Annual Report of Activities CNC 2008 - Center for Neuroscience and ...

3. Pediatric Research: metabolic disordersLuísa Diogo (CHC); Catarina Oliveira (CNC, FMUC); Manuela Grazina (CNC, FMUC)Mitochondrial respiratory chain diseases (MRCD) are a diverse group of disorders with a broad spectrumof clinical manifestations, characterised by defects in mitochondrial energetic function. Inherited defectscausing mitochondrial dysfunction can be due to mutations either in nuclear DNA (nDNA) ormitochondrial DNA (mtDNA). Each mitochondrion contains its own DNA that codes for 13 peptides ofthe mitochondrial respiratory chain (MRC) system, where the oxidative phosphorylation (OXPHOS)occurs, plus the two structural rRNAs and 22 tRNAs necessary for mtDNA genes expression. Novelconcepts of mitochondrial inheritance, such as mtDNA heteroplasmy, tissue distribution and thresholdeffect, have explained many of the clinical characteristics. Different gene mutations of mtDNA origin thatproduce MRC defects have been identified and have been classified as point mutations, large‐scalemtDNA deletions, duplications or insertions. Additionally, other mutations affecting nDNA genes (eithercoding for MRC subunits or assembly/mtDNA stability factors) have also been recently identified; inparticular, autosomically inherited disorders have been identified in cases with multiple mtDNAdeletions. The major laboratory criteria for the diagnosis of MRCD include: ragged red fibbers (RRF’s) onmuscle biopsy, lactic acidosis, a specific deficiency in a mitochondrial respiratory enzyme complex andnDNA/mtDNA abnormalities. However, not all MRCD cases display RRF’s, biochemical analyses ofmuscle tissue may show no apparent defects and, in a large proportion of patients with MRC enzymedeficiencies, no mutations have been found. Taking into account these facts, our main objective is toprovide tools for the diagnosis of MCRD and a better understanding of the pathogenic mechanismsleading to the clinical phenotypes. This will provide new insight into mitochondrial dysfunctions and willbe the basis for more rational therapies for the patients. The precise pathogenic mechanisms by whichthese biochemical abnormalities induce tissue dysfunction are not clearly understood and diagnosis ofthese disorders is complex, requiring specialised techniques and correlation between clinical andbiochemical/ genetic data.The mtDNA copy number/mutation quantification by real time PCR was initiated. One patient wasinvestigated, with collaboration of University of Newcastle upon Tyne, and a copy number variation wasdetected. This approach will be implemented for diagnosis and research purposes, and represents a majoradvance for our centre in this area.87We have continued the set up of the evaluation of Pyruvate dehydrogenase and Krebs cycle enzymeactivities for diagnostic and research purposes. The analysis of fumarase activity in lymphocytes isolatedfrom blood was performed in 4 control samples.PublicationsDiogo L, Grazina M, Garcia P, Rebelo O, Alte Veiga M, Cuevas J, Vilarinho L, Tavares Almeida I, Oliveira CRPediatric Mitochondrial Respiratory Chain Disorders in the Centro Region of Portugal. Pediatr. Neurol. (In press).AbstractsEstevinho E, Oliveira S, Pratas J, Simões M, Mendes C, Santos MJ, Oliveira M, Diogo L, Macário C,Oliveira CR, Grazina M (2008) Mitochondrial cardiomyopathies: biochemical and genetic heterogeneity.Journal of Inherited. Metabolic Disease 31 (S1): 203‐P, 52.Silva S, Robalo C, Garcia P, Grazina M, Oliveira CR, Diogo L (2008). West Syndrome and mitochondrialdysfunction. Journal of Inherited Metabolic Disease 31 (S1): 205‐P, 52.Neves N, Garcia P, Proença T, Baldeiras I, Grazina M, Vilarinho L, Oliveira CR, Diogo L (2008). WestSyndrome and mitochondrial dysfunction. Journal of Inherited Metabolic Disease 31 (S1): 224‐P, 57.