The Epidemiology of Leber Hereditary Optic Neuropathy in the North East of England

Approaches to the epidemiology of NOHL in the region of Madrid: Survey of neuro-ophthalmologists

OBJECTIVE

To estimate the epidemiology of Leber's optic neuropathy (NOHL) in the Region of Madrid.

MATERIAL AND METHODS

The neuro-ophthalmologists who work at public hospitals of the CAM were interviewed by telephone. They were asked about the number of patients with NOHL that they had diagnosed during the time that they had been responsible for the neuro-ophthalmology department of that public hospital. The time worked and the population attended by the hospital were used to calculate the number of inhabitant-years in follow-up by each center during the corresponding period. The basic information of each case (date of birth, mutation, date of visual loss) was registered to avoid duplications.

RESULTS

Our work estimates a global incidence of 2.34 cases for 10,000,000 inhabitants-year and a prevalence estimated from incidence of one case for each 106.682 inhabitants. This prevalence was very similar in all the studied areas and considerably lower than that reported by other studies.

CONCLUSION

This work constitutes the first approach to the epidemiology of this disease in Spain. The prevalence of LHON in the region of Madrid, is probably lower than that reported in the literature in other regions. The prevalence and the incidence were homogeneously low in the 26 studied areas.

Childhood-Onset Leber Hereditary Optic Neuropathy-Clinical and Prognostic Insights

PURPOSE

To investigate the clinical and molecular genetic features of childhood-onset Leber hereditary optic neuropathy (LHON) to gain a better understanding of the factors influencing the visual outcome in this atypical form of the disease.

DESIGN

Retrospective cohort study.

METHODS

We retrospectively included 2 cohorts of patients with LHON with onset of visual loss before the age of 12 years from Italy and the United Kingdom. Ophthalmologic evaluation, including best-corrected visual acuity, orthoptic evaluation, slit-lamp biomicroscopy, visual field testing, and optical coherence tomography, was considered. Patients were classified based on both the age of onset and the pattern of visual loss.

RESULTS

A total of 68 patients were stratified based on the age of onset of visual loss: group 1 (<3 years): 14 patients (20.6%); group 2 (≥3 to <9 years): 27 patients (39.7%); and group 3 (≥9 to ≤12 years): 27 patients (39.7%). Patients in group 2 achieved a better visual outcome than those in group 3. Patients in groups 1 and 2 had better mean deviation on visual field testing than those in group 3. The mean ganglion cell layer thickness on optical coherence tomography in group 2 was higher than those in groups 1 and 3. Patients were also categorized based on the pattern of visual loss as follows: Subacute Bilateral: 54 patients (66.7%); Insidious Bilateral: 14 patients (17.3%); Unilateral: 9 patients (11.1%); and Subclinical Bilateral: 4 patients (4.9%).

CONCLUSIONS

Children who lose vision from LHON before the age of 9 years have a better visual prognosis than those who become affected in later years, likely representing a "form frustre" of the disease.

Proteomic Profiling Reveals Increased Glycolysis, Decreased Oxidoreductase Activity and Fatty Acid Degradation in Skin Derived Fibroblasts from LHON Patients Bearing m.G11778A

LHON is a common blinding inherited optic neuropathy caused by mutations in mitochondrial genes. In this study, by using skin fibroblasts derived from LHON patients with the most common m.G11778A mutation and healthy objects, we performed proteomic analysis to document changes in molecular proteins, signaling pathways and cellular activities. Furthermore, the results were confirmed by functional studies. A total of 860 differential expression proteins were identified, containing 624 upregulated and 236 downregulated proteins. Bioinformatics analysis revealed increased glycolysis in LHON fibroblasts. A glycolysis stress test showed that ECAR (extra-cellular acidification rate) values increased, indicating an enhanced level of glycolysis in LHON fibroblasts. Downregulated proteins were mainly enriched in oxidoreductase activity. Cellular experiments verified high levels of ROS in LHON fibroblasts, indicating the presence of oxidative damage. KEGG analysis also showed the metabolic disturbance of fatty acid in LHON cells. This study provided a proteomic profile of skin fibroblasts derived from LHON patients bearing m.G11778A. Increased levels of glycolysis, decreased oxidoreductase activity and fatty acid metabolism could represent the in-depth mechanisms of mitochondrial dysfunction mediated by the mutation. The results provided further evidence that LHON fibroblast could be an alternative model for investigating the devastating disease.

Candidate Modifier Genes for the Penetrance of Leber's Hereditary Optic Neuropathy

Leber’s hereditary optic neuropathy (LHON) is a maternally transmitted disease caused by mitochondria DNA (mtDNA) mutation. It is characterized by acute and subacute visual loss predominantly affecting young men. The mtDNA mutation is transmitted to all maternal lineages. However, only approximately 50% of men and 10% of women harboring a pathogenic mtDNA mutation develop optic neuropathy, reflecting both the incomplete penetrance and its unexplained male prevalence, where over 80% of patients are male. Nuclear modifier genes have been presumed to affect the penetrance of LHON. With conventional genetic methods, prior studies have failed to solve the underlying pathogenesis. Whole exome sequencing (WES) is a new molecular technique for sequencing the protein-coding region of all genes in a whole genome. We performed WES from five families with 17 members. These samples were divided into the proband group (probands with acute onset of LHON, n = 7) and control group (carriers including mother and relative carriers with mtDNSA 11778 mutation, without clinical manifestation of LHON, n = 10). Through whole exome analysis, we found that many mitochondria related (MT-related) nuclear genes have high percentage of variants in either the proband group or control group. The MT genes with a difference over 0.3 of mutation percentage between the proband and control groups include AK4, NSUN4, RDH13, COQ3, and FAHD1. In addition, the pathway analysis revealed that these genes were associated with cofactor metabolism pathways. Family-based analysis showed that several candidate MT genes including METAP1D (c.41G > T), ACACB (c.1029del), ME3 (c.972G > C), NIPSNAP3B (c.280G > C, c.476C > G), and NSUN4 (c.4A > G) were involved in the penetrance of LHON. A GWAS (genome wide association study) was performed, which found that ADGRG5 (Chr16:575620A:G), POLE4 (Chr2:7495872T:G), ERMAP (Chr1:4283044A:G), PIGR (Chr1:2069357C:T;2069358G:A), CDC42BPB (Chr14:102949A:G), PROK1 (Chr1:1104562A:G), BCAN (Chr 1:1566582C:T), and NES (Chr1:1566698A:G,1566705T:C, 1566707T:C) may be involved. The incomplete penetrance and male prevalence are still the major unexplained issues in LHON. Through whole exome analysis, we found several MT genes with a high percentage of variants were involved in a family-based analysis. Pathway analysis suggested a difference in the mutation burden of MT genes underlining the biosynthesis and metabolism pathways. In addition, the GWAS analysis also revealed several candidate nuclear modifier genes. The new technology of WES contributes to provide a highly efficient candidate gene screening function in molecular genetics.

Relative Leukocyte Telomere Length and Telomerase Complex Regulatory Markers Association with Leber's Hereditary Optic Neuropathy

Background and Objectives: To evaluate the association of relative leukocyte telomere length (RLTL) and telomerase complex regulatory markers with Leber’s hereditary optic neuropathy (LHON). Material and Methods: A case-control study was performed in patients with LHON (≥18 years) and healthy subjects. The diagnosis of LHON was based on a genetic blood test (next-generation sequencing with Illumina MiSeq, computer analysis: BWA2.1 Illumina BaseSpace, Alamut, and mtDNA Variant analyzer 1000 were performed) and diagnostic criteria approved by the LHON disease protocol. Statistical analysis was performed using the standard statistical software package, IBM SPSS Statistics 27. Statistically significant results were considered when p < 0.05. Results: Significantly longer RLTL was observed in LHON patients than in healthy controls (p < 0.001). RLTL was significantly longer in women and men with LOHN than in healthy women and men in the control group (p < 0.001 and p = 0.003, respectively). In the elderly group (>32 years), RLTL was statistically significantly longer in LHON patients compared with healthy subjects (p < 0.001). The GG genotype of the TERC rs12696304 polymorphism was found to be statistically significantly higher in the LHON group (p = 0.041), and the C allele in the TERC rs12696304 polymorphism was found to be statistically significantly less common in the LHON group (p < 0.001). The RLTL of LHON patients was found to be statistically significantly longer in the TERC rs12696304 polymorphism in all tested genotypes (CC, p = 0.005; CG, p = 0.008; GG, p = 0.025), TEP1 rs1760904 polymorphism in the GA genotype (p < 0.001), and TEP1 gene rs1713418 in the AA and AG genotypes (p = 0.011 and p < 0.001, respectively). Conclusions: The RLTL in LHON patients was found to be longer than in healthy subjects regardless of treatment with idebenone. The TERC rs12696304 polymorphism, of all studied polymorphisms, was the most significantly associated with changes in LHON and telomere length.

Leber Hereditary Optic Neuropathy: Molecular Pathophysiology and Updates on Gene Therapy

Molecular pathophysiology of LHON was reviewed and the current status of gene therapy for LHON is updated.

Pathological mitophagy disrupts mitochondrial homeostasis in Leber's hereditary optic neuropathy

Leber’s hereditary optic neuropathy (LHON), a disease associated with a mitochondrial DNA mutation, is characterized by blindness due to degeneration of retinal ganglion cells (RGCs) and their axons, which form the optic nerve. We show that a sustained pathological autophagy and compartment-specific mitophagy activity affects LHON patient-derived cells and cybrids, as well as induced pluripotent-stem-cell-derived neurons. This is variably counterbalanced by compensatory mitobiogenesis. The aberrant quality control disrupts mitochondrial homeostasis as reflected by defective bioenergetics and excessive reactive oxygen species production, a stress phenotype that ultimately challenges cell viability by increasing the rate of apoptosis. We counteract this pathological mechanism by using autophagy regulators (clozapine and chloroquine) and redox modulators (idebenone), as well as genetically activating mitochondrial biogenesis (PGC1-α overexpression). This study substantially advances our understanding of LHON pathophysiology, providing an integrated paradigm for pathogenesis of mitochondrial diseases and druggable targets for therapy.

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Autophagy and mitophagy are abnormally activated in samples carrying LHON mutations

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Autophagy and mitophagy affect LHON cells’ viability

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Therapeutic approaches targeting autophagy reverts LHON cells’ apoptotic death

Mitochondrial Retinopathies

The retina is an exquisite target for defects of oxidative phosphorylation (OXPHOS) associated with mitochondrial impairment. Retinal involvement occurs in two ways, retinal dystrophy (retinitis pigmentosa) and subacute or chronic optic atrophy, which are the most common clinical entities. Both can present as isolated or virtually exclusive conditions, or as part of more complex, frequently multisystem syndromes. In most cases, mutations of mtDNA have been found in association with mitochondrial retinopathy. The main genetic abnormalities of mtDNA include mutations associated with neurogenic muscle weakness, ataxia and retinitis pigmentosa (NARP) sometimes with earlier onset and increased severity (maternally inherited Leigh syndrome, MILS), single large-scale deletions determining Kearns-Sayre syndrome (KSS, of which retinal dystrophy is a cardinal symptom), and mutations, particularly in mtDNA-encoded ND genes, associated with Leber hereditary optic neuropathy (LHON). However, mutations in nuclear genes can also cause mitochondrial retinopathy, including autosomal recessive phenocopies of LHON, and slowly progressive optic atrophy caused by dominant or, more rarely, recessive, mutations in the fusion/mitochondrial shaping protein OPA1, encoded by a nuclear gene on chromosome 3q29.

Benefit of Stimulus Size V Perimetry for Patients With a Dense Central Scotoma From Leber's Hereditary Optic Neuropathy

Purpose

Leber's hereditary optic neuropathy (LHON) is the most common mtDNA optic neuropathy. It most frequently causes dense bilateral central scotomas that are often characterized in clinical studies by Humphrey visual field testing (HVF) using a stimulus size III. This provides numerical quantification of the visual field defect using the mean deviation. However, this size III testing strategy has limitations. We used stimulus size V to monitor these patients and evaluated intertest variability and dynamic range to determine the testing reliability and reproducibility.

Methods

This was a longitudinal retrospective cohort study comparing Stimulus III and Stimulus V HVF of 62 LHON patients who had reached the plateau stage of the disease. The intertest variability and mean defect were calculated for both stimulus sizes for 38 patients. The mean defect for stimulus size V was calculated using an algorithm developed by the University of Iowa Visual Field Reading Center.

Results

Stimulus size V HVFs had lower inter-test variability as measured by mean defect standard deviation (Z = 169, P < 0.01). The floor effect seen with Stimulus III HVF in LHON, was less pronounced with Stimulus V HVF. The correlation of stimulus size III and V mean defect was strong (r = 0.90, P < 0.01), and a mathematical model was constructed to calculate the Stimulus size V mean defect from the Stimulus size III results (MDstimV = 0.988 x MDStimIII + 1.35, R2 = 0.82 P < 0.01).

Conclusions

Stimulus size V HVF had lower intertest variability and a better dynamic range than Stimulus size III HVF in LHON patients. This makes the stimulus V HVF a more reliable metric to follow LHON patients especially in clinical trials. The mathematical model presented can be used to generate a Stimulus V equivalent mean defect from Stimulus III HVFs.

Translational Relevance

Using Stimulus V HVF in LHON patients increases its ability to detect and quantify a response to treatment, making it a useful metric for future LHON clinical trials and the clinical setting.

Oxidative Stress in Optic Neuropathies

Increasing evidence indicates that changes in the redox system may contribute to the pathogenesis of multiple optic neuropathies. Optic neuropathies are characterized by the neurodegeneration of the inner-most retinal neurons, the retinal ganglion cells (RGCs), and their axons, which form the optic nerve. Often, optic neuropathies are asymptomatic until advanced stages, when visual impairment or blindness is unavoidable despite existing treatments. In this review, we describe systemic and, whenever possible, ocular redox dysregulations observed in patients with glaucoma, ischemic optic neuropathy, optic neuritis, hereditary optic neuropathies (i.e., Leber's hereditary optic neuropathy and autosomal dominant optic atrophy), nutritional and toxic optic neuropathies, and optic disc drusen. We discuss aspects related to anti/oxidative stress biomarkers that need further investigation and features related to study design that should be optimized to generate more valuable and comparable results. Understanding the role of oxidative stress in optic neuropathies can serve to develop therapeutic strategies directed at the redox system to arrest the neurodegenerative processes in the retina and RGCs and ultimately prevent vision loss.

Mutation spectrum of the OPA1 gene in a large cohort of patients with suspected dominant optic atrophy: Identification and classification of 48 novel variants

Autosomal dominant optic atrophy is one of the most common inherited optic neuropathies. This disease is genetically heterogeneous, but most cases are due to pathogenic variants in the OPA1 gene: depending on the population studied, 32–90% of cases harbor pathogenic variants in this gene. The aim of this study was to provide a comprehensive overview of the entire spectrum of likely pathogenic variants in the OPA1 gene in a large cohort of patients. Over a period of 20 years, 755 unrelated probands with a diagnosis of bilateral optic atrophy were referred to our laboratory for molecular genetic investigation. Genetic testing of the OPA1 gene was initially performed by a combined analysis using either single-strand conformation polymorphism or denaturing high performance liquid chromatography followed by Sanger sequencing to validate aberrant bands or melting profiles. The presence of copy number variations was assessed using multiplex ligation-dependent probe amplification. Since 2012, genetic testing was based on next-generation sequencing platforms. Genetic screening of the OPA1 gene revealed putatively pathogenic variants in 278 unrelated probands which represent 36.8% of the entire cohort. A total of 156 unique variants were identified, 78% of which can be considered null alleles. Variant c.2708_2711del/p.(V903Gfs*3) was found to constitute 14% of all disease-causing alleles. Special emphasis was placed on the validation of splice variants either by analyzing cDNA derived from patients´ blood samples or by heterologous splice assays using minigenes. Splicing analysis revealed different aberrant splicing events, including exon skipping, activation of exonic or intronic cryptic splice sites, and the inclusion of pseudoexons. Forty-eight variants that we identified were novel. Nine of them were classified as pathogenic, 34 as likely pathogenic and five as variant of uncertain significance. Our study adds a significant number of novel variants to the mutation spectrum of the OPA1 gene and will thereby facilitate genetic diagnostics of patients with suspected dominant optic atrophy.

From Transcriptomics to Treatment in Inherited Optic Neuropathies

Inherited optic neuropathies, including Leber Hereditary Optic Neuropathy (LHON) and Dominant Optic Atrophy (DOA), are monogenetic diseases with a final common pathway of mitochondrial dysfunction leading to retinal ganglion cell (RGC) death and ultimately loss of vision. They are, therefore, excellent models with which to investigate this ubiquitous disease process-implicated in both common polygenetic ocular diseases (e.g., Glaucoma) and late-onset central nervous system neurodegenerative diseases (e.g., Parkinson disease). In recent years, cellular and animal models of LHON and DOA have matured in parallel with techniques (such as RNA-seq) to determine and analyze the transcriptomes of affected cells. This confluence leaves us at a particularly exciting time with the potential for the identification of novel pathogenic players and therapeutic targets. Here, we present a discussion of the importance of inherited optic neuropathies and how transcriptomic techniques can be exploited in the development of novel mutation-independent, neuroprotective therapies.

Retinal Ganglion Cells-Diversity of Cell Types and Clinical Relevance

Retinal ganglion cells (RGCs) are the bridging neurons that connect the retinal input to the visual processing centres within the central nervous system. There is a remarkable diversity of RGCs and the various subtypes have unique morphological features, distinct functions, and characteristic pathways linking the inner retina to the relevant brain areas. A number of psychophysical and electrophysiological tests have been refined to investigate this large and varied population of RGCs. Technological advances, such as high-resolution optical coherence tomography imaging, have provided additional tools to define the pattern of RGC involvement and the chronological sequence of events in both inherited and acquired optic neuropathies. The mechanistic insights gained from these studies, in particular the selective vulnerability and relative resilience of particular RGC subtypes, are of fundamental importance as they are directly relevant to the development of targeted therapies for these invariably progressive blinding diseases. This review provides a comprehensive description of the various types of RGCs, the developments in proposed methods of classification, and the current gaps in our knowledge of how these RGCs are differentially affected depending on the underlying aetiology. The synthesis of the current body of knowledge on the diversity of RGCs and the pathways that are potentially amenable to therapeutic modulation will hopefully lead to much needed effective treatments for patients with optic neuropathies.

Characteristics of Japanese patients with Leber's hereditary optic neuropathy and idebenone trial: a prospective, interventional, non-comparative study

PURPOSE

Leber's hereditary optic neuropathy (LHON) is a mitochondrial neuropathy that causes acute vision loss. Idebenone, a short-chain ubiquinone analog that preserves mitochondrial function is thought to suppress disease progression in early-onset LHON patients. We investigated the effects of idebenone in Japanese LHON patients.

STUDY DESIGN

Prospective, interventional, non-comparative study in patients with definite LHON diagnosis, under trial registration number UMIN000017939.

METHODS

Fifty-seven patients received 900 mg/day idebenone for 24 weeks. We measured baseline best-corrected visual acuity, visual fields, critical fusion frequency and retinal ganglion cell layer complex thickness; we assessed efficacy at 24 and 48 weeks, and safety throughout.

RESULTS

Patients were predominantly male (91.2%) and most had an mt.11778G>A mutation (94.7%). All patients tolerated idebenone therapy well. Data from the 51 mt.11778 patients were compared with their baseline data. At 48 weeks, significant improvement in best-corrected visual acuity was observed in 17 patients (33.3%). Furthermore, 25.5% of patients showed improvements in visual fields and 33.3% in critical fusion frequency. However, retinal ganglion cell layer complex thickness was significantly reduced. Among patients who started idebenone >1 year after disease onset, visual improvement was found in 12 (38.7%). Among patients who developed LHON before 19 years of age, visual improvement was found in 11 (42.3%).

CONCLUSION

Idebenone's potential and favorable safety profile were confirmed in Japanese LHON patients. However, this study had no placebo group; therefore, we need to undertake a prospective intervention study to further investigate the therapeutic effects of Idebenone in Japanese LHON patients.

Cardiovascular Manifestations of Mitochondrial Disease

Genetic mitochondrial cardiomyopathies are uncommon causes of heart failure that may not be seen by most physicians. However, the prevalence of mitochondrial DNA mutations and somatic mutations affecting mitochondrial function are more common than previously thought. In this review, the pathogenesis of genetic mitochondrial disorders causing cardiovascular disease is reviewed. Treatment options are presently limited to mostly symptomatic support, but preclinical research is starting to reveal novel approaches that may lead to better and more targeted therapies in the future. With better understanding and clinician education, we hope to improve clinician recognition and diagnosis of these rare disorders in order to improve ongoing care of patients with these diseases and advance research towards discovering new therapeutic strategies to help treat these diseases.

Juvenile open-angle Glaucoma associated with Leber's hereditary optic neuropathy: a case report and literature review

BACKGROUND

Leber's hereditary optic neuropathy (LHON) is a maternally inherited recessive disease rarely complicated with glaucoma. We conducted a clinical and genetic retrospective case series to describe three cases of juvenile open-angle glaucoma (JOAG) and an ND4 m11778G > A mitochondrial DNA (mtDNA) mutation, which is pathognomonic for LHON.

CASE PRESENTATION

Patient 1 was a 16-year-old boy diagnosed with bilateral JOAG and high myopia. His intraocular pressure (IOP) was poorly controlled with the use of full topical anti-glaucoma medications. His best-corrected visual acuity (BCVA) decreased gradually over 5 years. Fundoscopic examination revealed bilateral enlarged disc cupping of the optic nerves with sectorial excavation and reduction of the neural rim in the left eye. His visual field (VF) was characterized by bilateral progressive central scotoma. Pattern visual evoked potentials (VEPs) and pattern electroretinograms (ERGs) showed extinguished responses in both eyes. Because of the non-specific visual field findings and the optic neuropathy disclosed by the pattern VEPs and pattern ERGs, we arranged a genetic test for the patient, which revealed an m11778G > A mtDNA mutation. Patient 2, the younger brother of Patient 1, was a 15-year-old boy who had been diagnosed with bilateral JOAG in 2010. The BCVA of both eyes remained at 1.0 during the follow-up period. Fundoscopic examination revealed bilateral mildly paled optic disc with enlarged cupping and reduction of the neural rim. The pattern ERG revealed a decreased N95 amplitude bilaterally. The genetic test revealed an m11778G > A mtDNA mutation. Patient 3 was a 35-year-old man with bilateral JOAG. His BCVA decreased gradually over 10 years. Fundoscopic examination revealed paled optic disc with enlarged disc cupping and reduction of the neural rim in both eyes. The pattern ERG revealed a decreased N95 amplitude bilaterally. The genetic test revealed an m11778G > A mtDNA mutation.

CONCLUSIONS

This case series describes three patients with concomitant occurrence of JOAG and LHON. These two diseases may have a cumulative effect on oxidative stress and retinal ganglion cell death with the rapid deterioration of vision, which may occur during adolescence.