Fourteen novel OPA1 mutations in autosomal dominant optic atrophy including two de novo mutations in sporadic optic atrophy

The OPA1 gene, encoding a dynamin-related GTPase that plays a role in mitochondrial biogenesis, is implicated in most cases of autosomal dominant optic atrophy (ADOA). Sixty-nine pathogenic OPA1 mutations have been reported so far. Most of these are truncating mutations located in the GTPase domain coding region (exons 8-16) and at the 3'-end (exons 27-28). We screened 44 patients with typical ADOA using PCR-sequencing. We also tested 20 sporadic cases of bilateral optic atrophy compatible with ADOA. Of the 18 OPA1 mutations found, 14 have never been previously reported. The novel mutations include one nonsense mutation, 3 missense mutations, 6 deletions, one insertion and 3 exon-skipping mutations. Two of these are de novo mutations, which were found in 2 patients with sporadic optic atrophy. The recurrent c.2708_2711delTTAG mutation was found in 2 patients with a severe congenital presentation of the disease. These results suggest that screening for OPA1 gene mutations may be useful for patients with optic atrophy who have no affected relatives, or when the presentation of the disease is atypical as in the case of early onset optic atrophy.     

OPA1-related dominant optic atrophy is not strongly influenced by mitochondrial DNA background

Background  

Leber's hereditary optic neuropathy (LHON) and autosomal dominant optic atrophy (ADOA) are the most frequent forms of hereditary optic neuropathies. LHON is associated with mitochondrial DNA (mtDNA) mutations whereas ADOA is mainly due to mutations in the OPA1 gene that encodes a mitochondrial protein involved in the mitochondrial inner membrane remodeling. A striking influence of mtDNA haplogroup J on LHON expression has been demonstrated and it has been recently suggested that this haplogroup could also influence ADOA expression. In this study, we have tested the influence of mtDNA backgrounds on OPA1 mutations.     

常染色体显性视神经萎缩的分子遗传学研究进展

常染色体显性视神经萎缩 (Autosomal Dominant Optic Atrophy , ADOA), 亦称Kjer型，是一种常见的遗传性视神经病变。该病常在儿童期发病（平均发病年龄为7岁），发病率约1:10 000-1:50 000，表现为隐匿性渐进性视力减退，双颞侧视盘苍白，中心或旁中心暗点，色觉障碍(常表现为蓝黄色盲)。组织病理学表现为：视网膜神经节细胞退行性变。 OPA1编码一种保守的动力相关GTPase，OPA1突变是ADOA发病的主要原因，目前已发现117个ADOA相关OPA1突变，包括：31.6%缺失和插入突变， 16.2%无义突变，25.6%错义突变和28.8%剪接突变。这些突变分布于OPA1基因编码区，但多数位于GTPase区。另外，本病还与OPA3 (19q13.2-q13.3)、OPA4 (18q12.2-12.3)及OPA5 (22q12.1-q13.1)基因突变有关。个体间的表型差异表明：其他遗传因素，个人因素以及环境因素可能与ADOA发病有关。     

A family with X-linked optic atrophy linked to the OPA2 locus Xp11.4-Xp11.2

Autosomal dominant optic atrophy (ADOA) is the most common inherited optic atrophy. Clinical features of ADOA include a slowly progressive bilateral loss of visual acuity, constriction of peripheral visual fields, central scotomas, and color vision abnormalities. Although ADOA is the most commonly inherited optic atrophy, autosomal recessive, X-linked, mitochondrial, and sporadic forms have also been reported. Four families with X-linked optic atrophy (XLOA) were previously described. One family was subsequently linked to Xp11.4-Xp11.2 (OPA2). This investigation studied one multi-generation family with an apparently X-linked form of optic atrophy and compared their clinical characteristics with those of the previously described families, and determined whether this family was linked to the same genetic locus. Fifteen individuals in a three-generation Idaho family underwent complete eye examination, color vision testing, automated perimetry, and fundus photography. Polymorphic markers were used to genotype each individual and to determine linkage. Visual acuities ranged from 20/30 to 20/100. All affected subjects had significant optic nerve pallor. Obligate female carriers were clinically unaffected. Preliminary linkage analysis (LOD score = 1.8) revealed that the disease gene localized to the OPA2 locus on Xp11.4-Xp11.2. Four forms of inherited optic neuropathy, ADOA, autosomal recessive optic atrophy (Costeff Syndrome), Leber hereditary optic neuropathy, and Charcot-Marie-Tooth disease with optic atrophy, are associated with mitochondrial dysfunction. Future identification of the XLOA gene will reveal whether this form of optic atrophy is also associated with a mitochondrial defect. Identification of the XLOA gene will advance our understanding of the inherited optic neuropathies and perhaps suggest treatments for these diseases. An improved understanding of inherited optic neuropathies may in turn advance our understanding of acquired optic nerve diseases, such as glaucoma and ischemic optic neuropathy.     

Genomic deletions in <Emphasis Type="Italic">OPA1</Emphasis> in Danish patients with autosomal dominant optic atrophy

Background  

Autosomal dominant optic atrophy (ADOA, Kjer disease, MIM #165500) is the most common form of hereditary optic neuropathy. Mutations in OPA1 located at chromosome 3q28 are the predominant cause for ADOA explaining between 32 and 89% of cases. Although deletions of OPA1 were recently reported in ADOA, the frequency of OPA1 genomic rearrangements in Denmark, where ADOA has a high prevalence, is unknown. The aim of the study was to identify copy number variations in OPA1 in Danish ADOA patients.     

eOPA1: an online database for OPA1 mutations

Autosomal dominant optic atrophy (ADOA), also known as Kjer disease, is characterized by moderate to severe loss of visual acuity with an insidious onset in early childhood, blue-yellow dyschromatopsia, and central scotoma. An optic atrophy gene, called OPA1, has been identified in most cases of the disease. A total of 83 OPA1 mutations, often family-specific, have been reported so far, and the observations support the hypothesis that haploinsufficiency and the functional loss of a single allele may lead to ADOA. We have developed a new locus-specific database (LSDB), eOPA1 (http://lbbma.univ-angers.fr/eOPA1/) aimed at collecting published and unpublished sequence variations in OPA1. The database has been designed to incorporate new submissions rapidly and will provide a secured online catalog of OPA1 mutations and nonpathogenic sequence variants (NPSVs). The LSDB should prove useful for molecular diagnosis, large-scale mutation statistics, and the determination of original genotype-phenotype correlations in studies on ADOA.     

Opa1 deficiency in a mouse model of autosomal dominant optic atrophy impairs mitochondrial morphology, optic nerve structure and visual function

OPA1 is a ubiquitously expressed, nuclear dynamin-related GTPase, targeted to the inner mitochondrial membrane, which plays a role in mitochondrial fusion. Mutations in the OPA1 gene on chromosome 3q28-qter are associated with autosomal dominant optic atrophy (ADOA), the most common inherited optic neuropathy, in which retinal ganglion cells (RGCs) are lost and visual acuity is impaired from an early age. We have generated a novel ENU-induced mutant mouse carrying a protein-truncating nonsense mutation in opa1 in order to explore the pathophysiology of ADOA. The heterozygous mutation, B6; C3-Opa1(Q285STOP), located in exon 8 immediately before the central dynamin-GTPase, leads to approximately 50% reduction in opa1 protein in retina and all tissues on western analysis. The homozygous mutation is embryonic lethal by 13.5 days post coitum, demonstrating the importance of Opa1 during early development. Fibroblasts taken from adult heterozygous mutant mice show an apparent alteration in morphology, with an increase in mitochondrial fission and fragmentation. Heterozygous mutants show a slow onset of degeneration in the optic nerve electron microscopy. Furthermore, they demonstrate a functional reduction in visual function on testing with the optokinetic drum and the circadian running wheel. These findings indicate that the opa1 GTPase contains crucial information required for the survival of RGCs and that Opa1 is essential for early embryonic survival. The Opa1 +/- mice described here provide a means to directly investigate the cellular pathophysiology of OPA1 ADOA.     

Autosomal dominant optic atrophy associated with hearing impairment and impaired glucose regulation caused by a missense mutation in the WFS1 gene

Autosomal dominant optic atrophy (ADOA) is genetically heterogeneous, with OPA1 on 3q28 being the most prevalently mutated gene. Additional loci are OPA3, OPA4, and OPA5, located at 19q13.2, 18q12.2, and 22q12.1–q13.1, respectively. Mutations in the WFS1 gene, at 4p16.3, are associated with either optic atrophy (OA) as part of the autosomal recessive Wolfram syndrome or with autosomal dominant progressive low frequency sensorineural hearing loss (LFSNHL) without any ophthalmological abnormalities. Linkage and sequence mutation analyses of the ADOA candidate genes OPA1, OPA3, OPA4, and OPA5, including the genes WFS1, GJB2, and GJB6 associated with recessive inherited OA or dominant LFSNHL, were performed. We identified one novel WFS1 missense mutation E864K, c.2590G→A in exon 8 that co‐segregates with ADOA combined with hearing impairment and impaired glucose regulation. This is the first example of autosomal dominant optic atrophy and hearing loss associated with a WFS1 mutation, supporting the notion that mutations in WFS1 as well as in OPA1 may lead to ADOA combined with impaired hearing.     

The dynamin-related mouse mitochondrial GTPase OPA1 alters the structure of the mitochondrial inner membrane when exogenously introduced into COS-7 cells

Mutations in the dynamin family GTPase OPA1 are reportedly the cause of autosomal dominant optic atrophy, the most frequently occurring form of hereditary optic neuropathy. But although the involvement of structural abnormalities of the enzyme in this neurodegenerative disease is clear, little is known about the cell biological and biochemical functions of OPA1. Therefore, to better understand the pathogenesis of autosomal dominant optic atrophy, we precisely analyzed the effects of exogenously introducing mouse OPA1 (mOPA1) on mitochondrial morphology in COS-7 cells. We found that exogenously introducing wild type mOPA1 caused the mitochondria to become fragmented, and moreover caused the intermembrane space to accumulate on one side of the ring-shaped mitochondrial fragments. Immunoelectron microscopic observation of the mOPA1 transfectants confirmed that the structure of the mitochondrial inner membrane had changed dramatically, accumulating on one side of the mitochondrial structures. When cells were transfected with mOPA1 containing a loss of function mutation (K301A) within the G1 GTP-binding domain, mitochondrial fragmentation still occurred. The markers for intermembrane space and matrix showed the similar morphology, which was distinctly different from the finding obtained with wild type mOPA1 transfectants. Notably, we also observed that the effect of two OPA1 missense mutations (E270K and D273A) associated with autosomal dominant optic atrophy elicit effects similar to those seen with the dominant negative K301A mutant.     

Molecular screening of 980 cases of suspected hereditary optic neuropathy with a report on 77 novel OPA1 mutations

We report the results of molecular screening in 980 patients carried out as part of their work‐up for suspected hereditary optic neuropathies. All the patients were investigated for Leber's hereditary optic neuropathy (LHON) and autosomal dominant optic atrophy (ADOA), by searching for the ten primary LHON‐causing mtDNA mutations and examining the entire coding sequences of the OPA1 and OPA3 genes, the two genes currently identified in ADOA. Molecular defects were identified in 440 patients (45% of screened patients). Among these, 295 patients (67%) had an OPA1 mutation, 131 patients (30%) had an mtDNA mutation, and 14 patients (3%), belonging to three unrelated families, had an OPA3 mutation. Interestingly, OPA1 mutations were found in 157 (40%) of the 392 apparently sporadic cases of optic atrophy. The eOPA1 locus‐specific database now contains a total of 204 OPA1 mutations, including 77 novel OPA1 mutations reported here. The statistical analysis of this large set of mutations has led us to propose a diagnostic strategy that should help with the molecular work‐up of optic neuropathies. Our results highlight the importance of investigating LHON‐causing mtDNA mutations as well as OPA1 and OPA3 mutations in cases of suspected hereditary optic neuropathy, even in absence of a family history of the disease. © 2009 Wiley‐Liss, Inc.     

High frequency of OPA1 mutations causing high ADOA prevalence in south-eastern Sicily, Italy

Optic atrophy type 1 (OPA1) gene mutation causes autosomal dominant optic atrophy (ADOA, MIM #165500). Prevalence of ADOA ranges from 1:50,000 in most populations to 1:12,000 in Denmark. Seventy members of nine families were analysed for the presence of OPA1 gene mutations by polymerase chain reaction (PCR) and direct sequencing. We identified three OPA1 gene mutations in 48 patients with variable signs of optic atrophy. Two mutations, c.784-21_784-22insAluYb8 and c.876_878delTGT, were found in two different families. The third mutation, c.869G>A, was found in 28 patients from seven families. The haplotype analysis data suggested that the c.869G>A mutation is a founder mutation. Our main result suggests a higher ADOA prevalence in south-eastern Sicily than previously found in Denmark. This is because of not only the founder effect but also to the presence of three different mutations in the geographical area of the study. Our hypothesis is that a combination of social pressure because of blindness and migration factors is involved. In fact, in Siracusa, a provincial capital in south-eastern Sicily, St. Lucy, the patron saint of the blind was born and died.     

Exome sequencing identifies novel missense and deletion variants in RTN4IP1 associated with optic atrophy,global developmental delay,epilepsy, ataxia,and choreoathetosis

Inherited optic neuropathies (IONs) are neurodegenerative disorders characterized by optic atrophy with or without extraocular manifestations. Optic atrophy‐10 (OPA10) is an autosomal recessive ION recently reported to be caused by mutations in RTN4IP1, which encodes reticulon 4 interacting protein 1 (RTN4IP1), a mitochondrial ubiquinol oxydo‐reductase. Here we report novel compound heterozygous mutations in RTN4IP1 in a male proband with developmental delay, epilepsy, optic atrophy, ataxia, and choreoathetosis. Workup was notable for transiently elevated lactate and lactate‐to‐pyruvate ratio, brain magnetic resonance imaging with optic atrophy and T2 signal abnormalities, and a nondiagnostic initial genetic workup, including chromosomal microarray and mitochondrial panel testing. Exome sequencing identified a paternally inherited missense variant (c.263T>G, p.Val88Gly) predicted to be deleterious and a maternally inherited deletion encompassing RTN4IP1. To our knowledge, this is the first report of a non‐single nucleotide pathogenic variant associated with OPA10. This case highlights the expanding phenotypic spectrum of OPA10, the association between “syndromic” cases and severe RTN4IP1 mutations, and the importance of nonbiased genetic testing, such as ES, to analyze multiple genes and variants types, in patients suspected of having genetic disease.     

Identification of p.A684V missense mutation in the WFS1 gene as a frequent cause of autosomal dominant optic atrophy and hearing impairment

Optic atrophy (OA) and sensorineural hearing loss (SNHL) are key abnormalities in several syndromes, including the recessively inherited Wolfram syndrome, caused by mutations in WFS1. In contrast, the association of autosomal dominant OA and SNHL without other phenotypic abnormalities is rare, and almost exclusively attributed to mutations in the Optic Atrophy-1 gene (OPA1), most commonly the p.R445H mutation. We present eight probands and their families from the US, Sweden, and UK with OA and SNHL, whom we analyzed for mutations in OPA1 and WFS1. Among these families, we found three heterozygous missense mutations in WFS1 segregating with OA and SNHL: p.A684V (six families), and two novel mutations, p.G780S and p.D797Y, all involving evolutionarily conserved amino acids and absent from 298 control chromosomes. Importantly, none of these families harbored the OPA1 p.R445H mutation. No mitochondrial DNA deletions were detected in muscle from one p.A684V patient analyzed. Finally, wolframin p.A684V mutant ectopically expressed in HEK cells showed reduced protein levels compared to wild-type wolframin, strongly indicating that the mutation is disease-causing. Our data support OA and SNHL as a phenotype caused by dominant mutations in WFS1 in these additional eight families. Importantly, our data provide the first evidence that a single, recurrent mutation in WFS1, p.A684V, may be a common cause of ADOA and SNHL, similar to the role played by the p.R445H mutation in OPA1. Our findings suggest that patients who are heterozygous for WFS1 missense mutations should be carefully clinically examined for OA and other manifestations of Wolfram syndrome.     

OPA1 mutations and mitochondrial DNA haplotypes in autosomal dominant optic atrophy.

PURPOSE: Autosomal dominant optic atrophy is a form of blindness, due in part to mutations affecting the mitochondrial-targeted OPA1 gene product. Both OPA1-positive and OPA1-negative families exhibit variable expressivity and incomplete penetrance. The purpose of this study was therefore to determine if the background mtDNA genotype acts as a genetic modifier for the expression of this disease. METHODS: To find novel pathogenic OPA1 mutations, we performed complete OPA1 gene exon sequencing in 30 patients. To assess the possibility that mitochondrial DNA haplotype acts as a genetic modifier, we determined the mitochondrial DNA haplotype in 29 Caucasian OPA1-positive and OPA1-negative patients. Deviations in haplotype distribution between patient and control groups were determined by statistical means. RESULTS: Seven new pathogenic OPA1 mutations were found. Most were detected in the mitochondrial targeting N-terminus or in the coiled-coil domain at the C-terminus. Mitochondrial DNA haplotype analysis indicated that the European haplogroup distribution was different between Caucasian patients and controls. Further, haplogroup J was three-fold over-represented in OPA1-negative patients. CONCLUSIONS: Overall, our results support haploinsufficiency as a genetic mechanism in OPA1-positive cases and also suggest that mtDNA genetic background may influence disease expression in a subset of cases.     

Dominant optic atrophy in Denmark - report of 15 novel mutations in OPA1, using a strategy with a detection rate of 90 %

ABSTRACT: BACKGROUND: Investigation of the OPA1 mutation spectrum in autosomal dominant optic atrophy (ADOA) in Denmark. METHODS: Index patients from 93 unrelated ADOA families were assessed for a common Danish founder mutation (c.2826_2836delinsGGATGCTCCA) inOPA1. If negative, direct DNA sequencing of the coding sequence and multiplex ligation-dependent probe amplification (MLPA) were performed. Results from MLPA analysis have been previously reported. Haplotype analysis was carried out analysing single nucleotide polymorphisms (SNP). Retrospective clinical data were retrieved from medical files. RESULTS: Probably causative mutations were identified in 84 out of 93 families (90 %) including 15 novel mutations. Three mutations c.983A > G, c.2708_2711delTTAG and c.2826_2836delinsGGATGCTCCA, were responsible for ADOA in10, 11 and 28 families, respectively, corresponding to 11 %, 12 % and 30 %. A common haplotype in nine of ten c.983A > G families suggests that they descend from a single founder. The c.2708_2711delTTAG mutation was present on at least two haplotypes and has been repeatedly reported in various ethnic groups,thus represents a mutational hotspot. Clinical examinations of index patients with the two latter mutations demonstrated large inter- and intra-familial variations apparently. CONCLUSIONS: Genetic testing for OPA1mutations assist in the diagnosis. We have identified mutations in OPA1 in 90 % of families including 15 novel mutations. Both DNA sequencing and MLPA analysis are necessary to achieve a high detection rate. More than half of the affected families in Denmark are represented by three common mutations, at least two of which are due to a founder effect, which may account for the high prevalence of ADOA in Denmark.     

A clinically complex form of dominant optic atrophy (OPA8) maps on chromosome 16

Dominant optic atrophy (DOA) is genetically heterogeneous and pathogenic mutations have been identified in the OPA1 and OPA3 genes, both encoding for mitochondrial proteins. We characterized clinical and laboratory features in a large OPA1-negative family with complicated DOA. Search for mitochondrial dysfunction was performed by studying muscle biopsies, fibroblasts, platelets and magnetic resonance (MR) spectroscopy. Genetic investigations included mitochondrial DNA (mtDNA) analysis, linkage analysis, copy number variation (CNV) analysis and candidate gene screening. Optic neuropathy was undistinguishable from that in OPA1-DOA and frequently associated with late-onset sensorineural hearing loss, increases of central conduction times at somato-sensory evoked potentials and various cardiac abnormalities. Serum lactic acid after exercise, platelet respiratory complex activities, adenosine triphosphate (ATP) content in fibroblasts and muscle phosphorus MR spectroscopy all failed to reveal a mitochondrial dysfunction. However, muscle biopsies and their mtDNA analysis showed increased mitochondrial biogenesis. Furthermore, patient's fibroblasts grown in the galactose medium were unable to increase ATP content compared with controls, and exhibited abnormally high rate of fusion activity. Genome-wide linkage revealed a locus on chromosome 16q21-q22 with a maximum two-point LOD score of 8.84 for the marker D16S752 and a non-recombinant interval of ～ 6.96 cM. Genomic screening of 45 genes in this interval including several likely candidate genes (CALB2, CYB5B, TK2, DHODH, PLEKHG4) revealed no mutation. Moreover, we excluded the presence of CNVs using array-based comparative genome hybridization. The identification of a new OPA locus (OPA8) in this pedigree demonstrates further genetic heterogeneity in DOA, and our results indicate that the pathogenesis may still involve mitochondria.     

OPA1 (Kjer type) dominant optic atrophy: a novel mitochondrial disease

Dominant optic atrophy (DOA) is the most common form of inherited optic neuropathy. Although heterogeneous, a major locus has been mapped to chromosome 3q28 and the responsible gene, OPA1, was recently identified. OPA1 is a mitochondrial dynamin-related GTPase implicated in the formation and maintenance of the mitochondrial network. To date, 62 mutations have been identified in a total of 201 DOA patients. Most of them (90%) are distributed from exons 8 to 28 with a majority in the GTPase domain (54%). None were found in the alternatively spliced exons 4, 4b, and 5b. Half of them are truncative mutations (50%) with a frequent recurrent allele, c.2708delTTAG. Most missense mutations (81%) cluster within the putative GTPase domain. Various pathogenic mechanisms may play a role in OPA1 DOA. Truncative mutations in the N-terminal region and perhaps missense mutations in the GTPase domain lead to a loss of function of the encoded protein and haplotype insufficiency. However, there is a cluster of truncation mutations in the in C-terminus, a putative dimerization domain, that could act through a dominant negative effect. The findings that OPA1-type DOA, as Leber optic neuropathy, is caused by the impairment of a mitochondrial protein address the question of the vulnerability of the retinal ganglion cell in response to mitochondrial defects.