title: Pathogenic role of mtDNA duplications in mitochondrial diseases associated with mtDNA deletions.
abstract: We estimated the frequency of multiple mtDNA rearrangements by Southern blot in 32 patients affected by mitochondrial disorders associated with single deletions in order to assess genotype-phenotype correlations and elucidate the pathogenic significance of mtDNA duplications. Muscle in situ hybridization studies were performed in patients showing mtDNA duplications at Southern blot. We found multiple rearrangements in 12/32 (37.5%) patients; in particular, mtDNA duplications were detected in 4/4 Kearns-Sayre syndrome (KSS), in 1 Pearson's syndrome, in 1/3 encephalomyopathies with progressive external ophthalmoplegia (PEO), and in 2/23 PEO. In situ studies documented an exclusive accumulation of deleted mtDNAs in cytochrome c oxidase negative fibers of patients with mtDNA duplications. The presence of mtDNA duplications significantly correlated with onset of symptoms before age 15 and occurrence of clinical multisystem involvement. Analysis of biochemical data documented a predominant reduction of complex III in patients without duplications compared to patients with mtDNA duplications. Our data indicate that multiple mtDNA rearrangements are detectable in a considerable proportion of patients with single deletions and that mtDNA duplications do not cause any oxidative impairment. They more likely play a pathogenic role in the determination of clinical expression of mitochondrial diseases associated with single mtDNA deletions, possibly generating deleted mtDNAs in embryonic tissues by homologous recombination.
authors.affiliation: Neurological Institute, Catholic University of Rome, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Odoardi
authors.forename: Michele
authors.initials: M
authors.lastname: Rana
authors.forename: Aldobrando
authors.initials: A
authors.lastname: Broccolini
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Mirabella
authors.forename: Anna
authors.initials: A
authors.lastname: Modoni
authors.forename: Adele
authors.initials: A
authors.lastname: D'Amico
authors.forename: Manuela
authors.initials: M
authors.lastname: Papacci
authors.forename: Pietro
authors.initials: P
authors.lastname: Tonali
authors.forename: Serenella
authors.initials: S
authors.lastname: Servidei
authors.forename: Gabriella
authors.initials: G
authors.lastname: Silvestri
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D015139:Blotting, Southern; D002648:Child; D004272:DNA, Mitochondrial / Q000235:genetics; D003576:Electron Transport Complex IV / Q000378:metabolism; D005128:Eye Diseases / Q000235:genetics; D005260:Female; D017353:Gene Deletion; D020440:Gene Duplication; D005819:Genetic Markers; D005838:Genotype; D006801:Humans; D007231:Infant, Newborn; D007625:Kearns-Sayre Syndrome / Q000235:genetics; D008297:Male; D028361:Mitochondrial Diseases / Q000235:genetics*; D017237:Mitochondrial Encephalomyopathies / Q000235:genetics*; D010641:Phenotype
chemical_list: D004272:DNA, Mitochondrial; D005819:Genetic Markers; D003576:Electron Transport Complex IV