OPA1 Mutations Research Articles

Identification of copy number variation in the gene for autosomal dominant optic atrophy, OPA1, in a Chinese pedigree.

Autosomal dominant optic atrophy (ADOA) is an optic neuropathy characterized by bilateral optic nerve pallor and decreased visual acuity. It has been reported to be associated with two genes, OPA1, OPA3, and the OPA4, OPA5, and OPA8 loci. However, mutations in OPA1 constitute the most prevalent cause of ADOA. The purpose of this study was to identify the underlying genetic defect in a Chinese pedigree with ADOA. DNA from six members of a Chinese pedigree was collected for testing genomic and copy number variation (CNV) by targeted region capture and next generation sequencing (targeted NGS). A new developmental CNV detection method was applied to analyze the sequence data. Further verification of CNV was performed by real-time polymerase chain reaction (PCR). Three members of the pedigree with clinically diagnosed ADOA were screened for pathogenic genes related to ophthalmic genetic disease. No eligible pathogenic point mutations associated with ADOA disease-causing genes were found in pedigree members with ADOA. Upon further analysis for CNVs, we found a heterozygous deletion in exons 1-9 of OPA1, which was confirmed by real-time PCR. In this study we used a new developmental method to detect CNVs associated with ADOA in a Chinese pedigree. To our knowledge, this is the first case of ADOA caused by a CNV of the OPA1 gene in Chinese patients. The findings suggest that CNVs might be an important mutation type in Chinese patients with ADOA, and that CNV screening should be performed when point mutation screens are negative in these patients.

Improved locus-specific database for OPA1 mutations allows inclusion of advanced clinical data.

Autosomal-dominant optic atrophy (ADOA) is the most common inherited optic neuropathy, due to mutations in the optic atrophy 1 gene (OPA1) in about 60%-80% of cases. At present, the clinical heterogeneity of patients carrying OPA1 variants renders genotype-phenotype correlations difficulty. Since 2005, when we published the first locus-specific database (LSDB) dedicated to OPA1, a large amount of new clinical and genetic knowledge has emerged, prompting us to update this database. We have used the Leiden Open-Source Variation Database to develop a clinico-biological database, aiming to add clinical phenotypes related to OPA1 variants. As a first step, we validated this new database by registering several patients previously reported in the literature, as well as new patients from our own institution. Contributors may now make online submissions of clinical and molecular descriptions of phenotypes due to OPA1 variants, including detailed ophthalmological and neurological data, with due respect to patient anonymity. The updated OPA1 LSDB (http://opa1.mitodyn.org/) should prove useful for molecular diagnoses, large-scale variant statistics, and genotype-phenotype correlations in ADOA studies.

A recurrent deletion mutation in OPA1 causes autosomal dominant optic atrophy in a Chinese family.

Autosomal dominant optic atrophy (ADOA) is the most frequent form of hereditary optic neuropathy and occurs due to the degeneration of the retinal ganglion cells. To identify the genetic defect in a family with putative ADOA, we performed capture next generation sequencing (CNGS) to screen known retinal disease genes. However, six exons failed to be sequenced by CNGS in optic atrophy 1 gene (OPA1). Sequencing of those exons identified a 4 bp deletion mutation (c.2983-1_2985del) in OPA1. Furthermore, we sequenced the transcripts of OPA1 from the patient skin fibroblasts and found there is six-nucleotide deletion (c.2984-c.2989, AGAAAG). Quantitative-PCR and Western blotting showed that OPA1 mRNA and its protein expression have no obvious difference between patient skin fibroblast and control. The analysis of protein structure by molecular modeling suggests that the mutation may change the structure of OPA1 by formation of an alpha helix protruding into an existing pocket. Taken together, we identified an OPA1 mutation in a family with ADOA by filling the missing CNGS data. We also showed that this mutation affects the structural intactness of OPA1. It provides molecular insights for clinical genetic diagnosis and treatment of optic atrophy.

Mutation screening of mitochondrial DNA as well as OPA1 and OPA3 in a Chinese cohort with suspected hereditary optic atrophy.

Leber's hereditary optic atrophy (LHON) and autosomal dominant optic atrophy (DOA) are the two most common forms. The objective of this study was to define the fractional prevalence of LHON and DOA in a cohort of Chinese patients with suspected hereditary optic neuropathy. We recruited 520 unrelated patients with bilateral optic atrophy for genetic analysis: 174 patients had a positive family history of visual failure and 346 were sporadic cases. A total of 14 primary LHON-causing mtDNA mutations was screened by PCR-based sequencing methods for all patients except the individuals with a paternal family history. All coding exons and exon-intron boundaries of the OPA1 and OPA3 gene were screened for mutations by PCR-based DNA sequencing for all patients with paternal family history and for the LHON-negative patients. A large genomic DNA arrangement of the OPA1 gene was detected further by multiplex ligation probe amplification (MLPA) assay for the patients with paternal family history, but results were negative for the OPA1 and OPA3 mutation screenings. We found molecular defects in 323 (62%) of the 520 probands screened. Among these, 271 patients (83.9%) had an mtDNA mutation, 50 patients (15.5%) carried an OPA1 mutation, and 2 patients (0.6%) had an OPA3 mutation. Coexistence m.3460 G>A and m.11778G>A was found in one patient. We identified 40 intragenic mutations and six large genomic DNA arrangements of the OPA1 gene, 23 of which were novel. The LHON-mtDNA mutations are the most common genetic defects, followed by the OPA1 mutations, in this Chinese cohort.

Clinical and molecular genetic findings in autosomal dominant OPA3-related optic neuropathy.

Leber hereditary optic neuropathy and autosomal dominant optic atrophy are the two most common inherited optic neuropathies. The latter has been associated with mutations in the OPA1 and OPA3 genes. To date, only six families with OPA3-associated dominant optic atrophy have been reported. In order to identify additional families, we performed Sanger sequencing of the OPA3 gene in 75 unrelated optic neuropathy patients. Affected individuals from two families were found to harbour the c.313C > G, p.(Gln105Glu) change in heterozygous state; this genetic defect has been previously reported in four dominant optic atrophy families. Intra- and interfamilial variability in age of onset and presenting symptoms was observed. Although dominant OPA3 mutations are typically associated with optic atrophy and cataracts, the former can be observed in isolation; we report a case with no lens opacities at age 38. Conversely, it is important to consider OPA3-related disease in individuals with bilateral infantile-onset cataracts and to assess optic nerve health in those whose vision fail to improve following lens surgery. The papillomacular bundle is primarily affected and vision is typically worse than 20/40. Notably, we describe one subject who retained normal acuities into the fifth decade of life. The condition can be associated with extraocular clinical features: two affected individuals in the present study had sensorineural hearing loss. The clinical heterogeneity observed in the individuals reported here (all having the same genetic defect in OPA3) suggests that the molecular pathology of the disorder is likely to be complex.

Reply: Early-onset Behr syndrome due to compound heterozygous mutations in OPA1

Reply: Early-onset Behr syndrome due to compound heterozygous mutations in OPA1

Pure and syndromic optic atrophy explained by deep intronic OPA1 mutations and an intralocus modifier.

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.

Early Macular Retinal Ganglion Cell Loss in Dominant Optic Atrophy: Genotype-Phenotype Correlation

To assess the peripapillary retinal nerve fiber and macular retinal ganglion cell (RGC) loss in patients with dominant optic atrophy (DOA) stratified by OPA1 mutation type. Cross-sectional study. We studied 39 patients from 28 pedigrees with DOA harboring heterozygous mutations in the OPA1 gene along with 45 age-matched healthy subjects. The retinal nerve fiber layer (RNFL) and ganglion cell-inner plexiform layer (GC-IPL) of patients with DOA were evaluated by optical coherence tomography (OCT) and compared to those of controls. Patients' eyes were divided into 4 groups based on increasing severity of visual loss (DOA1 to DOA4) and were stratified by OPA1 mutation type. The average thicknesses of the RNFL and GC-IPL were smaller in patients with DOA than in healthy controls (P < 0.0001). RNFL analysis showed a significant reduction of the average, superior and inferior quadrants thicknesses in the DOA4 group compared to the DOA1 group (P= 0.001, P= 0.002 and P= 0.001, respectively). GC-IPL analysis showed a significant thinning in the superotemporal and superior sectors in the patients with DOA2 compared to those with DOA1 (P= 0.046 and P= 0.04, respectively). Stratifying by mutation type, average, superior and nasal RNFL thinning was significantly more severe in missense mutations and had a presumed dominant-negative effect compared to mutations causing haploinsufficiency. The present study demonstrates that in DOA, loss of macular RGCs is the earliest pathologic event, better reflected by GC-IPL measurements, whereas RNFL thickness is a measure of spared axons in late stages of the disease. Thus, mild cases (DOA2) show significant macular RGC loss as opposed to substantial maintenance of RNFL thickness, which is significantly decreased only in severe cases (DOA4). A clear genotype/phenotype correlation emerged, stratifying OCT measures by OPA1 mutation type, missense mutations being the most severe.

197th ENMC international workshop: Neuromuscular disorders of mitochondrial fusion and fission – OPA1 and MFN2 molecular mechanisms and therapeutic strategies: 26–28 April 2013, Naarden, The Netherlands

The 197th ENMC workshop entitled “Neuromuscular disorders of mitochondrial fusion and fission – OPA1 and MFN2 molecular mechanisms and therapeutic strategies” took place from the 26th to the 28th of April 2013 in Naarden, The Netherlands. A multidisciplinary group of 19 participants took part in this workshop, including 18 clinical and basic science researchers from six different countries (France, Germany, Italy, Spain, the United Kingdom (UK), and the United States of America), and one patient representative from CMT UK. The principal aim of this workshop was to establish an integrated research network in order to better understand the basic mechanisms responsible for the development of neuromuscular disease in patients harbouring pathogenic OPA1 and MFN2 mutations, which cause autosomal dominant optic atrophy (DOA) and axonal Charcot–Marie–Tooth disease (CMT2A), respectively [1,2].

Mutation analysis of seven known glaucoma-associated genes in Chinese patients with glaucoma.

To evaluate mutations in the MYOC, WDR36, OPTN, OPA1, NTF4, CYP1B1, and LTBP2 genes in a cohort of Chinese patients with primary glaucoma. Genomic DNA was prepared from 683 unrelated patients, including 50 with primary congenital glaucoma, 104 with juvenile open-angle glaucoma (JOAG), 186 with primary open-angle glaucoma (POAG), and 343 with primary angle-closure glaucoma (PACG). Mutations in the seven genes in 257 patients (36 with JOAG, 89 with POAG, and 132 with PACG) were initially analyzed by exome sequencing and then confirmed by Sanger sequencing. In addition, Sanger sequencing was used to detect MYOC mutations in the remaining 426 patients. Exome sequencing identified 19 mutations (6 in MYOC, 9 in WDR36, 3 in OPA1, and 1 in OPTN) in 20 of 257 patients, including 4 patients with JOAG, 8 patients with POAG, and 8 patients with PACG. No mutation was detected in the other three genes. In addition, Sanger sequencing detected additional MYOC mutations in 5 of the remaining 426 patients, including 3 patients with JOAG and 2 patients with POAG. Twenty-two mutations in MYOC, WDR36, OPA1, and OPTN were detected in 25 of the 683 patients with primary glaucoma, including nine MYOC mutations in 11 patients, nine WDR36 mutations in 11 patients, three OPA1 mutations in 3 patients, and one OPTN mutation in a patient who also carried a MYOC mutation. Eight mutations in MYOC, WDR36, and OPA1 in 8 of the 343 PACG patients are of uncertain significance and need to be analyzed further.

White Matter Microstructure Abnormalities in Patients with Dominant Optic Atrophy and OPA1 Mutations (S39.002)

White Matter Microstructure Abnormalities in Patients with Dominant Optic Atrophy and OPA1 Mutations (S39.002)

Two novel compound heterozygous mutations in OPA3 in two siblings with OPA3-related 3-methylglutaconic aciduria

OPA3-related 3-methylglutaconic aciduria, or Costeff Optic Atrophy syndrome, is a neuro-ophthalmologic syndrome of early-onset bilateral optic atrophy and later-onset spasticity, and extrapyramidal dysfunction. Urinary excretion of 3-methylglutaconic acid and of 3-methylglutaric acid is markedly increased. OPA3-related 3-methylglutaconic aciduria is due to mutations in the OPA3 gene located at 19q13.2–13.3. Here we describe two siblings with novel compound heterozygous variants in OPA3: c.1A>G (p.1M>V) in the translation initiation codon in exon 1 and a second variant, c.142+5G>C in intron 1. On cDNA sequencing the c.1A>G appeared homozygous, indicating that the allele without the c.1A>G variant is degraded. This is likely due to an intronic variant; possibly the IVS1+5 splice site variant. The older female sibling initially presented with motor developmental delay and vertical nystagmus during her first year of life and was diagnosed subsequently with optic atrophy. Her brother presented with mildly increased hip muscle tone followed by vertical nystagmus within the first 6months of life, and was found to have elevated urinary excretion of 3-methylglutaconic acid and 3-methylglutaric acid, and optic atrophy by 1.5years of age. Currently, ages 16 and 7, both children exhibit ataxic gaits and dysarthric speech. Immunofluorescence studies on patient's cells showed fragmented mitochondrial morphology. Thus, though the exact function of OPA3 remains unknown, our experimental results and clinical summary provide evidence for the pathogenicity of the identified OPA3 variants and provide further evidence for a mitochondrial pathology in this disease.

Novel OPA1 mutation featuring spastic paraparesis and intestinal dysmotility

A 58-year-old man with optic atrophy, spastic paraparesis, axonal sensorimotor peripheral neuropathy and intestinal dysmotility harbors a novel heterozygous missense mutation in the mitochondrial import signal peptide of OPA1. The case underscores the role of OPA1 in the pathogenesis of spastic paraparesis, so far reported only in very few cases, and it adds intestinal dysmotility to the spectrum of adult-onset clinical manifestation of OPA1-associated disease.

First Cases of Dominant Optic Atrophy in Saudi Arabia

Fifty to 60% of patients with dominant optic atrophy (DOA) have mutations of the OPA1 gene, which encodes dynamin-related GTPase, a protein of the internal mitochondrial membrane. To date, more than 200 OPA1 mutations in the OPA1 gene have been described. However, DOA is genetically heterogeneous with certain families linked to other chromosomal loci, that is, OPA3, OPA4, OPA5, and OPA7. This study describes a clinical series of 40 patients from Saudi Arabia with a positive DOA phenotype (i.e., decreased visual acuity during the first 2 decades of life, temporal or global optic disc pallor, and absence of other neurological or ophthalmological diseases that could explain the optic neuropathy) who underwent molecular genetic testing for OPA1 (and, in some cases, for OPA3). This study describes for the first time 4 OPA1 mutations in DOA patients from Saudi Arabia, including 2 novel OPA1 mutations in 2 different patients. The question remains whether certain patients in Saudi Arabia with a clearly defined DOA phenotype may be due to mutations in chromosomal loci other than OPA1 and OPA3. It is likely that genetic alterations associated with different loci will be discovered in the future.

A novel heterozygous OPA3 mutation located in the mitochondrial target sequence results in altered steady-state levels and fragmented mitochondrial network

BackgroundMutations in OPA3 have been reported in patients with autosomal dominant optic atrophy plus cataract and Costeff syndrome. Here, we report the results of a comprehensive study on OPA3 mutations,...

Extraocular Muscle Atrophy and Central Nervous System Involvement in Chronic Progressive External Ophthalmoplegia

BackgroundChronic progressive external ophthalmoplegia (CPEO) is a classical mitochondrial ocular disorder characterised by bilateral progressive ptosis and ophthalmoplegia. These ocular features can develop either in isolation or in association with other prominent neurological deficits (CPEO+). Molecularly, CPEO can be classified into two distinct genetic subgroups depending on whether patients harbour single, large-scale mitochondrial DNA (mtDNA) deletions or multiple mtDNA deletions secondary to a nuclear mutation disrupting mtDNA replication or repair. The aim of this magnetic resonance imaging (MRI) study was to investigate whether the ophthalmoplegia in CPEO is primarily myopathic in origin or whether there is evidence of contributory supranuclear pathway dysfunction.MethodsTen age-matched normal controls and twenty patients with CPEO were recruited nine patients with single, large-scale mtDNA deletions and eleven patients with multiple mtDNA deletions secondary to mutations in POLG, PEO1, OPA1, and RRM2B. All subjects underwent a standardised brain and orbital MRI protocol, together with proton magnetic resonance spectroscopy in two voxels located within the parietal white matter and the brainstem.ResultsThere was evidence of significant extraocular muscle atrophy in patients with single or multiple mtDNA deletions compared with controls. There was no significant difference in metabolite concentrations between the patient and control groups in both the parietal white matter and brainstem voxels. Volumetric brain measurements revealed marked cortical and cerebellar atrophy among patients with CPEO+ phenotypes.ConclusionThe results of this study support a primary myopathic aetiology for the progressive limitation of eye movements that develops in CPEO.

Sensorineural hearing loss in OPA1‐linked disorders

AbstractAbout 20% of OPA1 mutation carriers have complicated forms of dominant optic atrophy associating extra‐ocular features. Reviewing the files of 327 patients with an OPA1 mutation, we found 21 deaf patients (6.4%). In 10 patients deafness was detected under age 20, in 3 patients over age 20 and in 8 patients the age of onset was unknown. The severity of deafness ranged from mild and moderate. Audiological tests supported the diagnosis of auditory neuropathy in 8 cases. Seven different OPA1 mutations were identified in deaf patients. Three mutations, p.Arg445His, p.Gly401Asp and p.Leu243*, have been previously reported in patients with deafness. Two mutations, p.Val291_Phe328del and p.Ile463_Phe464dup, have been reported in patients with DOA without deafness. Finally, two novel OPA1 mutations, p.Arg437Glu and p.Ala357Leufs*4 were found. In the majority of patients with DOA and deafness, visual impairment occurred during the first decade while deafness appeared later. However, in 54% of patients deafness started prior to visual abnormalities. These observations suggest that audition should be carefully tested, including a specific search for auditory neuropahy in OPA1 mutation carriers.

Genetic analyses of autosomal optic neuropathies reveal novel physiopathological pathways involved in optic nerve degeneration

AbstractAutosomal Optic Neuropathies (AON) are rare mitochondrial diseases affecting the retinal ganglion cells that form the optic nerve and transduce the visual informations from the retina to the brain. They are heterogeneous inherited diseases with dominant – the most abundant ‐ and recessive forms, for which only three genes have so far been identified, OPA1, OPA3 and OPA7. Together, mutations in these genes account for less than 50% of patients with an ascertained clinical diagnosis, OPA1 being by far the most frequent gene involved. To gain insight in the genetic diagnosis of AON, we performed whole exome sequencing on dominant and recessive families, for which we excluded mutation in OPA1, 3 and 7. Results identified some novel genes, all encoding mitochondrial matricial proteins. Importantly none encodes protein embedded in the inner mitochondrial membrane, as are OPA1, 3 and 7, but all have a function related to the lipid and protein composition of this membrane. Thus these results put emphasis on novel pathophysiological mechanisms involved in retinal ganglion cells degeneration, again pointing on the absolute requirement to maintain the inner mitochondrial integrity to preserve optic nerve function and survival.

The expanding clinical spectrum of dominant optic atrophy

AbstractAutosomal dominant optic atrophy (DOA) is the most common inherited optic nerve disorder in the population and OPA1 is the major causative gene, accounting for about 60% of families. Visual loss starts in early childhood secondary to the highly tissue‐specific loss of one cell type – the retinal ganglion cell. Although progressive visual failure remains the defining feature of DOA, we recently described the expanding phenotypic spectrum associated with OPA1 disease. Up to 20% of mutational carriers developed a more severe “DOA+” phenotype characterised by prominent neuromuscular features such as deafness, myopathy, peripheral neuropathy, ataxia, and chronic progressive external ophthalmoplegia. Interestingly, we found a three‐fold increased risk of developing the more severe DOA+ phenotype with missense OPA1 mutations involving the GTPase domain compared with other mutational subgroups. Histochemical and molecular characterisation of skeletal muscle biopsies revealed the presence of cytochrome c oxidase deficient fibres and clear evidence of mitochondrial DNA instability. Dissecting the disease mechanisms leading to optic atrophy and multisystem tissue involvement in DOA will have important therapeutic implications.

A Novel OPA3 Mutation Revealed by Exome Sequencing

We sought to unravel the genetic cause in a consanguineous Pakistani family with a complex neurological phenotype. Neurological and ophthalmological examination, including videotaping and fundoscopy, and genetic investigations, including homozygosity mapping and exome sequencing, were performed at the University of the Punjab and the University of Lübeck. Participants included 2 severely affected cousins from consanguineous parents, 10 of their reportedly unaffected relatives, and 342 Pakistani controls. Motor symptoms in the 2 patients started at the age of 3 to 4 years and included chorea, cerebellar ataxia, dystonia, and pyramidal tract signs. Genome-wide genotyping delineated 2 regions of homozygosity on chromosomes 13q12.11 to 13q12.13 and 19q12 to 19q13.41. Exome sequencing revealed 2 rare, homozygous variants (c.32 T>A [p.L11Q] in OPA3 and c.941 C>G [p.A314G] in TSHZ3) that segregated with the disease. Only the OPA3 variant was absent in the control subjects and predicted to be damaging. Subsequent ophthalmological assessment revealed bilateral optic atrophy in both patients. Mutations in OPA3 have been reported in Costeff optic atrophy syndrome. We identify a novel missense mutation in OPA3 as the cause of a complex neurological disorder, expanding the OPA3 -linked phenotype by early-onset pyramidal tract signs and marked lower limb dystonia. Investigation of optic atrophy was initiated only after genetic analysis, a phenomenon referred to as reverse phenotyping.