disease progression in adult carriers of the m.3243A>G mutation.METHODS: In the context of a national inventory, the heteroplasmy levels of the m.3243A>G mutation were measured in leukocytes and urinary epithelial cells. The Newcastle Mitochondrial Disease Adult Scale score was determined and blood was drawn for measuring FGF21 concentration. Twenty-five of the included initial patients studied were then selected randomly for a follow-up study.RESULTS: This prognostic study included 99 adult carriers of the m.3243A>G mutation. Our analysis revealed a moderate, significant correlation between FGF21 concentration and disease severity (r = 0.49; p = <0.001). No significant correlations were found between disease severity and the heteroplasmy percentage determined in urinary epithelial cells or the heteroplasmy percentage determined in leukocytes. Weak but significant correlations were also found between FGF21 concentration and the severity of the myopathy (r = 0.38; p = <0.001) and between the concentration of FGF21 and the severity of the encephalopathy (r = 0.30; p = <0.001). Repeated measurements following 25 subjects for 2 years revealed no significant correlation between FGF21 concentration and disease progression.CONCLUSIONS: Measuring FGF21 concentration had little added value in monitoring and predicting the disease course in this specific patient group.
    Neurology 06/2014; DOI:10.1212/WNL.0000000000000578 · 8.30 Impact Factor
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    ABSTRACT: Defects in complex II of the mitochondrial respiratory chain are a rare cause of mitochondrial disorders. Underlying autosomal-recessive genetic defects are found in most of the 'SDHx' genes encoding complex II (SDHA, SDHB, SDHC, and SDHD) and its assembly factors. Interestingly, SDHx genes also function as tumor suppressor genes in hereditary paragangliomas, pheochromocytomas, and gastrointestinal stromal tumors. In these cases, the affected patients are carrier of a heterozygeous SDHx germline mutation. Until now, mutations in SDHx associated with mitochondrial disease have not been reported in association with hereditary tumors and vice versa. Here, we characterize four patients with isolated complex II deficiency caused by mutations in SDHA presenting with multisystem mitochondrial disease including Leigh syndrome (LS) and/or leukodystrophy. Molecular genetic analysis revealed three novel mutations in SDHA. Two mutations (c.64-2A>G and c.1065-3C>A) affect mRNA splicing and result in loss of protein expression. These are the first mutations described affecting SDHA splicing. For the third new mutation, c.565T>G, we show that it severely affects enzyme activity. Its pathogenicity was confirmed by lentiviral complementation experiments on the fibroblasts of patients carrying this mutation. It is of special interest that one of our LS patients harbored the c.91C>T (p.Arg31*) mutation that was previously only reported in association with paragangliomas and pheochromocytomas, tightening the gap between these two rare disorders. As tumor screening is recommended for SDHx mutation carriers, this should also be considered for patients with mitochondrial disorders and their family members.European Journal of Human Genetics advance online publication, 30 April 2014; doi:10.1038/ejhg.2014.80.
    European journal of human genetics: EJHG 04/2014; 23(2). DOI:10.1038/ejhg.2014.80 · 4.23 Impact Factor
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    ABSTRACT: Mitochondrial oxidative phosphorylation (OXPHOS) is responsible for generating the majority of cellular ATP. Complex III (ubiquinol-cytochrome c oxidoreductase) is the third of five OXPHOS complexes. Complex III assembly relies on the coordinated expression of the mitochondrial and nuclear genomes, with 10 subunits encoded by nuclear DNA and one by mitochondrial DNA (mtDNA). Complex III deficiency is a debilitating and often fatal disorder that can arise from mutations in complex III subunit genes or one of three known complex III assembly factors. The molecular cause for complex III deficiency in about half of cases, however, is unknown and there are likely many complex III assembly factors yet to be identified. Here, we used Massively Parallel Sequencing to identify a homozygous splicing mutation in the gene encoding Ubiquinol-Cytochrome c Reductase Complex Assembly Factor 2 (UQCC2) in a consanguineous Lebanese patient displaying complex III deficiency, severe intrauterine growth retardation, neonatal lactic acidosis and renal tubular dysfunction. We prove causality of the mutation via lentiviral correction studies in patient fibroblasts. Sequence-profile based orthology prediction shows UQCC2 is an ortholog of the Saccharomyces cerevisiae complex III assembly factor, Cbp6p, although its sequence has diverged substantially. Co-purification studies show that UQCC2 interacts with UQCC1, the predicted ortholog of the Cbp6p binding partner, Cbp3p. Fibroblasts from the patient with UQCC2 mutations have deficiency of UQCC1, while UQCC1-depleted cells have reduced levels of UQCC2 and complex III. We show that UQCC1 binds the newly synthesized mtDNA-encoded cytochrome b subunit of complex III and that UQCC2 patient fibroblasts have specific defects in the synthesis or stability of cytochrome b. This work reveals a new cause for complex III deficiency that can assist future patient diagnosis, and provides insight into human complex III assembly by establishing that UQCC1 and UQCC2 are complex III assembly factors participating in cytochrome b biogenesis.
    PLoS Genetics 12/2013; 9(12):e1004034. DOI:10.1371/journal.pgen.1004034 · 8.17 Impact Factor

Publication Stats

3k Citations
724.57 Total Impact Points

Institutions

  • 2005–2015
    • Radboud University Nijmegen
      • • Department of Laboratory Medicine
      • • Medical Centre
      Nymegen, Gelderland, Netherlands
    • Leiden University
      Leyden, South Holland, Netherlands
  • 2004–2015
    • Radboud University Medical Centre (Radboudumc)
      • Department of Human Genetics
      Nymegen, Gelderland, Netherlands
  • 2012
    • Hospital Kuala Lumpur
      Kuala Lumpor, Kuala Lumpur, Malaysia