title: New genes and pathomechanisms in mitochondrial disorders unraveled by NGS technologies.
abstract: Next Generation Sequencing (NGS) technologies are revolutionizing the diagnostic screening for rare disease entities, including primary mitochondrial disorders, particularly those caused by nuclear gene defects. NGS approaches are able to identify the causative gene defects in small families and even single individuals, unsuitable for investigation by traditional linkage analysis. These technologies are contributing to fill the gap between mitochondrial disease cases defined on the basis of clinical, neuroimaging and biochemical readouts, which still outnumber by approximately 50% the cases for which a molecular-genetic diagnosis is attained. We have been using a combined, two-step strategy, based on targeted genes panel as a first NGS screening, followed by whole exome sequencing (WES) in still unsolved cases, to analyze a large cohort of subjects, that failed to show mutations in mtDNA and in ad hoc sets of specific nuclear genes, sequenced by the Sanger's method. Not only this approach has allowed us to reach molecular diagnosis in a significant fraction (20%) of these difficult cases, but it has also revealed unexpected and conceptually new findings. These include the possibility of marked variable penetrance of recessive mutations, the identification of large-scale DNA rearrangements, which explain spuriously heterozygous cases, and the association of mutations in known genes with unusual, previously unreported clinical phenotypes. Importantly, WES on selected cases has unraveled the presence of pathogenic mutations in genes encoding non-mitochondrial proteins (e.g. the transcription factor E4F1), an observation that further expands the intricate genetics of mitochondrial disease and suggests a new area of investigation in mitochondrial medicine. This article is part of a Special Issue entitled 'EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2-6, 2016', edited by Prof. Paolo Bernardi.
authors.affiliation: Unit of Molecular Neurogenetics, Fondazione IRCCS Istituto Neurologico 'Carlo Besta', 20126 Milan, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Legati
authors.affiliation: Mitochondrial Biology Unit, Medical Research Council, Cambridge CB2 0XY, UK.
authors.forename: Aurelio
authors.initials: A
authors.lastname: Reyes
authors.affiliation: Unit of Molecular Neurogenetics, Fondazione IRCCS Istituto Neurologico 'Carlo Besta', 20126 Milan, Italy.
authors.forename: Alessia
authors.initials: A
authors.lastname: Nasca
authors.affiliation: Unit of Molecular Neurogenetics, Fondazione IRCCS Istituto Neurologico 'Carlo Besta', 20126 Milan, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Invernizzi
authors.affiliation: Unit of Molecular Neurogenetics, Fondazione IRCCS Istituto Neurologico 'Carlo Besta', 20126 Milan, Italy.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Lamantea
authors.affiliation: Unit of Molecular Neurogenetics, Fondazione IRCCS Istituto Neurologico 'Carlo Besta', 20126 Milan, Italy.
authors.forename: Valeria
authors.initials: V
authors.lastname: Tiranti
authors.affiliation: Unit of Molecular Neurogenetics, Fondazione IRCCS Istituto Neurologico 'Carlo Besta', 20126 Milan, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Garavaglia
authors.affiliation: Unit of Molecular Neurogenetics, Fondazione IRCCS Istituto Neurologico 'Carlo Besta', 20126 Milan, Italy.
authors.forename: Costanza
authors.initials: C
authors.lastname: Lamperti
authors.affiliation: Unit of Child Neurology, Fondazione IRCCS Istituto Neurologico 'Carlo Besta', 20133 Milan, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Ardissone
authors.affiliation: Unit of Child Neurology, Fondazione IRCCS Istituto Neurologico 'Carlo Besta', 20133 Milan, Italy.
authors.forename: Isabella
authors.initials: I
authors.lastname: Moroni
authors.affiliation: Mitochondrial Biology Unit, Medical Research Council, Cambridge CB2 0XY, UK.
authors.forename: Alan
authors.initials: A
authors.lastname: Robinson
authors.affiliation: Unit of Molecular Neurogenetics, Fondazione IRCCS Istituto Neurologico 'Carlo Besta', 20126 Milan, Italy. Electronic address: dghezzi@istituto-besta.it.
authors.forename: Daniele
authors.initials: D
authors.lastname: Ghezzi
authors.affiliation: Mitochondrial Biology Unit, Medical Research Council, Cambridge CB2 0XY, UK. Electronic address: mdz21@mrc-mbu.cam.ac.uk.
authors.forename: Massimo
authors.initials: M
authors.lastname: Zeviani
mesh_terms: D000293:Adolescent; D000595:Amino Acid Sequence; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D004272:DNA, Mitochondrial / Q000235:genetics* / Q000378:metabolism; D004579:Electron Transport; D045222:Electron Transport Chain Complex Proteins / Q000235:genetics* / Q000378:metabolism; D059472:Exome; D005260:Female; D015870:Gene Expression; D006579:Heterozygote; D059014:High-Throughput Nucleotide Sequencing; D006720:Homozygote; D006801:Humans; D007223:Infant; D008297:Male; D008928:Mitochondria / Q000378:metabolism* / Q000473:pathology; D028361:Mitochondrial Diseases / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D008969:Molecular Sequence Data; D009154:Mutation; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D044767:Ubiquitin-Protein Ligases; D055815:Young Adult
chemical_list: D004272:DNA, Mitochondrial; D045222:Electron Transport Chain Complex Proteins; D012097:Repressor Proteins; C513814:E4F1 protein, human; D044767:Ubiquitin-Protein Ligases
keywords: E4F1; Mitochondrial disorders; Next Generation Sequencing; Whole Exome sequencing