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Knerr I, Colombo R, Urquhart J, Morais A, Merinero B, Oyarzabal A, Pérez B, Jones SA, Perveen R, Preece MA, Rogers Y, Treacy EP, Mayne P, Zampino G, MacKinnon S, Wassmer E, Yue WW, Robinson I, Rodríguez-Pombo P, Olpin SE, Banka S. Expanding the genetic and phenotypic spectrum of branched-chain amino acid transferase 2 deficiency. J Inherit Metab Dis 2019; 42:809-817. [PMID: 31177572 DOI: 10.1002/jimd.12135] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Revised: 06/04/2019] [Accepted: 06/07/2019] [Indexed: 12/15/2022]
Abstract
The first step in branched-chain amino acid (BCAA) catabolism is catalyzed by the two BCAA transferase isoenzymes, cytoplasmic branched-chain amino acid transferase (BCAT) 1, and mitochondrial BCAT2. Defects in the second step of BCAA catabolism cause maple syrup urine disease (MSUD), a condition which has been far more extensively investigated. Here, we studied the consequences of BCAT2 deficiency, an ultra-rare condition in humans. We present genetic, clinical, and functional data in five individuals from four different families with homozygous or compound heterozygous BCAT2 mutations which were all detected following abnormal biochemical profile results or familial mutation segregation studies. We demonstrate that BCAT2 deficiency has a recognizable biochemical profile with raised plasma BCAAs and, in contrast with MSUD, low-normal branched-chain keto acids (BCKAs) with undetectable l-allo-isoleucine. Interestingly, unlike in MSUD, none of the individuals with BCAT2 deficiency developed acute encephalopathy even with exceptionally high BCAA levels. We observed wide-ranging clinical phenotypes in individuals with BCAT2 deficiency. While one adult was apparently asymptomatic, three individuals had presented with developmental delay and autistic features. We show that the biochemical characteristics of BCAT2 deficiency may be amenable to protein-restricted diet and that early treatment may improve outcome in affected individuals. BCAT2 deficiency is an inborn error of BCAA catabolism. At present, it is unclear whether developmental delay and autism are parts of the variable phenotypic spectrum of this condition or coincidental. Further studies will be required to explore this.
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Affiliation(s)
- Ina Knerr
- National Centre for Inherited Metabolic Disorders, Temple Street Children's University Hospital, Dublin, Ireland
| | - Roberto Colombo
- Institute of Clinical Biochemistry, Faculty of Medicine, Catholic University of the Sacred Heart, Rome, Italy
- Policlinico Agostino Gemelli, Rome, Italy
- Center for the Study of Rare Hereditary Diseases, Niguarda Ca' Granda Metropolitan Hospital, Milan, Italy
| | - Jill Urquhart
- Manchester Centre for Genomic Medicine, St Mary's Hospital, Manchester University NHS Foundation Trust, Health Innovation Manchester, Manchester, UK
| | - Ana Morais
- Centro de Diagnostico de Enfermedades Moleculares, Departamento de Biologia Molecular, Centro de Biologia Molecular Severo Ochoa, Centro de Investigacion Biomedica en Red de Enfermedades Raras, Universidad Autonoma de Madrid, Spain
| | - Begona Merinero
- Centro de Diagnostico de Enfermedades Moleculares, Departamento de Biologia Molecular, Centro de Biologia Molecular Severo Ochoa, Centro de Investigacion Biomedica en Red de Enfermedades Raras, Universidad Autonoma de Madrid, Spain
| | - Alfonso Oyarzabal
- Centro de Diagnostico de Enfermedades Moleculares, Departamento de Biologia Molecular, Centro de Biologia Molecular Severo Ochoa, Centro de Investigacion Biomedica en Red de Enfermedades Raras, Universidad Autonoma de Madrid, Spain
| | - Belén Pérez
- Centro de Diagnostico de Enfermedades Moleculares, Departamento de Biologia Molecular, Centro de Biologia Molecular Severo Ochoa, Centro de Investigacion Biomedica en Red de Enfermedades Raras, Universidad Autonoma de Madrid, Spain
| | - Simon A Jones
- Manchester Centre for Genomic Medicine, St Mary's Hospital, Manchester University NHS Foundation Trust, Health Innovation Manchester, Manchester, UK
- Division of Evolution and Genomic Sciences, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Rahat Perveen
- Division of Evolution and Genomic Sciences, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
| | - Mary A Preece
- Children's Hospital, Birmingham Women's and Children's NHS Foundation Trust, Birmingham, UK
| | - Yvonne Rogers
- National Centre for Inherited Metabolic Disorders, Temple Street Children's University Hospital, Dublin, Ireland
| | - Eileen P Treacy
- National Centre for Inherited Metabolic Disorders, Temple Street Children's University Hospital, Dublin, Ireland
- Adult Metabolic Service, Mater Misericordiae University Hospital, Dublin, Ireland
| | - Philip Mayne
- Department of Biochemistry, Temple Street Children's University Hospital, Dublin, Ireland
| | - Giuseppe Zampino
- Department of Paediatrics, Catholic University of the Sacred Heart, and Center for Rare Diseases, Policlinico Agostino Gemelli, Rome, Italy
| | - Sabrina MacKinnon
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Evangeline Wassmer
- Children's Hospital, Birmingham Women's and Children's NHS Foundation Trust, Birmingham, UK
| | - Wyatt W Yue
- Structural Genomics Consortium, Nuffield Department of Medicine, University of Oxford, Oxford, UK
| | - Ian Robinson
- Department of Radiology, Temple Street Children's University Hospital, Dublin, Ireland
| | - Pilar Rodríguez-Pombo
- Centro de Diagnostico de Enfermedades Moleculares, Departamento de Biologia Molecular, Centro de Biologia Molecular Severo Ochoa, Centro de Investigacion Biomedica en Red de Enfermedades Raras, Universidad Autonoma de Madrid, Spain
| | - Simon E Olpin
- Department of Clinical Chemistry, Sheffield Children's NHS Foundation Trust, Sheffield Children's Hospital, Sheffield, UK
| | - Siddharth Banka
- Manchester Centre for Genomic Medicine, St Mary's Hospital, Manchester University NHS Foundation Trust, Health Innovation Manchester, Manchester, UK
- Division of Evolution and Genomic Sciences, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
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Oyarzabal A, Marin-Valencia I. Synaptic energy metabolism and neuronal excitability, in sickness and health. J Inherit Metab Dis 2019; 42:220-236. [PMID: 30734319 DOI: 10.1002/jimd.12071] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/29/2018] [Revised: 01/06/2019] [Accepted: 01/30/2019] [Indexed: 12/11/2022]
Abstract
Most of the energy produced in the brain is dedicated to supporting synaptic transmission. Glucose is the main fuel, providing energy and carbon skeletons to the cells that execute and support synaptic function: neurons and astrocytes, respectively. It is unclear, however, how glucose is provided to and used by these cells under different levels of synaptic activity. It is even more unclear how diseases that impair glucose uptake and oxidation in the brain alter metabolism in neurons and astrocytes, disrupt synaptic activity, and cause neurological dysfunction, of which seizures are one of the most common clinical manifestations. Poor mechanistic understanding of diseases involving synaptic energy metabolism has prevented the expansion of therapeutic options, which, in most cases, are limited to symptomatic treatments. To shed light on the intersections between metabolism, synaptic transmission, and neuronal excitability, we briefly review current knowledge of compartmentalized metabolism in neurons and astrocytes, the biochemical pathways that fuel synaptic transmission at resting and active states, and the mechanisms by which disorders of brain glucose metabolism disrupt neuronal excitability and synaptic function and cause neurological disease in the form of epilepsy.
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Affiliation(s)
- Alfonso Oyarzabal
- Synaptic Metabolism Laboratory, Department of Neurology, Hospital Sant Joan de Deu, Barcelona, Spain
| | - Isaac Marin-Valencia
- Laboratory of Developmental Neurobiology, The Rockefeller University, New York, New York
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Ortigoza-Escobar JD, Oyarzabal A, Montero R, Artuch R, Jou C, Jiménez C, Gort L, Briones P, Muchart J, López-Gallardo E, Emperador S, Pesini ER, Montoya J, Pérez B, Rodríguez-Pombo P, Pérez-Dueñas B. Ndufs4 related Leigh syndrome: A case report and review of the literature. Mitochondrion 2016; 28:73-8. [DOI: 10.1016/j.mito.2016.04.001] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2016] [Revised: 03/31/2016] [Accepted: 04/01/2016] [Indexed: 12/30/2022]
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Oyarzabal A, Bravo-Alonso I, Sánchez-Aragó M, Rejas MT, Merinero B, García-Cazorla A, Artuch R, Ugarte M, Rodríguez-Pombo P. Mitochondrial response to the BCKDK-deficiency: Some clues to understand the positive dietary response in this form of autism. Biochim Biophys Acta Mol Basis Dis 2016; 1862:592-600. [PMID: 26809120 DOI: 10.1016/j.bbadis.2016.01.016] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Revised: 12/23/2015] [Accepted: 01/21/2016] [Indexed: 12/11/2022]
Abstract
Mutations on the mitochondrial-expressed Branched Chain α-Keto acid Dehydrogenase Kinase (BCKDK) gene have been recently associated with a novel dietary-treatable form of autism. But, being a mitochondrial metabolism disease, little is known about the impact on mitochondrial performance. Here, we analyze the mitochondrial response to the BCKDK-deficiency in patient's primary fibroblasts by measuring bioenergetics, ultra-structural and dynamic parameters. A two-fold increase in superoxide anion production, together with a reduction in ATP-linked respiration and intracellular ATP levels (down to 60%) detected in mutants fibroblasts point to a general bioenergetics depletion that could affect the mitochondrial dynamics and cell fate. Ultrastructure analysis of BCKDK-deficient fibroblasts shows an increased number of elongated mitochondria, apparently associated with changes in the mediator of inner mitochondria membrane fusion, GTPase OPA1 forms, and in the outer mitochondrial membrane, mitofusin 2/MFN2. Our data support a possible hyperfusion response of BCKDK-deficient mitochondria to stress. Cellular fate also seems to be affected as these fibroblasts show an altered proportion of the cells on G0/G1 and G2/M phases. Knockdown of BCKDK gene in control fibroblasts recapitulates most of these features. Same BCKDK-knockdown in a MSUD patient fibroblasts unmasks the direct involvement of the accelerated BCAAs catabolism in the mitochondrial dysfunction. All these data give us a clue to understand the positive dietary response to an overload of branched-chain amino acids. We hypothesize that a combination of the current therapeutic option with a protocol that considers the oxidative damage and energy expenditure, addressing the patients' individuality, might be useful for the physicians.
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Affiliation(s)
- A Oyarzabal
- Centro de Diagnóstico de Enfermedades Moleculares (CEDEM), Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), U-746 Centro de Investigación Biomédica en Red de Enfermedades Raras CIBERER-ISCIII, IDIPAZ, Universidad Autónoma de Madrid, Spain
| | - I Bravo-Alonso
- Centro de Diagnóstico de Enfermedades Moleculares (CEDEM), Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), U-746 Centro de Investigación Biomédica en Red de Enfermedades Raras CIBERER-ISCIII, IDIPAZ, Universidad Autónoma de Madrid, Spain
| | - M Sánchez-Aragó
- Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa, (CSIC-UAM), U-713 Centro de Investigación Biomédica en Red de Enfermedades Raras CIBERER-ISCIII, Instituto de Investigación Hospital 12 de Octubre, Universidad Autónoma de Madrid, Spain
| | - M T Rejas
- Servicio de Microscopía Electrónica, Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas, Universidad Autónoma de Madrid, Spain
| | - B Merinero
- Centro de Diagnóstico de Enfermedades Moleculares (CEDEM), Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), U-746 Centro de Investigación Biomédica en Red de Enfermedades Raras CIBERER-ISCIII, IDIPAZ, Universidad Autónoma de Madrid, Spain
| | - A García-Cazorla
- Department of Neurology, Hospital Sant Joan de Déu (HSJD), U-703 CIBER de Enfermedades Raras (CIBERER), Barcelona, Spain
| | - R Artuch
- Department of Biochemistry, Hospital Sant Joan de Déu (HSJD), U-703 CIBER de Enfermedades Raras (CIBERER), Barcelona, Spain
| | - M Ugarte
- Centro de Diagnóstico de Enfermedades Moleculares (CEDEM), Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), U-746 Centro de Investigación Biomédica en Red de Enfermedades Raras CIBERER-ISCIII, IDIPAZ, Universidad Autónoma de Madrid, Spain
| | - P Rodríguez-Pombo
- Centro de Diagnóstico de Enfermedades Moleculares (CEDEM), Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), U-746 Centro de Investigación Biomédica en Red de Enfermedades Raras CIBERER-ISCIII, IDIPAZ, Universidad Autónoma de Madrid, Spain.
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Ortigoza-Escobar JD, Molero-Luis M, Arias A, Oyarzabal A, Darín N, Serrano M, Garcia-Cazorla A, Tondo M, Hernández M, Garcia-Villoria J, Casado M, Gort L, Mayr JA, Rodríguez-Pombo P, Ribes A, Artuch R, Pérez-Dueñas B. Free-thiamine is a potential biomarker of thiamine transporter-2 deficiency: a treatable cause of Leigh syndrome. Brain 2015; 139:31-8. [PMID: 26657515 DOI: 10.1093/brain/awv342] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2015] [Accepted: 10/02/2015] [Indexed: 11/13/2022] Open
Abstract
Thiamine transporter-2 deficiency is caused by mutations in the SLC19A3 gene. As opposed to other causes of Leigh syndrome, early administration of thiamine and biotin has a dramatic and immediate clinical effect. New biochemical markers are needed to aid in early diagnosis and timely therapeutic intervention. Thiamine derivatives were analysed by high performance liquid chromatography in 106 whole blood and 38 cerebrospinal fluid samples from paediatric controls, 16 cerebrospinal fluid samples from patients with Leigh syndrome, six of whom harboured mutations in the SLC19A3 gene, and 49 patients with other neurological disorders. Free-thiamine was remarkably reduced in the cerebrospinal fluid of five SLC19A3 patients before treatment. In contrast, free-thiamine was slightly decreased in 15.2% of patients with other neurological conditions, and above the reference range in one SLC19A3 patient on thiamine supplementation. We also observed a severe deficiency of free-thiamine and low levels of thiamine diphosphate in fibroblasts from SLC19A3 patients. Surprisingly, pyruvate dehydrogenase activity and mitochondrial substrate oxidation rates were within the control range. Thiamine derivatives normalized after the addition of thiamine to the culture medium. In conclusion, we found a profound deficiency of free-thiamine in the CSF and fibroblasts of patients with thiamine transporter-2 deficiency. Thiamine supplementation led to clinical improvement in patients early treated and restored thiamine values in fibroblasts and cerebrospinal fluid.
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Affiliation(s)
| | - Marta Molero-Luis
- 2 Department of Clinical Biochemistry, Hospital Sant Joan de Déu, University of Barcelona, Barcelona, Spain
| | - Angela Arias
- 3 Division of Inborn Errors of Metabolism-IBC, Department of Biochemistry and Molecular Genetics, Hospital Clinic, Barcelona, Spain 4 Centre for the Biomedical Research on Rare Diseases (CIBERER), ISCIII, Spain
| | - Alfonso Oyarzabal
- 5 Department of Molecular Biology, Centro de Diagnóstico de Enfermedades Moleculares (CEDEM), Centro de Biología Molecular Severo Ochoa CSIC-UAM, IDIPAZ, Universidad Autónoma de Madrid, Madrid, Spain
| | - Niklas Darín
- 6 Department of Paediatrics, Sahlgrenska Academy, Gothenburg University, Gothenburg Sweden
| | - Mercedes Serrano
- 1 Department of Child Neurology, Hospital Sant Joan de Déu, University of Barcelona, Barcelona, Spain 4 Centre for the Biomedical Research on Rare Diseases (CIBERER), ISCIII, Spain
| | - Angels Garcia-Cazorla
- 1 Department of Child Neurology, Hospital Sant Joan de Déu, University of Barcelona, Barcelona, Spain 4 Centre for the Biomedical Research on Rare Diseases (CIBERER), ISCIII, Spain
| | - Mireia Tondo
- 2 Department of Clinical Biochemistry, Hospital Sant Joan de Déu, University of Barcelona, Barcelona, Spain
| | - María Hernández
- 2 Department of Clinical Biochemistry, Hospital Sant Joan de Déu, University of Barcelona, Barcelona, Spain
| | - Judit Garcia-Villoria
- 3 Division of Inborn Errors of Metabolism-IBC, Department of Biochemistry and Molecular Genetics, Hospital Clinic, Barcelona, Spain 4 Centre for the Biomedical Research on Rare Diseases (CIBERER), ISCIII, Spain
| | - Mercedes Casado
- 2 Department of Clinical Biochemistry, Hospital Sant Joan de Déu, University of Barcelona, Barcelona, Spain 4 Centre for the Biomedical Research on Rare Diseases (CIBERER), ISCIII, Spain
| | - Laura Gort
- 3 Division of Inborn Errors of Metabolism-IBC, Department of Biochemistry and Molecular Genetics, Hospital Clinic, Barcelona, Spain 4 Centre for the Biomedical Research on Rare Diseases (CIBERER), ISCIII, Spain
| | - Johannes A Mayr
- 7 Department of Paediatrics, Paracelsus Medical University Salzburg, Salzburg 5020, Austria
| | - Pilar Rodríguez-Pombo
- 4 Centre for the Biomedical Research on Rare Diseases (CIBERER), ISCIII, Spain 5 Department of Molecular Biology, Centro de Diagnóstico de Enfermedades Moleculares (CEDEM), Centro de Biología Molecular Severo Ochoa CSIC-UAM, IDIPAZ, Universidad Autónoma de Madrid, Madrid, Spain
| | - Antonia Ribes
- 3 Division of Inborn Errors of Metabolism-IBC, Department of Biochemistry and Molecular Genetics, Hospital Clinic, Barcelona, Spain 4 Centre for the Biomedical Research on Rare Diseases (CIBERER), ISCIII, Spain
| | - Rafael Artuch
- 2 Department of Clinical Biochemistry, Hospital Sant Joan de Déu, University of Barcelona, Barcelona, Spain 4 Centre for the Biomedical Research on Rare Diseases (CIBERER), ISCIII, Spain
| | - Belén Pérez-Dueñas
- 1 Department of Child Neurology, Hospital Sant Joan de Déu, University of Barcelona, Barcelona, Spain 4 Centre for the Biomedical Research on Rare Diseases (CIBERER), ISCIII, Spain
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Ortigoza-Escobar JD, Serrano M, Molero M, Oyarzabal A, Rebollo M, Muchart J, Artuch R, Rodríguez-Pombo P, Pérez-Dueñas B. Thiamine transporter-2 deficiency: outcome and treatment monitoring. Orphanet J Rare Dis 2014; 9:92. [PMID: 24957181 PMCID: PMC4099387 DOI: 10.1186/1750-1172-9-92] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2014] [Accepted: 06/13/2014] [Indexed: 01/14/2023] Open
Abstract
Background The clinical characteristics distinguishing treatable thiamine transporter-2 deficiency (ThTR2) due to SLC19A3 genetic defects from the other devastating causes of Leigh syndrome are sparse. Methods We report the clinical follow-up after thiamine and biotin supplementation in four children with ThTR2 deficiency presenting with Leigh and biotin-thiamine-responsive basal ganglia disease phenotypes. We established whole-blood thiamine reference values in 106 non-neurological affected children and monitored thiamine levels in SLC19A3 patients after the initiation of treatment. We compared our results with those of 69 patients with ThTR2 deficiency after a review of the literature. Results At diagnosis, the patients were aged 1 month to 17 years, and all of them showed signs of acute encephalopathy, generalized dystonia, and brain lesions affecting the dorsal striatum and medial thalami. One patient died of septicemia, while the remaining patients evidenced clinical and radiological improvements shortly after the initiation of thiamine. Upon follow-up, the patients received a combination of thiamine (10–40 mg/kg/day) and biotin (1–2 mg/kg/day) and remained stable with residual dystonia and speech difficulties. After establishing reference values for the different age groups, whole-blood thiamine quantification was a useful method for treatment monitoring. Conclusions ThTR2 deficiency is a reversible cause of acute dystonia and Leigh encephalopathy in the pediatric years. Brain lesions affecting the dorsal striatum and medial thalami may be useful in the differential diagnosis of other causes of Leigh syndrome. Further studies are needed to validate the therapeutic doses of thiamine and how to monitor them in these patients.
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Affiliation(s)
| | | | | | | | | | | | | | | | - Belén Pérez-Dueñas
- Department of Child Neurology, Sant Joan de Déu Hospital, University of Barcelona, Passeig Sant Joan de Déu, 2, Esplugues, Barcelona 08950, Spain.
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García-Cazorla A, Oyarzabal A, Fort J, Robles C, Castejón E, Ruiz-Sala P, Bodoy S, Merinero B, Lopez-Sala A, Dopazo J, Nunes V, Ugarte M, Artuch R, Palacín M, Rodríguez-Pombo P, Alcaide P, Navarrete R, Sanz P, Font-Llitjós M, Vilaseca MA, Ormaizabal A, Pristoupilova A, Agulló SB. Two novel mutations in the BCKDK (branched-chain keto-acid dehydrogenase kinase) gene are responsible for a neurobehavioral deficit in two pediatric unrelated patients. Hum Mutat 2014; 35:470-7. [PMID: 24449431 DOI: 10.1002/humu.22513] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Accepted: 01/10/2014] [Indexed: 12/22/2022]
Abstract
Inactivating mutations in the BCKDK gene, which codes for the kinase responsible for the negative regulation of the branched-chain α-keto acid dehydrogenase complex (BCKD), have recently been associated with a form of autism in three families. In this work, two novel exonic BCKDK mutations, c.520C>G/p.R174G and c.1166T>C/p.L389P, were identified at the homozygous state in two unrelated children with persistently reduced body fluid levels of branched-chain amino acids (BCAAs), developmental delay, microcephaly, and neurobehavioral abnormalities. Functional analysis of the mutations confirmed the missense character of the c.1166T>C change and showed a splicing defect r.[520c>g;521_543del]/p.R174Gfs1*, for c.520C>G due to the presence of a new donor splice site. Mutation p.L389P showed total loss of kinase activity. Moreover, patient-derived fibroblasts showed undetectable (p.R174Gfs1*) or barely detectable (p.L389P) levels of BCKDK protein and its phosphorylated substrate (phospho-E1α), resulting in increased BCKD activity and the very rapid BCAA catabolism manifested by the patients' clinical phenotype. Based on these results, a protein-rich diet plus oral BCAA supplementation was implemented in the patient homozygous for p.R174Gfs1*. This treatment normalized plasma BCAA levels and improved growth, developmental and behavioral variables. Our results demonstrate that BCKDK mutations can result in neurobehavioral deficits in humans and support the rationale for dietary intervention.
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Affiliation(s)
- Angels García-Cazorla
- Department of Neurology, Hospital Sant Joan de Déu (HSJD), CIBER de Enfermedades Raras (CIBERER), Barcelona, Spain
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Oyarzabal A, Martínez-Pardo M, Merinero B, Navarrete R, Desviat LR, Ugarte M, Rodríguez-Pombo P. A novel regulatory defect in the branched-chain α-keto acid dehydrogenase complex due to a mutation in the PPM1K gene causes a mild variant phenotype of maple syrup urine disease. Hum Mutat 2012; 34:355-62. [PMID: 23086801 DOI: 10.1002/humu.22242] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Accepted: 10/04/2012] [Indexed: 11/11/2022]
Abstract
This article describes a hitherto unreported involvement of the phosphatase PP2Cm, a recently described member of the branched-chain α-keto acid dehydrogenase (BCKDH) complex, in maple syrup urine disease (MSUD). The disease-causing mutation was identified in a patient with a mild variant phenotype, involving a gene not previously associated with MSUD. SNP array-based genotyping showed a copy-neutral homozygous pattern for chromosome 4 compatible with uniparental isodisomy. Mutation analysis of the candidate gene, PPM1K, revealed a homozygous c.417_418delTA change predicted to result in a truncated, unstable protein. No PP2Cm mutant protein was detected in immunocytochemical or Western blot expression analyses. The transient expression of wild-type PPM1K in PP2Cm-deficient fibroblasts recovered 35% of normal BCKDH activity. As PP2Cm has been described essential for cell survival, apoptosis and metabolism, the impact of its deficiency on specific metabolic stress variables was evaluated in PP2Cm-deficient fibroblasts. Increases were seen in ROS levels along with the activation of specific stress-signaling MAP kinases. Similar to that described for the pyruvate dehydrogenase complex, a defect in the regulation of BCKDH caused the aberrant metabolism of its substrate, contributing to the patient's MSUD phenotype--and perhaps others.
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Affiliation(s)
- Alfonso Oyarzabal
- Centro de Diagnóstico de Enfermedades Moleculares, Centro de Biología Molecular Severo Ochoa CSIC-UAM, Departamento de Biología Molecular, Universidad Autónoma de Madrid, CIBERER U746, IDIPAZ, Madrid, Spain
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Elvira A, Oyarzabal A, Murgiondo A, Paredes J, Juaristi G. Muerte fetal anteparto y síndrome de Sjögren oculto. Clínica e Investigación en Ginecología y Obstetricia 2010. [DOI: 10.1016/j.gine.2008.08.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Elvira A, Oyarzabal A, Lure M, Becerro A. Factores de riesgo de la muerte fetal anteparto. Clínica e Investigación en Ginecología y Obstetricia 2008. [DOI: 10.1016/s0210-573x(08)73043-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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