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G.P.3.07 Novel mutation in SUCLA2 gene: Encephalomyopathy, dystonia and deafness associated with mild methylmalonic aciduria and mtDNA depletions
Abstracts / Neuromuscular Disorders 19 (2009) 543–660
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to our service at age 9 years with myopathy, chronic renal failure, learning difficulties and persistent lactic acidosis. Muscle biopsy revealed evidence of cytochrome c oxidase (COX)-positive, ragged red fibres which were associated with an isolated biochemical defect involving respiratory chain complex I. Sequencing of mtDNA from muscle revealed a novel, heteroplasmic single base deletion in the mitochondrially-encoded NADH dehydrogenase subunit 5 (MTND5) gene. The m.12425delA frameshift mutation is the first frameshift mutation to be reported within any of the MT-ND genes and predicts the premature truncation of the ND5 protein, from 604 amino acids encoded by wild type sequences, to a polypeptide of just 35 amino acids. Heteroplasmy levels in multiple tissue types were quantified using the Applied Biosystems SNaPshotÒ minisequencing assay. The results of the SNaPshotÒ assay confirmed the presence of the m.12425delA mutation at high levels in the patient’s skeletal muscle and also detected the mutation in blood, urine and buccal at lower levels of mtDNA heteroplasmy. The m.12425delA mutation was absent in all maternal tissues available for genetic testing (blood, urine and buccal cells) suggesting the mutation had arisen de novo in the proband. Our report expands the spectrum of mtDNA mutation associated with paediatric complex I deficiency, confirms mtDNA defects as an important cause of this biochemical abnormality and validates the SNaPshotÒ technology as a rapid and reliable tool for the accurate quantification of heteroplasmic mtDNA mutations.
regated with the COX defect in individual fibres showing a remarkable skewing of mutation load between COX-positive (mean mutant load 1.4%) and COX-deficient (mean mutant load 96%). We speculate whether the nuclear genetic defects influence the behaviour and expression of this mtDNA mutation, and further highlight a problem with identifying pathogenic mtDNA mutations which may go undetected by established screening methodologies.
doi:10.1016/j.nmd.2009.06.063
Introduction: SUCLA2 gene encodes the B subunit of the Krebs cycle enzyme succinyl-CoA ligasa that catalyses the formation of succinate and ATP from succinyl-CoA and ADP. Recently mutations in this gene have been associated with severe and early encephalopathy with mild methylmalonic aciduria and mtDNA depletion. Hereby we report on a child affected by severe encephalomyopathy, dyskinesias and neurosensorial deafness caused by a novel mutation in SUCLA2 gene. Case report: A 14 month old girl is the second child of nonconsanguineous healthy parents from different ethnic origin (Japanese father and Peruan mother). Delayed motor milestones and failure to thrive were noticed from the age of 4 months. At that time the main clinical symptom was severe hypotonia, lack of head and trunk control and dyskinesias. Currently no motor development improvement has been observed except for a better environment interaction. Biochemical studies showed hyperlactacidemia, mild methylmalonic aciduria and plasma carnitine ester profiling increased. Muscle biopsy showed a well preserved pattern with COX stain reduction and mild lipids increased in some scattered fibres. Brainstem auditory evoked potentials showed neurosensorial deafness. Brain MRI reveals mild cerebral atrophy. Cardiac, fundoscopy, visual evoked potentials, renal and hepatic function were normal. Real time polymerase chain reaction in muscle showed 78% depletions in mtDNA. Mutation analysis of the SUCLA2 gene on genomic DNA showed a novel compound heterozygous mutation (p.G350S/ p.G350V). Comments: 1. Early severe encephalopathy with dyskinesias should prompt the clinicians to search for laboratory clue, mild methylmalonic aciduria, hyperlactacidemia and abnormal profiling carnitine esters in order to rule out this new entity. 2. The different ethnic origin of the parents suggests that SUCLA2 gene mutation may have a wide geographic distribution.
G.P.3.06 Neuromuscular disease presentation with three genetic defects involving two genomes: The characterisation of a novel mitochondrial tRNA mutation exhibiting skewed segregation M. Al-Dosary 1, R. Whittaker 1, J. Hood 2, R. McFarland 1, J.A. Goodship 3, D.M. Turnbull 1, R.W. Taylor1 1 Newcastle University, Mitochondrial Research Group, Newcastle upon Tyne, United Kingdom, 2 Newcastle General Hospital, Regional Neurosciences Centre, Newcastle upon Tyne, United Kingdom, 3 Newcastle University, Institute of Human Genetics, Newcastle upon Tyne, United Kingdom
An extensive range of molecular defects have been identified in the human mitochondrial genome (mtDNA), many associated with well-characterised, progressive neurological syndromes. Mutation of nuclear genes involved in mtDNA maintenance can lead to secondary mtDNA abnormalities including multiple mtDNA deletions and mtDNA depletion. Point mutations within mitochondrial tRNA genes are arguably the commonest mtDNA defect observed, and are typically present at high levels in affected tissues and associated with a mosaic pattern of cytochrome c oxidase (COX) deficiency. We describe a patient who presented in his 30s to a mitochondrial clinic with progressive bilateral ptosis, PEO and increasing difficulty with walking. He had previously been diagnosed in childhood with a dominant, demyelinating polyneuropathy, confirmed as HMSN type 1A due to PMP22 gene duplication. He had also developed gout, presenting in acute renal failure with a grossly elevated plasma urate due to an X-linked recessive c.481G>T (p.A161S) HPRT gene mutation. He underwent muscle biopsy on suspicion of an underlying mitochondrial genetic defect, which revealed 15% COXdeficient fibres. Screens for mtDNA rearrangements and mtDNA depletion were negative, as was mtDNA genome sequencing of homogenate muscle DNA. Sequencing of individual, laser-captured COX-deficient fibres did however identify a novel tRNA mutation at high levels in all affected cells. The tRNA mutation was found to be present at surprisingly low levels (18%) in mature muscle, yet seg-
doi:10.1016/j.nmd.2009.06.064
G.P.3.07 Novel mutation in SUCLA2 gene: Encephalomyopathy, dystonia and deafness associated with mild methylmalonic aciduria and mtDNA depletions A.E.N. Nascimento Osorio1, A.N.S. Navarro-Sastre 2, J.C. Colomer 3, C.P. Paredes 3, A.G. Gutierrez 3, C.O. Ortez 3, M.V. Vilaseca 4, J.M. Montoya 5, T.R. Ribes 2 1 Hospital Sant Joan de Deu, Servei de Neurologia, Unitat de Patologia nuromuscular, Barcelona, Spain, 2 Instituto de Bioquimica Clinica y Genetica Molecular, Barcelona, Spain, 3 Hospital Sant Joan de Deu, Unitat de Patologia Neuromuscular, S. Neurologia, Barcelona, Spain, 4 Hospital Sant Joan de Deu, Bioquimica, Barcelona, Spain, 5 Universidad de Zaragoza, Zaragoza, Spain
doi:10.1016/j.nmd.2009.06.065
G.P.3.08 Myoclonic epilepsy, cortical dysplasia and mitochondrial complex I deficiency: A case report C. Nesti1, M. Mancuso 1, L. Petrozzi 1, F.M. Santorelli 2, A. Rocchi 1, G. Ali 3, A. Tessa 2, A. LoGerfo 1, A. Iudice 1, G. Siciliano 1
563
to our service at age 9 years with myopathy, chronic renal failure, learning difficulties and persistent lactic acidosis. Muscle biopsy revealed evidence of cytochrome c oxidase (COX)-positive, ragged red fibres which were associated with an isolated biochemical defect involving respiratory chain complex I. Sequencing of mtDNA from muscle revealed a novel, heteroplasmic single base deletion in the mitochondrially-encoded NADH dehydrogenase subunit 5 (MTND5) gene. The m.12425delA frameshift mutation is the first frameshift mutation to be reported within any of the MT-ND genes and predicts the premature truncation of the ND5 protein, from 604 amino acids encoded by wild type sequences, to a polypeptide of just 35 amino acids. Heteroplasmy levels in multiple tissue types were quantified using the Applied Biosystems SNaPshotÒ minisequencing assay. The results of the SNaPshotÒ assay confirmed the presence of the m.12425delA mutation at high levels in the patient’s skeletal muscle and also detected the mutation in blood, urine and buccal at lower levels of mtDNA heteroplasmy. The m.12425delA mutation was absent in all maternal tissues available for genetic testing (blood, urine and buccal cells) suggesting the mutation had arisen de novo in the proband. Our report expands the spectrum of mtDNA mutation associated with paediatric complex I deficiency, confirms mtDNA defects as an important cause of this biochemical abnormality and validates the SNaPshotÒ technology as a rapid and reliable tool for the accurate quantification of heteroplasmic mtDNA mutations.
regated with the COX defect in individual fibres showing a remarkable skewing of mutation load between COX-positive (mean mutant load 1.4%) and COX-deficient (mean mutant load 96%). We speculate whether the nuclear genetic defects influence the behaviour and expression of this mtDNA mutation, and further highlight a problem with identifying pathogenic mtDNA mutations which may go undetected by established screening methodologies.
doi:10.1016/j.nmd.2009.06.063
Introduction: SUCLA2 gene encodes the B subunit of the Krebs cycle enzyme succinyl-CoA ligasa that catalyses the formation of succinate and ATP from succinyl-CoA and ADP. Recently mutations in this gene have been associated with severe and early encephalopathy with mild methylmalonic aciduria and mtDNA depletion. Hereby we report on a child affected by severe encephalomyopathy, dyskinesias and neurosensorial deafness caused by a novel mutation in SUCLA2 gene. Case report: A 14 month old girl is the second child of nonconsanguineous healthy parents from different ethnic origin (Japanese father and Peruan mother). Delayed motor milestones and failure to thrive were noticed from the age of 4 months. At that time the main clinical symptom was severe hypotonia, lack of head and trunk control and dyskinesias. Currently no motor development improvement has been observed except for a better environment interaction. Biochemical studies showed hyperlactacidemia, mild methylmalonic aciduria and plasma carnitine ester profiling increased. Muscle biopsy showed a well preserved pattern with COX stain reduction and mild lipids increased in some scattered fibres. Brainstem auditory evoked potentials showed neurosensorial deafness. Brain MRI reveals mild cerebral atrophy. Cardiac, fundoscopy, visual evoked potentials, renal and hepatic function were normal. Real time polymerase chain reaction in muscle showed 78% depletions in mtDNA. Mutation analysis of the SUCLA2 gene on genomic DNA showed a novel compound heterozygous mutation (p.G350S/ p.G350V). Comments: 1. Early severe encephalopathy with dyskinesias should prompt the clinicians to search for laboratory clue, mild methylmalonic aciduria, hyperlactacidemia and abnormal profiling carnitine esters in order to rule out this new entity. 2. The different ethnic origin of the parents suggests that SUCLA2 gene mutation may have a wide geographic distribution.
G.P.3.06 Neuromuscular disease presentation with three genetic defects involving two genomes: The characterisation of a novel mitochondrial tRNA mutation exhibiting skewed segregation M. Al-Dosary 1, R. Whittaker 1, J. Hood 2, R. McFarland 1, J.A. Goodship 3, D.M. Turnbull 1, R.W. Taylor1 1 Newcastle University, Mitochondrial Research Group, Newcastle upon Tyne, United Kingdom, 2 Newcastle General Hospital, Regional Neurosciences Centre, Newcastle upon Tyne, United Kingdom, 3 Newcastle University, Institute of Human Genetics, Newcastle upon Tyne, United Kingdom
An extensive range of molecular defects have been identified in the human mitochondrial genome (mtDNA), many associated with well-characterised, progressive neurological syndromes. Mutation of nuclear genes involved in mtDNA maintenance can lead to secondary mtDNA abnormalities including multiple mtDNA deletions and mtDNA depletion. Point mutations within mitochondrial tRNA genes are arguably the commonest mtDNA defect observed, and are typically present at high levels in affected tissues and associated with a mosaic pattern of cytochrome c oxidase (COX) deficiency. We describe a patient who presented in his 30s to a mitochondrial clinic with progressive bilateral ptosis, PEO and increasing difficulty with walking. He had previously been diagnosed in childhood with a dominant, demyelinating polyneuropathy, confirmed as HMSN type 1A due to PMP22 gene duplication. He had also developed gout, presenting in acute renal failure with a grossly elevated plasma urate due to an X-linked recessive c.481G>T (p.A161S) HPRT gene mutation. He underwent muscle biopsy on suspicion of an underlying mitochondrial genetic defect, which revealed 15% COXdeficient fibres. Screens for mtDNA rearrangements and mtDNA depletion were negative, as was mtDNA genome sequencing of homogenate muscle DNA. Sequencing of individual, laser-captured COX-deficient fibres did however identify a novel tRNA mutation at high levels in all affected cells. The tRNA mutation was found to be present at surprisingly low levels (18%) in mature muscle, yet seg-
doi:10.1016/j.nmd.2009.06.064
G.P.3.07 Novel mutation in SUCLA2 gene: Encephalomyopathy, dystonia and deafness associated with mild methylmalonic aciduria and mtDNA depletions A.E.N. Nascimento Osorio1, A.N.S. Navarro-Sastre 2, J.C. Colomer 3, C.P. Paredes 3, A.G. Gutierrez 3, C.O. Ortez 3, M.V. Vilaseca 4, J.M. Montoya 5, T.R. Ribes 2 1 Hospital Sant Joan de Deu, Servei de Neurologia, Unitat de Patologia nuromuscular, Barcelona, Spain, 2 Instituto de Bioquimica Clinica y Genetica Molecular, Barcelona, Spain, 3 Hospital Sant Joan de Deu, Unitat de Patologia Neuromuscular, S. Neurologia, Barcelona, Spain, 4 Hospital Sant Joan de Deu, Bioquimica, Barcelona, Spain, 5 Universidad de Zaragoza, Zaragoza, Spain
doi:10.1016/j.nmd.2009.06.065
G.P.3.08 Myoclonic epilepsy, cortical dysplasia and mitochondrial complex I deficiency: A case report C. Nesti1, M. Mancuso 1, L. Petrozzi 1, F.M. Santorelli 2, A. Rocchi 1, G. Ali 3, A. Tessa 2, A. LoGerfo 1, A. Iudice 1, G. Siciliano 1