title: Pure and syndromic optic atrophy explained by deep intronic OPA1 mutations and an intralocus modifier.
abstract: The genetic diagnosis in inherited optic neuropathies often remains challenging, and the emergence of complex neurological phenotypes that involve optic neuropathy is puzzling. Here we unravel two novel principles of genetic mechanisms in optic neuropathies: deep intronic OPA1 mutations, which explain the disease in several so far unsolved cases; and an intralocus OPA1 modifier, which explains the emergence of syndromic 'optic atrophy plus' phenotypes in several families. First, we unravelled a deep intronic mutation 364 base pairs 3' of exon 4b in OPA1 by in-depth investigation of a family with severe optic atrophy plus syndrome in which conventional OPA1 diagnostics including gene dosage analyses were normal. The mutation creates a new splice acceptor site resulting in aberrant OPA1 transcripts with retained intronic sequence and subsequent translational frameshift as shown by complementary DNA analysis. In patient fibroblasts we demonstrate nonsense mediated messenger RNA decay, reduced levels of OPA1 protein, and impairment of mitochondrial dynamics. Subsequent site-specific screening of >360 subjects with unexplained inherited optic neuropathy revealed three additional families carrying this deep intronic mutation and a base exchange four nucleotides upstream, respectively, thus confirming the clinical significance of this mutational mechanism. Second, in all severely affected patients of the index family, the deep intronic mutation occurred in compound heterozygous state with an exonic OPA1 missense variant (p.I382M; NM_015560.2). The variant alone did not cause a phenotype, even in homozygous state indicating that this long debated OPA1 variant is not pathogenic per se, but acts as a phenotypic modifier if it encounters in trans with an OPA1 mutation. Subsequent screening of whole exomes from >600 index patients identified a second family with severe optic atrophy plus syndrome due to compound heterozygous p.I382M, thus confirming this mechanism. In summary, we provide genetic and functional evidence that deep intronic mutations in OPA1 can cause optic atrophy and explain disease in a substantial share of families with unsolved inherited optic neuropathies. Moreover, we show that an OPA1 modifier variant explains the emergence of optic atrophy plus phenotypes if combined in trans with another OPA1 mutation. Both mutational mechanisms identified in this study-deep intronic mutations and intragenic modifiers-might represent more generalizable mechanisms that could be found also in a wide range of other neurodegenerative and optic neuropathy diseases.
authors: 1 Molecular Genetics Laboratory, Institute for Ophthalmic Research, Centre for Ophthalmology, University of Tübingen, Röntgenweg 11, 72076 Tübingen, Germany2 Graduate School of Cellular and Molecular Neuroscience, University of Tübingen, Österbergstrasse 3, 72074 Tübingen, Germany.
authors: Tobias
authors: T
authors: Bonifert
authors: 3 Department of Neurodegenerative Diseases, Hertie-Institute for Clinical Brain Research, University of Tübingen, Hoppe-Seyler-Straße 3, 72076 Tübingen, Germany4 Centre for Neurodegenerative Diseases (DZNE), Helmholtz Association of German Research Centers, Otfried-Müller-Straße 27, 72076 Tübingen, Germany.
authors: Kathrin N
authors: KN
authors: Karle
authors: 5 University Eye Hospital, Centre for Ophthalmology, University of Tübingen, Schleichstrasse 12, 72076 Tübingen, Germany.
authors: Felix
authors: F
authors: Tonagel
authors: 6 Department of Neuroradiology, University of Tübingen, Hoppe-Seyler-Straße 3, 72076 Tübingen, Germany.
authors: Marion
authors: M
authors: Batra
authors: 7 CeGaT GmbH, Centre for Genomics and Transcriptomics, Paul-Ehrlich-Str. 17, 72076 Tübingen, Germany.
authors: Christian
authors: C
authors: Wilhelm
authors: 3 Department of Neurodegenerative Diseases, Hertie-Institute for Clinical Brain Research, University of Tübingen, Hoppe-Seyler-Straße 3, 72076 Tübingen, Germany4 Centre for Neurodegenerative Diseases (DZNE), Helmholtz Association of German Research Centers, Otfried-Müller-Straße 27, 72076 Tübingen, Germany.
authors: Yvonne
authors: Y
authors: Theurer
authors: 3 Department of Neurodegenerative Diseases, Hertie-Institute for Clinical Brain Research, University of Tübingen, Hoppe-Seyler-Straße 3, 72076 Tübingen, Germany4 Centre for Neurodegenerative Diseases (DZNE), Helmholtz Association of German Research Centers, Otfried-Müller-Straße 27, 72076 Tübingen, Germany.
authors: Caroline
authors: C
authors: Schoenfeld
authors: 8 Department of Orthopaedic Surgery, University Hospital Tübingen, Hoppe-Seyler-Str. 3, 72076 Tübingen, Germany.
authors: Torsten
authors: T
authors: Kluba
authors: 9 Department of Dermatology, University Hospital Tübingen, Röntgenweg 13/1, 72076 Tübingen, Germany.
authors: York
authors: Y
authors: Kamenisch
authors: 10 IRCCS Istituto delle Scienze Neurologiche di Bologna, Bellaria Hospital, Via Altura 3, 40139 Bologna, Italy11 Neurology Unit, Department of Biomedical and Neuromotor Sciences (DIBINEM), University of Bologna, Via Altura 3, 40139 Bologna, Italy.
authors: Valerio
authors: V
authors: Carelli
authors: 3 Department of Neurodegenerative Diseases, Hertie-Institute for Clinical Brain Research, University of Tübingen, Hoppe-Seyler-Straße 3, 72076 Tübingen, Germany4 Centre for Neurodegenerative Diseases (DZNE), Helmholtz Association of German Research Centers, Otfried-Müller-Straße 27, 72076 Tübingen, Germany.
authors: Julia
authors: J
authors: Wolf
authors: 12 Dr John T. Macdonald Foundation Department of Human Genetics and John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, 1501 NW 10 Ave, Miami, FL 33136, USA.
authors: Michael A
authors: MA
authors: Gonzalez
authors: 12 Dr John T. Macdonald Foundation Department of Human Genetics and John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, 1501 NW 10 Ave, Miami, FL 33136, USA.
authors: Fiorella
authors: F
authors: Speziani
authors: 3 Department of Neurodegenerative Diseases, Hertie-Institute for Clinical Brain Research, University of Tübingen, Hoppe-Seyler-Straße 3, 72076 Tübingen, Germany4 Centre for Neurodegenerative Diseases (DZNE), Helmholtz Association of German Research Centers, Otfried-Müller-Straße 27, 72076 Tübingen, Germany12 Dr John T. Macdonald Foundation Department of Human Genetics and John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, 1501 NW 10 Ave, Miami, FL 33136, USA.
authors: Rebecca
authors: R
authors: Schüle
authors: 12 Dr John T. Macdonald Foundation Department of Human Genetics and John P. Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, 1501 NW 10 Ave, Miami, FL 33136, USA.
authors: Stephan
authors: S
authors: Züchner
authors: 3 Department of Neurodegenerative Diseases, Hertie-Institute for Clinical Brain Research, University of Tübingen, Hoppe-Seyler-Straße 3, 72076 Tübingen, Germany4 Centre for Neurodegenerative Diseases (DZNE), Helmholtz Association of German Research Centers, Otfried-Müller-Straße 27, 72076 Tübingen, Germany.
authors: Ludger
authors: L
authors: Schöls
authors: 1 Molecular Genetics Laboratory, Institute for Ophthalmic Research, Centre for Ophthalmology, University of Tübingen, Röntgenweg 11, 72076 Tübingen, Germany wissinger@uni-tuebingen.de.
authors: Bernd
authors: B
authors: Wissinger
authors: 3 Department of Neurodegenerative Diseases, Hertie-Institute for Clinical Brain Research, University of Tübingen, Hoppe-Seyler-Straße 3, 72076 Tübingen, Germany4 Centre for Neurodegenerative Diseases (DZNE), Helmholtz Association of German Research Centers, Otfried-Müller-Straße 27, 72076 Tübingen, Germany.
authors: Matthis
authors: M
authors: Synofzik
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005091:Exons / Q000235:genetics; D005260:Female; D020558:GTP Phosphohydrolases / Q000235:genetics*; D018628:Gene Dosage / Q000235:genetics; D056426:Genetic Loci / Q000235:genetics; D014644:Genetic Variation; D015894:Genome, Human / Q000235:genetics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics*; D029241:Optic Atrophy, Autosomal Dominant / Q000145:classification / Q000235:genetics* / Q000473:pathology; D010375:Pedigree; D010641:Phenotype; D013577:Syndrome
chemical_list: D020558:GTP Phosphohydrolases; C415198:OPA1 protein, human
keywords: ataxia; cryptic exon; deep intronic mutation; genetic modifier; mitochondrial network