A recurrent deletion mutation in OPA1 causes autosomal dominant optic atrophy in a Chinese family.
ABSTRACT: 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.
Project description:BACKGROUND:Autosomal-dominant optic atrophy (ADOA) is one of the most common types of inherited optic atrophy. We identify OPA1 pathogenic variants and assess the clinical features of a cohort of Chinese ADOA patients Materials and Methods: Detailed clinical evaluations were performed and genomic DNA was extracted from peripheral blood for all the participants. Sanger sequencing was used to analyze all exons and exon/intron junctions of OPA1 for eight pedigrees. Target exome capture plus next-generation sequencing (NGS) were applied for one atypical family with photophobia. Reverse transcription polymerase chain reaction was carried out to further characterize the mRNA change of selected splicing alteration. RESULTS:All 17 patients had impaired vision and optic-disk pallor; however, the clinical severity varied markedly. Two patients complicated with hearing loss. Six novel and two reported pathogenic variants in OPA1 (GenBank Accession No. NM_130837.2) were identified including four nonsynonymous variants (c.2400T > G, c.1468T > C, c.1567A > G and c.1466T > C), two splicing variants (c.2984-1_2986delGAGA and c.2983 + 5G > A), one small deletion (c.2960_2968delGCGTTCAAC), and one small insertion (c.3009_3010insA). RNA analysis revealed the splicing variant c.2984-1_2986delGAGA caused small deletion of mRNA (r.2983_2988del). CONCLUSIONS:ADOA patients presented variable clinical manifestations. Novel OPA1 pathogenic variants are the main genetic defect for Chinese ADOA cases. NGS may be a useful molecular testing tool for atypical ADOA.
Project description:PurposeAutosomal-dominant optic atrophy (ADOA), often associated with mutations in the OPA1 gene (chromosome 3q28-q29) is rarely reported in Asia. Our aim was to identify and describe this condition in an Asian population in Singapore.Patients and methodsPreliminary cross-sectional study at the Singapore National Eye Centre, including patients with clinical suspicion of ADOA, who subsequently underwent genetic testing by direct sequencing of the OPA1 gene.ResultsAmong 12 patients (10 families) with clinically suspected ADOA, 7 patients (5 families) from 3 different ethnic origins (Chinese, Indian, and Malay) carried a heterozygous pathogenic variant in the OPA1 gene. The OPA1 mutations were located on exons 8, 9, 11, and 17: c.869G>A (p.Arg290Glu), c.892A>G (p.Ser298Gly), c.1140G>A (splicing mutation), and c.1669C>T (p.Arg557*), respectively. One splicing mutation (c.871-1G>A) was identified in intron 8. We also identified a novel mutation causing optic atrophy and deafness (c.892A>G (p.Ser298Gly)). Among the phenotypic features, colour pupillometry disclosed a dissociation between low vision and preserved pupillary light reflex in ADOA.ConclusionWe report the first cases of genetically confirmed OPA1-related ADOA from Singapore, including a novel mutation causing 'ADOA plus' syndrome. Further epidemiological studies are needed in order to determine the prevalence of ADOA in South-East Asia.
Project description: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.
Project description: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. METHODS: To define the relationships between OPA1 mutations and mtDNA backgrounds, we determined the haplogroup affiliation of 41 French patients affected by OPA1-related ADOA by control-region sequencing and RFLP survey of their mtDNAs. RESULTS: The comparison between patient and reference populations did not revealed any significant difference. CONCLUSION: Our results argue against a strong influence of mtDNA background on ADOA expression. These data allow to conclude that OPA1 could be considered as a "severe mutation", directly responsible of the optic atrophy, whereas OPA1-negative ADOA and LHON mutations need an external factor(s) to express the pathology (i.e. synergistic interaction with mitochondrial background).
Project description:PURPOSE: Autosomal dominant optic atrophy (ADOA, OMIM 165500), an inherited optic neuropathy that leads to retinal ganglion cell degeneration and reduced visual acuity during the early decades of life, is mainly associated with mutations in the OPA1 gene. Here we report a novel ADOA phenotype associated with a new pathogenic OPA1 gene mutation. METHODS: The patient, a 62-year-old woman, was referred for acute, painless, and severe visual loss in her right eye. Acute visual loss in her left eye occurred a year after initial presentation. MRI confirmed the diagnosis of isolated atrophic bilateral optic neuropathy. We performed DNA sequencing of the entire coding sequence and the exon/intron junctions of the OPA1 gene, and we searched for the mitochondrial DNA mutations responsible for Leber hereditary optic atrophy by sequencing entirely mitochondrial DNA. Mitochondrial respiratory chain complex activity and mitochondrial morphology were investigated in skin fibroblasts from the patient and controls. RESULTS: We identified a novel heterozygous missense mutation (c.2794C>T) in exon 27 of the OPA1 gene, resulting in an amino acid change (p.R932C) in the protein. This mutation, which affects a highly conserved amino acids, has not been previously reported, and was absent in 400 control chromosomes. Mitochondrial DNA sequence analysis did not reveal any mutation associated with Leber hereditary optic neuropathy or any pathogenic mutations. The investigation of skin fibroblasts from the patient revealed a coupling defect of oxidative phosphorylation and a larger proportion of short mitochondria than in controls. CONCLUSIONS: The presence of an OPA1 mutation indicates that this sporadic, late-onset acute case of optic neuropathy is related to ADOA and to a mitochondrial energetic defect. This suggests that the mutational screening of the OPA1 gene would be justified in atypical cases of optic nerve atrophy with no evident cause.
Project description:PURPOSE: Autosomal dominant optic atrophy (ADOA) is the most common form of hereditary optic neuropathy caused by mutations in the optic atrophy 1 (OPA1) gene. It is characterized by insidious onset with a selective degeneration of retinal ganglion cells, variable loss of visual acuity, temporal optic nerve pallor, tritanopia, and development of central, paracentral, or cecocentral scotomas. Here we describe the clinical and molecular findings in a large Italian family with ADOA. METHODS: Routine ophthalmologic examination and direct sequencing of all coding regions of the OPA1 gene were performed. Further characterization of a new OPA1 gene insertion was performed by reverse transcription-PCR (RT-PCR) of RNA from patients and control subjects. RESULTS: We identified an Alu-element insertion located in intron 7 of OPA1 causing an in-frame deletion of exon 8 in 18 family members. CONCLUSIONS: The predicted consequence of this mutation is the loss of the guanosine triphosphatase (GTPase) activity of OPA1. Alu insertions have been reported in the literature as causing human genetic disease. However, this is the first report of a pathogenic OPA1 gene mutation resulting from an Alu insertion.
Project description: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. METHODS: Forty unrelated ADOA patients, selected from a group of 100 ADOA patients as being negative for OPA1 point mutations, were tested for genomic rearrangements in OPA1 by multiplex ligation probe amplification (MLPA). When only one probe was abnormal results were confirmed by additional manually added probes. Segregation analysis was performed in families with detected mutations when possible. RESULTS: Ten families had OPA1 deletions, including two with deletions of the entire coding region and eight with intragenic deletions. Segregation analysis was possible in five families, and showed that the deletions segregated with the disease. CONCLUSION: Deletions in the OPA1 gene were found in 10 patients presenting with phenotypic autosomal dominant optic neuropathy. Genetic testing for deletions in OPA1 should be offered for patients with clinically diagnosed ADOA and no OPA1 mutations detected by DNA sequencing analysis.
Project description:Autosomal dominant optic atrophy (ADOA), a form of progressive bilateral blindness due to loss of retinal ganglion cells and optic nerve deterioration, arises predominantly from mutations in the nuclear gene for the mitochondrial GTPase, OPA1. OPA1 localizes to mitochondrial cristae in the inner membrane where electron transport chain complexes are enriched. While OPA1 has been characterized for its role in mitochondrial cristae structure and organelle fusion, possible effects of OPA1 on mitochondrial function have not been determined.Mitochondria from six ADOA patients bearing OPA1 mutations and ten ADOA patients with unidentified gene mutations were studied for respiratory capacity and electron transport complex function. Results suggest that the nuclear DNA mutations that give rise to ADOA in our patient population do not alter mitochondrial electron transport.We conclude that the pathophysiology of ADOA likely stems from the role of OPA1 in mitochondrial structure or fusion and not from OPA1 support of oxidative phosphorylation.
Project description:Autosomal Dominant Optic Atrophy (ADOA) is the most common inherited optic atrophy where vision impairment results from specific loss of retinal ganglion cells of the optic nerve. Around 60% of ADOA cases are linked to mutations in the OPA1 gene. OPA1 is a fission-fusion protein involved in mitochondrial inner membrane remodelling. ADOA presents with marked variation in clinical phenotype and varying degrees of vision loss, even among siblings carrying identical mutations in OPA1. To determine whether the degree of vision loss is associated with the level of mitochondrial impairment, we examined mitochondrial function in lymphoblast cell lines obtained from six large Australian OPA1-linked ADOA pedigrees. Comparing patients with severe vision loss (visual acuity [VA]<6/36) and patients with relatively preserved vision (VA>6/9) a clear defect in mitochondrial ATP synthesis and reduced respiration rates were observed in patients with poor vision. In addition, oxidative phosphorylation (OXPHOS) enzymology in ADOA patients with normal vision revealed increased complex II+III activity and levels of complex IV protein. These data suggest that OPA1 deficiency impairs OXPHOS efficiency, but compensation through increases in the distal complexes of the respiratory chain may preserve mitochondrial ATP production in patients who maintain normal vision. Identification of genetic variants that enable this response may provide novel therapeutic insights into OXPHOS compensation for preventing vision loss in optic neuropathies.
Project description:PURPOSE: To describe the genotype-phenotype correlation in four Greek pedigrees with autosomal dominant optic atrophy (ADOA) and OPA1 mutations. METHODS: Seven patients from four unrelated families (F1, F2, F3, F4) were clinically assessed for visual acuity, color vision, ptosis, afferent pupillary defects, and visual fields and underwent orthoptic assessment, slit-lamp biomicroscopy, and fundus examination to establish their clinical status. Genomic DNA was extracted from peripheral blood samples from all participants. The coding region (exons 1-28), including the intron-exon boundaries of the OPA1 gene, was screened in the probands of the four families, as well as in seven additional family members (four affected and three unaffected) with PCR and direct DNA sequencing. RESULTS: All patients presented bilateral decrease in best-corrected visual acuity and temporal pallor of the optic disc. The visual fields of the adult patients showed characteristic scotomata. Other signs were present in some patients such as decreased color discrimination and a gray crescent within the neuroretinal rim. After the OPA1 gene was sequenced, a previously undescribed heterozygous splice-site mutation c.784-1G>T in intron 7 was detected in family F2. In families F1, F3, and F4, a previously reported in-frame deletion c.876_878delTGT/p.(Val294del), the frameshift c.2366delA/p.(Asn789Metfs*11), and splice-site c.1140+5G>C mutations were detected, respectively. CONCLUSIONS: This is the first report of molecular characterization of Greek patients with ADOA. Our findings provide additional information regarding the genotype-phenotype correlation and establish the role of the OPA1 gene in Greek patients with ADOA.