Richard J Rodenburg

Radboud University Nijmegen, Nymegen, Gelderland, Netherlands

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Publications (148)681.95 Total impact

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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; · 3.46 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; · 4.07 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 10/2014; · 5.21 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; · 11.20 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; · 7.69 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; · 8.30 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.
    Annals of Clinical and Translational Neurology. 06/2014;
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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; · 3.56 Impact Factor
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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 04/2014; · 11.19 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. · 8.52 Impact Factor
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    ABSTRACT: Mutations in PLA2G6 gene have variable phenotypic outcome including infantile neuroaxonal dystrophy, atypical neuroaxonal dystrophy, idiopathic neurodegeneration with brain iron accumulation and Karak syndrome. The cause of this phenotypic variation is so far unknown which impairs both genetic diagnosis and appropriate family counseling. We report detailed clinical, electrophysiological, neuroimaging, histologic, biochemical and genetic characterization of 11 patients, from 6 consanguineous families, who were followed for a period of up to 17 years. Cerebellar atrophy was constant and the earliest feature of the disease preceding brain iron accumulation, leading to the provisional diagnosis of a recessive progressive ataxia in these patients. Ultrastructural characterization of patients' muscle biopsies revealed focal accumulation of granular and membranous material possibly resulting from defective membrane homeostasis caused by disrupted PLA2G6 function. Enzyme studies in one of these muscle biopsies provided evidence for a relatively low mitochondrial content, which is compatible with the structural mitochondrial alterations seen by electron microscopy. Genetic characterization of 11 patients led to the identification of six underlying PLA2G6 gene mutations, five of which are novel. Importantly, by combining clinical and genetic data we have observed that while the phenotype of neurodegeneration associated with PLA2G6 mutations is variable in this cohort of patients belonging to the same ethnic background, it is partially influenced by the genotype, considering the age at onset and the functional disability criteria. Molecular testing for PLA2G6 mutations is, therefore, indicated in childhood-onset ataxia syndromes, if neuroimaging shows cerebellar atrophy with or without evidence of iron accumulation.
    PLoS ONE 11/2013; 8(10):e76831. · 3.53 Impact Factor
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    ABSTRACT: Mutations of mitochondrial DNA are linked to many human diseases. Despite the identification of a large number of variants in the mitochondrially-encoded rRNA (mt-rRNA) genes, the evidence supporting their pathogenicity is, at best, circumstantial. Establishing the pathogenicity of these variations is of major diagnostic importance. Here, we aim to estimate the disruptive effect of mt-rRNA variations on the function of the mitochondrial ribosome. In the absence of direct biochemical methods to study the effect of mt-rRNA variations, we relied on the universal conservation of the rRNA fold to infer their disruptive potential. Our method, named Heterologous Inferential Analysis or HIA, combines conservational information with functional and structural data obtained from heterologous ribosomal sources. Thus, HIA's predictive power is superior to the traditional reliance on simple conservation indexes. By using HIA we have been able to evaluate the disruptive potential for a subset of uncharacterized 12S mt-rRNA variations. Our analysis revealed the existence of variations in the rRNA component of the human mitoribosome with different degrees of disruptive power. In cases where sufficient information regarding the genetic and pathological manifestation of the mitochondrial phenotype is available, HIA data can be used to predict the pathogenicity of mt-rRNA mutations. In other cases, HIA analysis will allow the prioritisation of variants for additional investigation. Eventually, HIA-inspired analysis of potentially pathogenic mt-rRNA variations, in the context of a scoring system specifically designed for these variants, could lead to a powerful diagnostic tool.
    Human Molecular Genetics 10/2013; · 7.69 Impact Factor
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    ABSTRACT: The advent of massive parallel sequencing is rapidly changing the strategies employed for the genetic diagnosis and research of rare diseases that involve a large number of genes. So far, it is not clear whether these approaches perform significantly better than conventional single gene testing as requested by clinicians. The current yield of this traditional diagnostic approach depends on a complex of factors which include gene-specific phenotype traits, and the relative frequency of involvement of specific genes. In order to gauge the impact of the paradigm shift that is occurring in molecular diagnostics, we assessed traditional Sanger based sequencing (in 2011), and exome sequencing followed by targeted bioinformatics analysis (in 2012) for 5 different conditions that are highly heterogeneous, and for which our center provides molecular diagnosis. We find that exome sequencing has a much higher diagnostic yield than Sanger sequencing for deafness, blindness, mitochondrial disease, and movement disorders. For microsatellite-stable colorectal cancer this was low under both strategies. Even if all genes that could have been ordered by physicians had been tested, the larger number of genes captured by the exome would still have led to a clearly superior diagnostic yield at a fraction of the cost. This article is protected by copyright. All rights reserved.
    Human Mutation 09/2013; · 5.21 Impact Factor
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    ABSTRACT: Leigh syndrome is a devastating neurodegenerative disease, typically manifesting in infancy or early childhood. However, also late-onset cases have been reported. Since its first description by Denis Archibald Leigh in 1951, it has evolved from a postmortem diagnosis, strictly defined by histopathological observations, to a clinical entity with indicative laboratory and radiological findings. Hallmarks of the disease are symmetrical lesions in the basal ganglia or brain stem on MRI, and a clinical course with rapid deterioration of cognitive and motor functions. Examinations of fresh muscle tissue or cultured fibroblasts are important tools to establish a biochemical and genetic diagnosis. Numerous causative mutations in mitochondrial and nuclear genes, encoding components of the oxidative phosphorylation system have been described in the past years. Moreover, dysfunctions in pyruvate dehydrogenase complex or coenzyme Q10 metabolism may be associated with Leigh syndrome. To date, there is no cure for affected patients, and treatment options are mostly unsatisfactory. Here, we review the most important clinical aspects of Leigh syndrome, and discuss diagnostic steps as well as treatment options.
    Journal of neurology, neurosurgery, and psychiatry 06/2013; · 4.87 Impact Factor
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    ABSTRACT: Background: Congenital disorders of glycosylation (CDG) form a group of inherited metabolic diseases. Although the clinical presentation shows extreme variability, the nervous system is frequently affected. Several parents of our patients diagnosed with CDG reported behavioral problems, including mood swings, depressive behavior, and anxiety. This raised the question whether patients with CDG have an increased risk for socio-emotional problems. Methods: We evaluated 18 children with confirmed CDG. The Child Behavior Checklist (CBCL) was used to screen for socio-emotional problems. To determine the disease progression and severity in CDG, the Nijmegen Paediatric CDG Rating Scale (NPCRS) was used. Results were compared to "norm scores" and to children with mitochondrial disorders and children with other chronic metabolic disorders with multisystem involvement. Results: Results showed a high prevalence of socio-emotional problems in children with CDG. Mean total scores, scores on withdrawn/depressed behavior, social problems, and somatic complaints were significantly increased. More than two thirds of our CDG patients have abnormal scores on CBCL. The mean score on social problems was significantly higher compared to our two control groups of patients with other chronic metabolic disorders. Conclusions: Patients with CDG have an increased risk of developing socio-emotional problems. A standard screening for psychological problems is recommended for the early detection of psychological problems in CDG patients.
    JIMD reports. 06/2013;
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    ABSTRACT: PURPOSE: Pheochromocytomas and paragangliomas (PGLs) are neuroendocrine tumors of sympathetic and parasympathetic paraganglia. The present study investigated the relationships between genotype-specific differences in mitochondrial function and catecholamine content in PGL tumors. EXPERIMENTAL DESIGN: Respiratory chain enzyme assays and 1H-NMR spectroscopy at 500 MHz, were performed on homogenates of 35 sporadic PGLs and 59 PGLs from patients with hereditary mutations in SDHB, SDHD, SDHAF-2, VHL, RET, NF1 and MAX. RESULTS: In SDHx related PGLs, a significant decrease in complex II activity (p<0.0001) and a significant increase in complex I, III and IV enzyme activities were observed when compared to sporadic, RET and NF1 tumors. Also, a significant increase in citrate synthase (p<0.0001) enzyme activity was observed in SDHx related PGLs when compared to sporadic, VHL, RET and NF1 related ones. An increase in succinate accumulation (p<0.001) and decrease in ATP/ADP/AMP accumulation (p<0.001) was observed when compared to sporadic PGLs and PGLs of other genotypes. Positive correlations (p<0.01) were observed between respiratory chain complex II activity and total catecholamine content and ATP/ADP/AMP and total catecholamine contents in tumor tissues. CONCLUSIONS: The present study for the first time establishes relationship between determinants of energy metabolism like activity of respiratory chain enzyme complex II, ATP/ADP/AMP content and catecholamine content in PGL tumors. Also, the present study for the first time successfully uses NMR spectroscopy to detect catecholamines in PGL tumors and provides ex vivo evidence for the accumulation of succinate in PGL tumors with a SDHx mutation.
    Clinical Cancer Research 05/2013; · 7.84 Impact Factor
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    ABSTRACT: Whole exome sequencing is a powerful tool to detect novel pathogenic mutations in patients with suspected mitochondrial disease. However, the interpretation of novel genetic variants is not always straightforward. Here, we present two siblings with a severe neonatal encephalopathy caused by complex V deficiency. The aim of this study was to uncover the underlying genetic defect using the combination of enzymatic testing and whole exome sequence analysis, and to provide evidence for causality by functional follow-up. Measurement of the oxygen consumption rate and enzyme analysis in fibroblasts were performed. Immunoblotting techniques were applied to study complex V assembly. The coding regions of the genome were analysed. Three-dimensional modelling was applied. Exome sequencing of the two siblings with complex V deficiency revealed a heterozygous mutation in the ATP5A1 gene, coding for complex V subunit α. The father carried the variant heterozygously. At the messenger RNA level, only the mutated allele was expressed in the patients, whereas the father expressed both the wild-type and the mutant allele. Gene expression data indicate that the maternal allele is not expressed, which is supported by the observation that the ATP5A1 expression levels in the patients and their mother are reduced to ∼50%. Complementation with wild-type ATP5A1 restored complex V in the patient fibroblasts, confirming pathogenicity of the defect. At the protein level, the mutation results in a disturbed interaction of the α-subunit with the β-subunit of complex V, which interferes with the stability of the complex. This study demonstrates the important value of functional studies in the diagnostic work-up of mitochondrial patients, in order to guide genetic variant prioritization, and to validate gene defects.
    Brain 04/2013; · 10.23 Impact Factor
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    ABSTRACT: It is estimated that the human mitochondrial proteome consists of 1,000-1,500 distinct proteins. The majority of these support the various biochemical pathways that are active in these organelles. Individuals with an oxidative phosphorylation disorder of unknown cause provide a unique opportunity to identify novel genes implicated in mitochondrial biology. We identified a homozygous deletion of CEP89 in a patient with isolated complex IV deficiency, intellectual disability and multisystemic problems. CEP89 is an ubiquitously expressed and highly conserved gene of unknown function. Immunocytochemistry and cellular fractionation experiments showed that CEP89 is present both in the cytosol and in the mitochondrial intermembrane space. Furthermore, we ascertained in vitro that downregulation of CEP89 resulted in a severe decrease in complex IV in-gel activity and altered mobility, suggesting that the complex is aberrantly formed. Two-dimensional BN-SDS gel analysis revealed that CEP89 associates with a high molecular weight complex. Together, these data confirm a role for CEP89 in mitochondrial metabolism. In addition, we modeled CEP89 loss of function in Drosophila. Ubiquitous knockdown of fly Cep89 decreased complex IV activity and resulted in complete lethality. Furthermore, Cep89 is required for mitochondrial integrity, membrane depolarization and synaptic transmission of photoreceptor neurons, and for (sub)synaptic organization of the larval neuromuscular junction. Finally, we tested neuronal Cep89 knockdown flies in the light-off jump reflex habituation assay, which revealed its role in learning. We conclude that CEP89 proteins play an important role in mitochondrial metabolism, especially complex IV activity, and are required for neuronal and cognitive function across evolution.
    Human Molecular Genetics 04/2013; · 7.69 Impact Factor
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    ABSTRACT: OBJECTIVE: To identify the mutated gene in a group of patients with an unclassified heritable white matter disorder sharing the same, distinct MRI pattern. METHODS: We used MRI pattern recognition analysis to select a group of patients with a similar, characteristic MRI pattern. We performed whole-exome sequencing to identify the mutated gene. We examined patients' fibroblasts for biochemical consequences of the mutant protein. RESULTS: We identified 6 patients from 5 unrelated families with a similar MRI pattern showing predominant abnormalities of the cerebellar cortex, deep cerebral white matter, and corpus callosum. The 4 tested patients had a respiratory chain complex I deficiency. Exome sequencing revealed mutations in NUBPL, encoding an iron-sulfur cluster assembly factor for complex I, in all patients. Upon identification of the mutated gene, we analyzed the MRI of a previously published case with NUBPL mutations and found exactly the same pattern. A strongly decreased amount of NUBPL protein and fully assembled complex I was found in patients' fibroblasts. Analysis of the effect of mutated NUBPL on the assembly of the peripheral arm of complex I indicated that NUBPL is involved in assembly of iron-sulfur clusters early in the complex I assembly pathway. CONCLUSION: Our data show that NUBPL mutations are associated with a unique, consistent, and recognizable MRI pattern, which facilitates fast diagnosis and obviates the need for other tests, including assessment of mitochondrial complex activities in muscle or fibroblasts.
    Neurology 04/2013; · 8.30 Impact Factor
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    ABSTRACT: Elevated urinary excretion of 3-methylglutaconic acid is considered rare in patients suspected of a metabolic disorder. In 3-methylglutaconyl-CoA hydratase deficiency (mutations in AUH), it derives from leucine degradation. In all other disorders with 3-methylglutaconic aciduria the origin is unknown, yet mitochondrial dysfunction is thought to be the common denominator. We investigate the biochemical, clinical and genetic data of 388 patients referred to our centre under suspicion of a metabolic disorder showing 3-methylglutaconic aciduria in routine metabolic screening. Furthermore, we investigate 591 patients with 50 different, genetically proven, mitochondrial disorders for the presence of 3-methylglutaconic aciduria. Three percent of all urine samples of the patients referred showed 3-methylglutaconic aciduria, often in correlation with disorders not reported earlier in association with 3-methylglutaconic aciduria (e.g. organic acidurias, urea cycle disorders, haematological and neuromuscular disorders). In the patient cohort with genetically proven mitochondrial disorders 11 % presented 3-methylglutaconic aciduria. It was more frequently seen in ATPase related disorders, with mitochondrial DNA depletion or deletion, but not in patients with single respiratory chain complex deficiencies. Besides, it was a consistent feature of patients with mutations in TAZ, SERAC1, OPA3, DNAJC19 and TMEM70 accounting for mitochondrial membrane related pathology. 3-methylglutaconic aciduria is found quite frequently in patients suspected of a metabolic disorder, and mitochondrial dysfunction is indeed a common denominator. It is only a discriminative feature of patients with mutations in AUH, TAZ, SERAC1, OPA3, DNAJC19 TMEM70. These conditions should therefore be referred to as inborn errors of metabolism with 3-methylglutaconic aciduria as discriminative feature.
    Journal of Inherited Metabolic Disease 01/2013; · 4.07 Impact Factor

Publication Stats

2k Citations
681.95 Total Impact Points


  • 2005–2014
    • Radboud University Nijmegen
      • • Department of Pediatrics
      • • Medical Centre
      Nymegen, Gelderland, Netherlands
  • 2004–2014
    • Radboud University Medical Centre (Radboudumc)
      • Department of Human Genetics
      Nymegen, Gelderland, Netherlands
  • 2013
    • St. Elisabeth Ziekenhuis Tilburg
      Tilburg, North Brabant, Netherlands
  • 2012
    • Hospital Kuala Lumpur
      Kuala Lumpor, Kuala Lumpur, Malaysia
  • 2006
    • Universität Heidelberg
      • Division of General Pediatrics
      Heidelberg, Baden-Wuerttemberg, Germany
  • 2004–2005
    • TNO
      Delft, South Holland, Netherlands