Inherited mitochondrial optic neuropathies

MSC-mediated mitochondrial transfer restores mitochondrial DNA and function in neural progenitor cells of Leber's hereditary optic neuropathy

Leber's hereditary optic neuropathy (LHON) is a debilitating mitochondrial disease associated with mutations in mitochondrial DNA (mtDNA). Unfortunately, the available treatment options for LHON patients are limited due to challenges in mitochondrial replacement. In our study, we reprogramming LHON urine cells into induced pluripotent stem cells (iPSCs) and differentiating them into neural progenitor cells (NPCs) and neurons for disease modeling. Our research revealed that LHON neurons exhibited significantly higher levels of mtDNA mutations and reduced mitochondrial function, confirming the disease phenotype. However, through co-culturing LHON iPSC-derived NPCs with mesenchymal stem cells (MSCs), we observed a remarkable rescue of mutant mtDNA and a significant improvement in mitochondrial metabolic function in LHON neurons. These findings suggest that co-culturing with MSCs can enhance mitochondrial function in LHON NPCs, even after their differentiation into neurons. This discovery holds promise as a potential therapeutic strategy for LHON patients.

Quantifying the effects of the mitochondrial genome on milk production traits in dairy cows: empirical results and modelling challenges

Significant advances in livestock traits have been achieved primarily through selection strategies targeting variation in the nuclear genome, with little attention given to mitogenome variation. We analyzed the influence of the mitogenome on milk production traits of Holstein cattle in Croatia based on strategically generated next-generation sequencing data for 109 cows pedigree-linked to 7115 milk production records (milk, fat and protein yield) from 3006 cows (first 5 lactations). Since little is known about the biology of the relationship between mitogenome variation and production traits, our quantitative genetic modeling was complex. Thus, the proportion of total variance explained by mitogenome inheritance was estimated using 5 different models: (1) cytoplasmic model with maternal lineages (CYTO), (2) haplotypic model with mitogenome sequences (HAPLO), (3) amino acid model with unique amino acid sequences (AMINO), (4) evolutionary model based on a phylogenetic analysis using Bayesian Evolutionary Analysis Sampling Trees phylogenetic analysis (EVOL), and (5) mitogenome SNP model (SNPmt). The polygenic autosomal and X chromosome additive genetic effects based on pedigree were modeled, together with the effects of herd-year-season interaction, permanent environment, location, and age at first calving. The estimated proportions of phenotypic variance explained by mitogenome in 4 different models (CYTO, HAPLO, AMINO, and SNPmt) were found to be substantial given the size of mitogenome, ranging from 5% to 7% for all 3 milk traits. At the same time, a negligible proportion of the phenotypic variance was explained by mitogenome with the EVOL model. Similarly, in all models, no proportion of phenotypic variance was explained by the X chromosome. Although our results should be confirmed in other dairy cattle populations, including a large number of sequenced mitogenomes and nuclear genomes, the potential of utilizing mitogenome information in animal breeding is promising, especially as the acquisition of complete genome sequences becomes cost-effective.

Ganglion Cell Complex Thickness and Visual Function in Chronic Leber Hereditary Optic Neuropathy

Purpose

To evaluate the correlation between the macular ganglion cell complex (GCC) thickness measured with manually corrected segmentation and visual function in individuals with chronic Leber hereditary optic neuropathy (LHON).

Methods

Twenty-six chronic LHON subjects (60% treated with idebenone or Q10) from the Swedish LHON registry were enrolled. Best-corrected visual acuity (BCVA), visual field tests, and optical coherence tomography (OCT) were performed. Visual field was evaluated with the Haag-Streit Octopus 900 with the Esterman test and a custom 30° test. Canon OCT-HS100 scans were exported to the Iowa Reference Algorithm. GCC thickness was obtained after the segmentation was corrected manually in nine macular sectors.

Results

The GCC thickness was overestimated by 16 to 30 µm in different macular sectors with the automated segmentation compared with the corrected (P < 0.001). GCC thickness in all sectors showed significant correlation with all functional parameters. The strongest correlation was seen for the external temporal sector (BCVA: r = 0.604, P < 0.001; mean defect: r = 0.457, P = 0.001; Esterman score: r = 0.421, P = 0.003). No differences were seen between treated and untreated subjects with regard to GCC and visual field scores (P > 0.05), but BCVA was better among treated subjects (P = 0.017).

Conclusions

The corrected GCC thickness showed correlation with visual function in chronic LHON subjects. The frequently occurring segmentation errors in OCT measurements related to chronic LHON can potentially be misleading in monitoring of disease progression and in evaluating the treatment effects. Precise measurements of GCC could serve as a sensitive tool to monitor structural changes in LHON. We therefore emphasize the importance of careful evaluation of the accuracy of OCT segmentation.

Fetal and obstetrics manifestations of mitochondrial diseases

During embryonic and neonatal development, mitochondria have essential effects on metabolic and energetic regulation, shaping cell fate decisions and leading to significant short- and long-term effects on embryonic and offspring health. Therefore, perturbation on mitochondrial function can have a pathological effect on pregnancy. Several shreds of evidence collected in preclinical models revealed that severe mitochondrial dysfunction is incompatible with life or leads to critical developmental defects, highlighting the importance of correct mitochondrial function during embryo-fetal development. The mechanism impairing the correct development is unknown and may include a dysfunctional metabolic switch in differentiating cells due to decreased ATP production or altered apoptotic signalling. Given the central role of mitochondria in embryonic and fetal development, the mitochondrial dysfunction typical of Mitochondrial Diseases (MDs) should, in principle, be detectable during pregnancy. However, little is known about the clinical manifestations of MDs in embryonic and fetal development. In this manuscript, we review preclinical and clinical evidence suggesting that MDs may affect fetal development and highlight the fetal and maternal outcomes that may provide a wake-up call for targeted genetic diagnosis.

Cascade testing in mitochondrial diseases: a cross-sectional retrospective study

BACKGROUND

Cascade testing can offer improved surveillance and timely introduction of clinical management for the at-risk biological relatives. Data on cascade testing and costs in mitochondrial diseases are lacking. To address this gap, we performed a cross-sectional retrospective study to provide a framework for cascade testing in mitochondrial diseases, to estimate the eligibility versus real-time uptake of cascade testing and to evaluate the cost of the genetic diagnosis of index cases and the cost of predictive cascade testing.

METHODS

Data was collected through retrospective chart review. The variant inheritance pattern guided the identification of eligible first-degree relatives: (i) Males with mitochondrial DNA (mtDNA) single nucleotide variants (SNVs) - siblings and mothers. (ii) Females with mtDNA SNVs - siblings, mothers and offspring. (iii) Autosomal Dominant (AD) nuclear DNA (nDNA) variants - siblings, offspring and both parents. (iv) Autosomal Recessive (AR) nDNA variants - siblings.

RESULTS

We recruited 99 participants from the Adult Mitochondrial Disease Clinic in Sydney. The uptake of cascade testing was 55.2% in the mtDNA group, 55.8% in the AD nDNA group and 0% in AR nDNA group. Of the relatives in mtDNA group who underwent cascade testing, 65.4% were symptomatic, 20.5% were oligosymptomatic and 14.1% were asymptomatic. The mean cost of cascade testing for eligible first-degree relatives (mtDNA group: $694.7; AD nDNA group: $899.1) was lower than the corresponding index case (mtDNA group: $4578.4; AD nDNA group: $5715.1) (p < 0.001).

CONCLUSION

The demand for cascade testing in mitochondrial diseases varies according to the genotype and inheritance pattern. The real-time uptake of cascade testing can be influenced by multiple factors. Early diagnosis of at-risk biological relatives of index cases through cascade testing, confirms the diagnosis in those who are symptomatic and facilitates implementation of surveillance strategies and clinical care at an early stage of the disease.

Inhibition of angiogenesis by the secretome from iPSC-derived retinal ganglion cells with Leber's hereditary optic neuropathy-like phenotypes

The blood supply in the retina ensures photoreceptor function and maintains regular vision. Leber's hereditary optic neuropathy (LHON), caused by the mitochondrial DNA mutations that deteriorate complex I activity, is characterized by progressive vision loss. Although some reports indicated retinal vasculature abnormalities as one of the comorbidities in LHON, the paracrine influence of LHON-affected retinal ganglion cells (RGCs) on vascular endothelial cell physiology remains unclear. To address this, we established an in vitro model of mitochondrial complex I deficiency using induced pluripotent stem cell-derived RGCs (iPSC-RGCs) treated with a mitochondrial complex I inhibitor rotenone (Rot) to recapitulate LHON pathologies. The secretomes from Rot-treated iPSC-RGCs (Rot-iPSC-RGCs) were collected, and their treatment effect on human umbilical vein endothelial cells (HUVECs) was studied. Rot induced LHON-like characteristics in iPSC-RGCs, including decreased mitochondrial complex I activity and membrane potential, and increased mitochondrial reactive oxygen species (ROS) and apoptosis, leading to mitochondrial dysfunction. When HUVECs were exposed to conditioned media (CM) from Rot-iPSC-RGCs, the angiogenesis of HUVECs was suppressed compared to those treated with CM from control iPSC-RGCs (Ctrl-iPSC-RGCs). Angiogenesis-related proteins were altered in the secretomes from Rot-iPSC-RGC-derived CM, particularly angiopoietin, MMP-9, uPA, collagen XVIII, and VEGF were reduced. Notably, GeneMANIA analysis indicated that VEGFA emerged as the pivotal angiogenesis-related protein among the identified proteins secreted by health iPSC-RGCs but reduced in the secretomes from Rot-iPSC-RGCs. Quantitative real-time PCR and western blots confirmed the reduction of VEGFA at both transcription and translation levels, respectively. Our study reveals that Rot-iPSC-RGCs establish a microenvironment to diminish the angiogenic potential of vascular cells nearby, shedding light on the paracrine regulation of LHON-affected RGCs on retinal vasculature.

Leber hereditary optic neuropathy in Slovenia: quality of life and costs from patient perspective

INTRODUCTION

Leber hereditary optic neuropathy (LHON) is the most commonly diagnosed mitochondrial disorder, resulting in colour vision abnormalities and rapid but painless deterioration of central vision. While numerous studies have assessed the impact of LHON on the quality of life (QoL) of LHON patients, the financial impact of the disease remains unexplored. This study attempts to calculate both the direct non-medical costs and the indirect costs associated with productivity losses experienced by people with LHON and their unpaid caregivers in Slovenia, in addition to assessing their QoL. Due to the rarity of the disease, the study involved a small sample size, which is important to note for interpreting the results.

METHODS

The analysis was conducted on nine adult participants diagnosed with LHON, representing one-third of the total number of known Slovenian patients with this condition. To thoroughly assess the economic and social impact of LHON, tailored questionnaires were designed to collect information on demographics, socioeconomic status, LHON severity, and associated non-medical and indirect costs.

RESULTS

The mean age of the study participants was 48.8 years (SD 13.3; n = 9). The annual productivity loss attributable to LHON, taking both absenteeism and relative presenteeism into account, was calculated to be EUR 11,608 per person affected. The mean VFQ-25 score, a measure of vision-related quality of life, for adult LHON patients was 30.4 (SD 12.9).

CONCLUSION

The findings highlight the significant economic and social burden of LHON on patients and their families. Ensuring prompt, accurate diagnosis, access to treatment, financial support, and psychological counselling and services are critical to helping individuals cope with and mitigate the profound challenges of vision loss and living with LHON.

Impaired mitochondrial morphological plasticity and failure of mitophagy associated with the G11778A mutation of LHON

Mitochondrial dynamics were examined in human dermal fibroblasts biopsied from a confirmed Leber's Hereditary Optic Neuropathy (LHON) patient with a homoplasmic G11778A mutation of the mitochondrial genome. Expression of the G11778A mutation did not impart any discernible difference in mitochondrial network morphology using widefield fluorescence microscopy. However, at the ultrastructural level, cells expressing this mutation exhibited an impairment of mitochondrial morphological plasticity when forced to utilize oxidative phosphorylation (OXPHOS) by transition to glucose-free, galactose-containing media. LHON fibroblasts also displayed a transient increase in mitophagy upon transition to galactose media. These results provide new insights into the consequences of the G11778A mutation of LHON and the pathological mechanisms underlying this disease.

The discovery of a ten-generation m.C1494T pedigree in the east of England with probable links to King Richard III

This paper reports the discovery of a m.C1494T pedigree in the east of England made during a search for matrilineal relations of King Richard III. The mitochondrial DNA variant m.C1494T has been associated with aminoglycoside-induced deafness. This variant is very uncommon. although pedigrees with this variant have previously been found in China and Spain. The members of the newly identified pedigree all belong to the mitochondrial haplogroup J1c2c3, which is also the haplogroup of King Richard III. The presence of a few people in the USA from the same haplogroup has previously been noted, and it is now known that one of the people can show his descent from a couple who lived in Nottinghamshire, England, in the late 1700's. The mitochondrial DNA sequence of this man, at present living in the USA, and of his 4th cousin, twice removed, living in Lincoln, England, has shown they belong to haplogroup J1c2c3 and both have the variant m.C1494T; thereby, allowing the production of a multi-generational pedigree originating in the east of England. Fortunately, deafness has not been found in any living member of this large pedigree. It was also noted that the link to the family of King Richard III has not been firmly defined; however the circumstantial evidence is strong as many of his family members lived in this part of England.

Peripheral blood mononuclear cell respiratory function is associated with progressive glaucomatous vision loss

Intraocular pressure (IOP) is currently the only modifiable risk factor for glaucoma and all licensed treatments lower IOP. However, many patients continue to lose vision despite IOP-lowering treatment. Identifying biomarkers for progressive vision loss would have considerable clinical utility. We demonstrate that lower peripheral blood mononuclear cell (PBMC) oxygen consumption rate (OCR) is strongly associated with faster visual field (VF) progression in patients treated by lowering IOP (P < 0.001, 229 eyes of 139 participants), explaining 13% of variance in the rate of progression. In a separate reference cohort of untreated patients with glaucoma (213 eyes of 213 participants), IOP explained 16% of VF progression variance. OCR is lower in patients with glaucoma (n = 168) than in controls (n = 50; P < 0.001) and is lower in patients with low baseline IOP (n = 99) than those with high baseline IOP (n = 69; P < 0.01). PBMC nicotinamide adenine dinucleotide (NAD) levels are lower in patients with glaucoma (n = 29) compared to controls (n = 25; P < 0.001) and strongly associated with OCR (P < 0.001). Our results support PBMC OCR and NAD levels as new biomarkers for progressive glaucoma.

Mitochondrial retinopathies and optic neuropathies: The impact of retinal imaging on modern understanding of pathogenesis, diagnosis, and management

Advancements in ocular imaging have significantly broadened our comprehension of mitochondrial retinopathies and optic neuropathies by examining the structural and pathological aspects of the retina and optic nerve in these conditions. This article aims to review the prominent imaging characteristics associated with mitochondrial retinopathies and optic neuropathies, aiming to deepen our insight into their pathogenesis and clinical features. Preceding this exploration, the article provides a detailed overview of the crucial genetic and clinical features, which is essential for the proper interpretation of in vivo imaging. More importantly, we will provide a critical analysis on how these imaging modalities could serve as biomarkers for characterization and monitoring, as well as in guiding treatment decisions. However, these imaging methods have limitations, which will be discussed along with potential strategies to mitigate them. Lastly, the article will emphasize the potential advantages and future integration of imaging techniques in evaluating patients with mitochondrial eye disorders, considering the prospects of emerging gene therapies.

Leber hereditary optic neuropathy in Czechia and Slovakia: Quality of life and costs from patient perspective

Introduction

Leber hereditary optic neuropathy (LHON) is the most frequent mitochondrial disease causing dyschromatopsia and progressive central visual loss that is subacute in progression and painless. Several studies have been published assessing QoL in patients with LHON, but no estimate of the economic burden has been reported to date. This study aims to quantify direct non-medical and indirect costs (productivity loss) incurred by LHON patients and their informal caregivers in Czechia and Slovakia, as well as to assess their quality of life.

Methods

The study was performed in 27 adults and children with LHON. To determine the socioeconomic burden of LHON, separate questionnaires for adults, children, and their parents were developed, including demographic and socioeconomic data. The following data were collected: age, education, family size, severity of LHON, non-medical direct and indirect costs of LHON.

Results

The mean age of adult respondents was 36.1 years (SD 13.1; n = 21). The total cost of absenteeism was EUR 1003 per person/year in adult employees, and EUR 2711 per person/year in children's parents. The productivity loss as a consequence of LHON due to combined relative absenteeism and relative presenteeism was estimated at EUR 9840 per an adult patient/year, and EUR 6298 per a parent/year, respectively. The mean cost of informal care was estimated at EUR 4502 (SD 4772; n = 6) per person/year. The mean VFQ-25 score for adult patients with LHON was 43.47 (SD 15.86).

Conclusion

The results of this study clearly show that patients with LHON and their families face an extensive socioeconomic burden related to this rare disease. Early, timely and appropriate access to diagnosis, treatment, and reimbursement decisions, but also to psychological counselling and services may help the patients and their relatives adapt and cope with the challenging aspects of vision loss and life with the disease.

Galactose-replacement unmasks the biochemical consequences of the G11778A mitochondrial DNA mutation of LHON in patient-derived fibroblasts

Leber's hereditary optic neuropathy (LHON) is a visual impairment associated with mutations of mitochondrial genes encoding elements of the electron transport chain. While much is known about the genetics of LHON, the cellular pathophysiology leading to retinal ganglion cell degeneration and subsequent vision loss is poorly understood. The impacts of the G11778A mutation of LHON on bioenergetics, redox balance and cell proliferation were examined in patient-derived fibroblasts. Replacement of glucose with galactose in the culture media reveals a deficit in the proliferation of G11778A fibroblasts, imparts a reduction in ATP biosynthesis, and a reduction in capacity to accommodate exogenous oxidative stress. While steady-state ROS levels were unaffected by the LHON mutation, cell survival was diminished in response to exogenous H2O2.

Deep Brain Stimulation for Medication Refractory Tremor in Leber Optic Neuropathy Plus Syndrome

Leber hereditary optic neuropathy (LHON) is a mitochondrial disorder that presents with acute to subacute onset of unilateral progressive optic neuropathy, with sequential involvement of the fellow eye months to years later. The condition may be accompanied by neurological symptoms, including tremors, dystonia, seizures, or psychosis, in which case, it is termed LHON-plus. Here, we present the case of a 53-year-old man who was initially diagnosed with essential tremor but was later found to have LHON-plus after the onset of bilateral visual loss and a genetic panel. His essential tremor was refractory to standard pharmacological therapies, including propranolol, primidone, and topiramate. As a result, he elected to undergo bilateral deep brain stimulation (DBS) of the bilateral ventral intermediate nucleus of the thalamus with a dramatic improvement in symptoms. To our knowledge, this is the first case of essential tremor presenting in the context of LHON-plus to be treated successfully with DBS. While DBS has been applied in LHON-plus presenting with dystonia with limited success, our outcome suggests that there is promise in this approach and that more research is needed to evaluate it.

Elamipretide Topical Ophthalmic Solution for the Treatment of Subjects with Leber Hereditary Optic Neuropathy: A Randomized Trial

PURPOSE

This study aimed to assess the safety, tolerability, and potential efficacy of topical elamipretide in patients affected with Leber hereditary optic neuropathy (LHON).

DESIGN

This phase II, prospective, randomized, vehicle-controlled, single-center clinical trial involved administration of elamipretide 1% topical ophthalmic solution to patients with LHON over a 52-week double-masked treatment period, followed by an open-label extension (OLE) for up to 108 additional weeks of treatment.

PARTICIPANTS

Twelve patients with LHON were included in this study. Patients aged 18 to 50 years with decreased vision for at least ≥ 1 year and ≤ 10 years, and a genetically confirmed diagnosis of m.11778G>A LHON were eligible for this trial.

METHODS

For the first 52 weeks of the study, patients were randomized to 1 of 3 groups: elamipretide in both eyes or elamipretide in 1 eye (left eye and right eye were considered separate groups) and vehicle in the other eye, followed by an OLE in which both eyes were treated with elamipretide.

MAIN OUTCOME MEASURES

The primary outcome measure was assessment of adverse events (AEs) from the administration of topical elamipretide, and the primary efficacy end point was change in best-corrected visual acuity (BCVA). Secondary outcome measures included changes in color vision, visual field mean deviation, and electrophysiological outcomes.

RESULTS

Elamipretide was well tolerated with the majority of AEs being mild to moderate and resolving spontaneously. The change from baseline in BCVA in elamipretide-treated eyes was not significantly different from the vehicle eyes at any time point. Six of 12 subjects met the criteria for clinically relevant benefit (CRB). In the post hoc analysis, change from baseline in mean deviation in the central visual field was significantly greater in elamipretide-treated eyes versus the vehicle eyes. Compared with baseline, both treatment groups showed improvement in color discrimination and contrast sensitivity in the OLE.

CONCLUSIONS

Elamipretide treatment was generally well tolerated, with no serious AEs reported. Although this study did not meet its primary BCVA efficacy end point, improvements across assessments on visual function during the OLE and the post hoc findings of the Humphrey automated visual field central region were encouraging and require further exploration.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Therapeutic benefit of idebenone in patients with Leber hereditary optic neuropathy: The LEROS nonrandomized controlled trial

Leber hereditary optic neuropathy (LHON) is a mitochondrial disease leading to rapid and severe bilateral vision loss. Idebenone has been shown to be effective in stabilizing and restoring vision in patients treated within 1 year of onset of vision loss. The open-label, international, multicenter, natural history-controlled LEROS study (ClinicalTrials.gov NCT02774005) assesses the efficacy and safety of idebenone treatment (900 mg/day) in patients with LHON up to 5 years after symptom onset (N = 199) and over a treatment period of 24 months, compared to an external natural history control cohort (N = 372), matched by time since symptom onset. LEROS meets its primary endpoint and confirms the long-term efficacy of idebenone in the subacute/dynamic and chronic phases; the treatment effect varies depending on disease phase and the causative mtDNA mutation. The findings of the LEROS study will help guide the clinical management of patients with LHON.

Peripapillary retinal nerve fibre layer thinning, perfusion changes and optic neuropathy in carriers of Leber hereditary optic neuropathy-associated mitochondrial variants

BACKGROUND

We investigated Leber hereditary optic neuropathy (LHON) families for variation in peripapillary retinal nerve fibre layer thickness and perfusion, and associated optic nerve dysfunction.

METHOD

A group of LHON-affected patients (n=12) and their asymptomatic maternal relatives (n=16) underwent examination including visual acuity (VA), visual-evoked-potential and optic nerve imaging including optical coherence tomography (OCT) and OCT angiography of the peripapillary retinal nerve fibre layer (RNFL). A control sample was also examined (n=10). The software imageJ was used to measure perfusion by assessing vessel density (VD), and statistical software 'R' was used to analyse data.

RESULTS

The LHON-affected group (n=12) had significantly reduced peripapillary VD (median 7.9%, p=0.046). Overall, the LHON asymptomatic relatives (n=16) had no significant change in peripapillary VD (p=0.166), though three eyes had VD which fell below the derived normal range at 6% each, with variable VA from normal to blindness; LogMAR median 0, range 0-2.4. In contrast, RNFL thickness was significantly reduced in the LHON-affected group (median 51 µm, p=0.003), and in asymptomatic relatives (median 90 µm, p=0.01), compared with controls (median 101 µm). RNFL thinning had greater specificity compared with reduced perfusion for optic nerve dysfunction in asymptomatic carriers (92% vs 66%).

CONCLUSION

Overall, reduced peripapillary retinal nerve fibre layer perfusion was observed in those affected by LHON but was not reduced in their asymptomatic relatives, unlike RNFL thinning which was significantly reduced in both groups versus controls. The presence of RNFL changes was associated with signs of optic neuropathy in asymptomatic relatives.

Genetic variants affecting NQO1 protein levels impact the efficacy of idebenone treatment in Leber hereditary optic neuropathy

Idebenone, the only approved treatment for Leber hereditary optic neuropathy (LHON), promotes recovery of visual function in up to 50% of patients, but we can neither predict nor understand the non-responders. Idebenone is reduced by the cytosolic NAD(P)H oxidoreductase I (NQO1) and directly shuttles electrons to respiratory complex III, bypassing complex I affected in LHON. We show here that two polymorphic variants drastically reduce NQO1 protein levels when homozygous or compound heterozygous. This hampers idebenone reduction. In its oxidized form, idebenone inhibits complex I, decreasing respiratory function in cells. By retrospectively analyzing a large cohort of idebenone-treated LHON patients, classified by their response to therapy, we show that patients with homozygous or compound heterozygous NQO1 variants have the poorest therapy response, particularly if carrying the m.3460G>A/MT-ND1 LHON mutation. These results suggest consideration of patient NQO1 genotype and mitochondrial DNA mutation in the context of idebenone therapy.

The human OPA1delTTAG mutation induces adult onset and progressive auditory neuropathy in mice

Dominant optic atrophy (DOA) is one of the most prevalent forms of hereditary optic neuropathies and is mainly caused by heterozygous variants in OPA1, encoding a mitochondrial dynamin-related large GTPase. The clinical spectrum of DOA has been extended to a wide variety of syndromic presentations, called DOAplus, including deafness as the main secondary symptom associated to vision impairment. To date, the pathophysiological mechanisms underlying the deafness in DOA remain unknown. To gain insights into the process leading to hearing impairment, we have analyzed the Opa1delTTAG mouse model that recapitulates the DOAplus syndrome through complementary approaches combining morpho-physiology, biochemistry, and cellular and molecular biology. We found that Opa1delTTAG mutation leads an adult-onset progressive auditory neuropathy in mice, as attested by the auditory brainstem response threshold shift over time. However, the mutant mice harbored larger otoacoustic emissions in comparison to wild-type littermates, whereas the endocochlear potential, which is a proxy for the functional state of the stria vascularis, was comparable between both genotypes. Ultrastructural examination of the mutant mice revealed a selective loss of sensory inner hair cells, together with a progressive degeneration of the axons and myelin sheaths of the afferent terminals of the spiral ganglion neurons, supporting an auditory neuropathy spectrum disorder (ANSD). Molecular assessment of cochlea demonstrated a reduction of Opa1 mRNA level by greater than 40%, supporting haploinsufficiency as the disease mechanism. In addition, we evidenced an early increase in Sirtuin 3 level and in Beclin1 activity, and subsequently an age-related mtDNA depletion, increased oxidative stress, mitophagy as well as an impaired autophagic flux. Together, these results support a novel role for OPA1 in the maintenance of inner hair cells and auditory neural structures, addressing new challenges for the exploration and treatment of OPA1-linked ANSD in patients.

Progress in diagnosis and treatment of Leber's hereditary optic neuropathy

Leber's hereditary optic neuropathy (LHON) is a mitochondrial genetic disease with central vision loss as the main symptom. It is one of the diseases that cause vision loss and optic atrophy in young and middle-aged people. The mutations of these three primary mitochondrial mutations, m.11778G>A, m.14484T>C, and m.3460G>A, are the main molecular basis, but their pathogenesis is also affected by nuclear genes, mitochondrial genetic background, and environmental factors. This article summarizes the research progress on molecular pathogenesis, clinical symptoms, and treatment of LHON in recent years, aiming to summarize the genetic pathogenesis and clinical treatment points of LHON.

Mitochondrially Targeted Gene Therapy Rescues Visual Loss in a Mouse Model of Leber's Hereditary Optic Neuropathy

Leber's hereditary optic neuropathy (LHON) is a common mitochondrial genetic disease, causing irreversible blindness in young individuals. Current treatments are inadequate, and there is no definitive cure. This study evaluates the effectiveness of delivering wildtype human NADH ubiquinone oxidoreductase subunit 4 (hND4) gene using mito-targeted AAV(MTSAAV) to rescue LHOH mice. We observed a declining pattern in electroretinograms amplitudes as mice aged across all groups (p < 0.001), with significant differences among groups (p = 0.023; Control vs. LHON, p = 0.008; Control vs. Rescue, p = 0.228). Inner retinal thickness and intraocular pressure did not change significantly with age or groups. Compared to LHON mice, those rescued with wildtype hND4 exhibited improved retinal visual acuity (0.29 ± 0.1 cy/deg vs. 0.15 ± 0.1 cy/deg) and increased functional hyperemia response (effect of flicker, p < 0.001, effect of Group, p = 0.004; Interaction Flicker × Group, p < 0.001). Postmortem analysis shows a marked reduction in retinal ganglion cell density in the LHON group compared to the other groups (Effect of Group, p < 0.001, Control vs. LHON, p < 0.001, Control vs. Rescue, p = 0.106). These results suggest that MTSAAV-delivered wildtype hND4 gene rescues, at least in part, visual impairment in an LHON mouse model and has the therapeutic potential to treat this disease.

The diagnostic accuracy of photopic negative responses evoked by broadband and chromatic stimuli in a clinically heterogeneous population

PURPOSE

To compare the diagnostic accuracy of the photopic negative response (PhNR) elicited by red-blue (RB) and white-white (WW) stimuli, for detection of retinal ganglion cell (RGC) dysfunction in a heterogeneous clinical cohort.

METHODS

Adults referred for electrophysiological investigations were recruited consecutively for this single-centre, prospective, paired diagnostic accuracy study. PhNRs were recorded to red flashes (1.5 cd·s·m-2) on a blue background (10 cd·m-2) and to white flashes on a white background (the latter being the ISCEV standard LA 3 stimulus). PhNR results were compared with a reference test battery assessing RGC/optic nerve structure and function including optical coherence tomography (OCT) retinal nerve fibre layer thickness and mean RGC volume measurements, fundus photography, pattern electroretinography and visual evoked potentials. Primary outcome measures were differences in sensitivity and specificity of the two PhNR methods.

RESULTS

Two hundred and forty-three participants were initially enrolled, with 200 (median age 54; range 18-95; female 65%) meeting inclusion criteria. Sensitivity was 53% (95% confidence intervals [CI] 39% to 68%) and 62% (95% CI 48% to 76%), for WW and RB PhNRs, respectively. Specificity was 80% (95% CI 74% to 86%) and 78% (95% CI 72% to 85%), respectively. There was a statistically significant difference between sensitivities (p = 0.046) but not specificities (p = 0.08) of the two methods. Receiver operator characteristic (ROC) area under the curve (AUC) values were 0.73 for WW and 0.74 for RB PhNRs.

CONCLUSION

PhNRs to red flashes on a blue background may be more sensitive than white-on-white stimuli, but there is no significant difference between specificities. This study highlights the value and potential convenience of using white-on-white stimuli, already used widely for routine ERG assessment.

Leber Hereditary Optic Neuropathy (LHON) in Patients with Presumed Childhood Monocular Amblyopia

BACKGROUND

Most Leber hereditary optic neuropathy (LHON) cases are bilateral and sequential; however, there are rare unilateral examples, or those in which the delay of onset of vision loss between one and the other eye is longer. In the case of presumed childhood amblyopia in one eye, vision loss in the good eye may be the only symptom of bilateral disease, which was unnoticed in the previously amblyopic eye, or a preexisting episode of LHON in the "amblyopic" eye. The clinical decision in such cases may be difficult and suggestive of other forms of atypical optic neuropathy until confirmed by genetic testing.

CASE SERIES

We present three genetically confirmed (MT-ND1:m.3700G>A, MT-ND6:m14484 T>C, and MT-ND4:m.11778G>A) patients with subacute vision loss in the previously good eye, with the other eye believed to be amblyopic from childhood and their features different from what would be expected in true amblyopia. In all, electrophysiology testing showed a bilaterally reduced amplitude of PERG with low VEP P100 wave amplitudes and prolonged peak time in both eyes, also unusual for amblyopia. During follow-up, the pallor of the optic discs progressed in all eyes. Significant thinning of the peripapillary retinal nerve fiber layer (pRNFL; retinal nerve fiber layer around the optic disc) and ganglion cell complex (GCC) in the macular region was present. All three patients had a peculiar history. The first patient was treated for presumed hyperopic amblyopia that did not improve since childhood, experienced visual loss in the good eye at the age of 17, and was negative for the three typical LHON mutations. Extended testing confirmed an atypical pathogenic variant MT-ND1:m.3700G>A in homoplasmy. The second patient with presumed strabismic amblyopia had an unusual presentation of vision loss only at the age of 61, and after the exclusion of other causes, a typical MT-ND4:m.11778G>A pathogenic variant was found in homoplasmy. The third case was peculiar as he had presumed strabismic amblyopia since childhood and had some degree of disc pallor in the amblyopic eye upon presenting with loss of vision in the good eye at the age of 21, and a typical pathogenic variant m14484 T>C, p.Met64Val was subsequently confirmed. However, one year after disease onset, he started to experience significant spontaneous functional improvement in the non-amblyopic up to 1.0 Snellen whilst improvement in the presumed amblyopic eye was modest, suggesting preexisting amblyopia. This interestingly extensive improvement was carefully followed by electrophysiology as well as visual acuity and fields.

CONCLUSIONS

This report shows three different scenarios of presentation of LHON in patients with presumed uniocular amblyopia from childhood. In such cases, the diagnosis may be difficult, and detailed structural and functional evaluation of the optic nerve head is necessary to assess whether an earlier LHON episode was misdiagnosed as amblyopia or whether LHON presented bilaterally on both eyes whilst only being noticed in the previously good eye.

Optical coherence tomography angiography in neuro-ophthalmology

PURPOSE OF REVIEW

Optical coherence tomography angiography (OCTA) is a novel, noninvasive imaging technique, which provides depth resolved visualization of microvasculature of the retina and choroid. Although OCTA has been widely used for the evaluation of a number of retinal diseases, its use in the field of neuro-ophthalmology has been less studied. In this review, we provide an update on the utility of OCTA in neuro-ophthalmic conditions.

RECENT FINDINGS

Peripapillary and macular microvasculature analyses have indicated that OCTA can be a promising tool for early detection of a number of neuro-ophthalmic diseases, differential diagnosis, and monitoring of disease progression. Recent studies have demonstrated that structural and functional impairment can develop at early stages in some conditions such as in multiple sclerosis and Alzheimer's disease even in the absence of overt clinical symptoms. Furthermore, this dye-less technique can be a valuable adjunct tool in the detection of complications commonly seen in some congenital entities such optic disc drusen.

SUMMARY

Since its introduction, OCTA has emerged as an important imaging approach shedding light on unrevealed pathophysiological mechanisms of several ocular diseases. The use of OCTA as a biomarker in the field of neuro-ophthalmology has recently gained considerable attention with studies supporting its role in clinical setting while larger studies are warranted for correlating these findings with traditional diagnostic procedures and clinical features and outcomes.

Mitochondrial DNA variants in a cohort from Argentina with suspected Leber's hereditary optic neuropathy (LHON)

The present study investigates the spectrum and analysis of mitochondrial DNA (mtDNA) variants associated with Leber hereditary optic neuropathy (LHON) in an Argentinean cohort, analyzing 3 LHON-associated mitochondrial genes. In 32% of the cases, molecular confirmation of the diagnosis could be established, due to the identification of disease-causing variants. A total of 54 variants were observed in a cohort of 100 patients tested with direct sequencing analysis. The frequent causative mutations m.11778G>A in MT-ND4, m.3460G>A in MT-ND1, and m.14484T>C in MT-ND6 were identified in 28% of the cases of our cohort. Secondary mutations in this Argentinean LHON cohort were m.11253T>C p.Ile165Thr in MT-ND4, identified in three patients (3/100, 3%) and m.3395A>G p.Tyr30Cys in MT-ND1, in one of the patients studied (1%). This study shows, for the first time, the analysis of mtDNA variants in patients with a probable diagnosis of LHON in Argentina. Standard molecular methods are an effective first approach in order to achieve genetic diagnosis of the disease, leaving NGS tests for those patients with negative results.

Indirect Comparison of Lenadogene Nolparvovec Gene Therapy Versus Natural History in Patients with Leber Hereditary Optic Neuropathy Carrying the m.11778G>A MT-ND4 Mutation

INTRODUCTION

Lenadogene nolparvovec is a promising novel gene therapy for patients with Leber hereditary optic neuropathy (LHON) carrying the m.11778G>A ND4 mutation (MT-ND4). A previous pooled analysis of phase 3 studies showed an improvement in visual acuity of patients injected with lenadogene nolparvovec compared to natural history. Here, we report updated results by incorporating data from the latest phase 3 trial REFLECT in the pool, increasing the number of treated patients from 76 to 174.

METHODS

The visual acuity of 174 MT-ND4-carrying patients with LHON injected in one or both eyes with lenadogene nolparvovec from four pooled phase 3 studies (REVERSE, RESCUE and their long-term extension trial RESTORE; and REFLECT trial) was compared to the spontaneous evolution of an external control group of 208 matched patients from 11 natural history studies.

RESULTS

Treated patients showed a clinically relevant and sustained improvement in their visual acuity when compared to natural history. Mean improvement versus natural history was - 0.30 logMAR (+ 15 ETDRS letters equivalent) at last observation (P < 0.01) with a maximal follow-up of 3.9 years after injection. Most treated eyes were on-chart as compared to less than half of natural history eyes at 48 months after vision loss (89.6% versus 48.1%; P < 0.01) and at last observation (76.1% versus 44.4%; P < 0.01). When we adjusted for covariates of interest (gender, age of onset, ethnicity, and duration of follow-up), the estimated mean gain was - 0.43 logMAR (+ 21.5 ETDRS letters equivalent) versus natural history at last observation (P < 0.0001). Treatment effect was consistent across all phase 3 clinical trials. Analyses from REFLECT suggest a larger treatment effect in patients receiving bilateral injection compared to unilateral injection.

CONCLUSION

The efficacy of lenadogene nolparvovec in improving visual acuity in MT-ND4 LHON was confirmed in a large cohort of patients, compared to the spontaneous natural history decline. Bilateral injection of gene therapy may offer added benefits over unilateral injection.

TRIAL REGISTRATION NUMBERS

NCT02652780 (REVERSE); NCT02652767 (RESCUE); NCT03406104 (RESTORE); NCT03293524 (REFLECT); NCT03295071 (REALITY).

Leber's hereditary optic neuropathy: Update on current diagnosis and treatment

Leber's hereditary optic neuropathy (LHON) is a fairly prevalent mitochondrial disorder (1:50,000) arising from the dysfunction of the mitochondrial respiratory chain, which eventually leads to apoptosis of retinal ganglion cells. The usual presentation is that of a young male with a sequential reduction in visual acuity. OCT has been used to study the pattern of optic nerve involvement in LHON, showing early thickening of the inferior and superior retinal nerve fibre layer and ganglion cell layer thinning corresponding with the onset of symptoms. Of the three primary mutations for LHON, the m.14484T>C mutation has the best visual prognosis. Recent emerging therapeutic options for LHON include idebenone and the introduction of genetic vector therapy, which is currently in phase III clinical trials. Screening of family members and adequate advice to avoid environmental triggers, such as smoking and alcohol consumption, are also cornerstones in the management of LHON.

Study design and baseline characteristics for the reflect gene therapy trial ofm.11778g>A/ND4-LHON

Objective

REFLECT is the first randomised, double-masked, placebo-controlled multicentre phase 3 clinical trial that evaluated the efficacy and safety of bilateral intravitreal (IVT) injection of lenadogene nolparvovec in subjects with Leber hereditary optic neuropathy carrying the m.11778G>A mutation.

Methods and analysis

A total of 98 subjects were enrolled with vision loss of ≤12 months. The subjects were randomised to one of two treatment arms with all subjects receiving an intravitreal (IVT) injection of lenadogene nolparvovec in their first affected eye and the second-affected eye randomised to receive IVT of either lenadogene nolparvovec or placebo.

Results

The majority of subjects were male with a mean duration of vision loss of 8.3 months. All but one subject experienced bilateral loss of vision at the time of injection. The mean best-corrected visual acuity of first-affected eyes was worse compared with second/not-yet-affected eyes. Analysis of retinal anatomical parameters showed increased thinning in the first-affected eyes when compared with the second/not-yet-affected eyes with both treatment arms showing significant changes compared with unaffected individuals.

Conclusion

The REFLECT trial is the third and the largest phase 3 clinical study evaluating lenadogene nolparvovec in m.11778G>A Leber hereditary optic neuropathy (LHON) subjects. The observed demographics in REFLECT are consistent with previous reports in LHON subjects in the acute and dynamic phases of LHON disease. Combined with the visual function and anatomical parameters obtained in the previous RESCUE and REVERSE trials, REFLECT has provided a uniformly collected data set that should help direct future LHON clinical trials.

Drug Discovery Strategies for Inherited Retinal Degenerations

Inherited retinal degeneration is a group of blinding disorders afflicting more than 1 in 4000 worldwide. These disorders frequently cause the death of photoreceptor cells or retinal ganglion cells. In a subset of these disorders, photoreceptor cell death is a secondary consequence of retinal pigment epithelial cell dysfunction or degeneration. This manuscript reviews current efforts in identifying targets and developing small molecule-based therapies for these devastating neuronal degenerations, for which no cures exist. Photoreceptors and retinal ganglion cells are metabolically demanding owing to their unique structures and functional properties. Modulations of metabolic pathways, which are disrupted in most inherited retinal degenerations, serve as promising therapeutic strategies. In monogenic disorders, great insights were previously obtained regarding targets associated with the defective pathways, including phototransduction, visual cycle, and mitophagy. In addition to these target-based drug discoveries, we will discuss how phenotypic screening can be harnessed to discover beneficial molecules without prior knowledge of their mechanisms of action. Because of major anatomical and biological differences, it has frequently been challenging to model human inherited retinal degeneration conditions using small animals such as rodents. Recent advances in stem cell-based techniques are opening new avenues to obtain pure populations of human retinal ganglion cells and retinal organoids with photoreceptor cells. We will discuss concurrent ideas of utilizing stem-cell-based disease models for drug discovery and preclinical development.

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.

Mitochondrial Genome Alterations, Cytochrome C Oxidase Activity, and Oxidative Stress: Implications in Primary Open-angle Glaucoma

Aim

To evaluate mitochondrial genome alterations, cytochrome c oxidase (COX) activity, and oxidative stress in primary open-angle glaucoma (POAG).

Methodology

Whole mitochondrial genome was screened in 75 POAG cases and 105 controls by polymerase chain reaction (PCR) sequencing. COX activity was measured from peripheral blood mononuclear cells (PBMCs). A protein modeling study was done to evaluate the impact of G222E variant on protein function. Levels of 8-hydroxy-2-deoxyguanosine (8-OHdG), 8-isoprostane (8-IP), and total antioxidant capacity (TAC) were also measured.

Results

A total of 156 and 79 mitochondrial nucleotide variations were found in the cohort of 75 POAG patients and 105 controls, respectively. Ninety-four (60.26%) variations spanned the coding region, and 62 (39.74%) variations spanned noncoding regions (D-loop, 12SrRNA, and 16SrRNA) of mitochondrial genome in POAG patients. Out of 94 nucleotide changes in coding region, 68 (72.34%) were synonymous changes, 23 (24.46%) non-synonymous, and three (3.19%) were found in the region coding for transfer ribonucleic acid (tRNA). Three changes (p.E192K in ND1, p.L128Q in ND2, and p.G222E in COX2) were found to be pathogenic. Twenty-four (32.0%) patients were positive for either of these pathogenic mitochondrial deoxyribonucleic acid (mtDNA) nucleotide changes. Majority of cases (18.7%) had pathogenic mutation in COX2 gene. Patients who harbored pathogenic mtDNA change in COX2 gene had significantly lower levels of COX activity (p < 0.0001) and TAC (p = 0.004), and higher levels of 8-IP (p = 0.01) as compared to patients who did not harbor this mtDNA. G222E changed the electrostatic potential and adversely impacted protein function of COX2 by affecting nonpolar interactions with neighboring subunits.

Conclusion

Pathogenic mtDNA mutations were present in POAG patients, which were associated with reduced COX activity and increased levels of oxidative stress.

Clinical significance

POAG patients should be evaluated for mitochondrial mutations and oxidative stress and may be managed accordingly with antioxidant therapies.

How to cite this article

Mohanty K, Mishra S, Dada R, et al. Mitochondrial Genome Alterations, Cytochrome C Oxidase Activity, and Oxidative Stress: Implications in Primary Open-angle Glaucoma. J Curr Glaucoma Pract 2022;16(3):158-165.

Abnormal morphology and function in retinal ganglion cells derived from patients-specific iPSCs generated from individuals with Leber's hereditary optic neuropathy

Leber's hereditary optic neuropathy (LHON) is a maternally inherited eye disease that results from degeneration of retinal ganglion cells (RGC). Mitochondrial ND4 11778G > A mutation, which affects structural components of complex I, is the most prevalent LHON-associated mitochondrial DNA (mtDNA) mutation worldwide. The m.11778G > A mutation is the primary contributor underlying the development of LHON and X-linked PRICKLE3 allele (c.157C > T, p.Arg53Trp) linked to biogenesis of ATPase interacts with m.11778G > A mutation to cause LHON. However, the lack of appropriate cell and animal models of LHON has been significant obstacles for deep elucidation of disease pathophysiology, specifically the tissue-specific effects. Using RGC-like cells differentiated from induced pluripotent stem cells (iPSCs) from members of one Chinese family (asymptomatic subjects carrying only m.11778G > A mutation or PRICKLE3 p.Arg53Trp mutation, symptomatic individuals bearing both m.11778G > A and PRICKLE3 p.Arg53Trp mutations and control lacking these mutations), we demonstrated the deleterious effects of mitochondrial dysfunctions on the morphology and functions of RGCs. Notably, iPSCs bearing only m.11778G > A or p.Arg53Trp mutation exhibited mild defects in differentiation to RGC-like cells. The RGC-like cells carrying only m.11778G > A or p.Arg53Trp mutation displayed mild defects in RGC morphology, including the area of soma and numbers of neurites, electrophysiological properties, ATP contents and apoptosis. Strikingly, those RGC-like cells derived from symptomatic individuals harboring both m.11778G > A and p.Arg53Trp mutations displayed greater defects in the development, morphology and functions than those in cells bearing single mutation. These findings provide new insights into pathophysiology of LHON arising from RGC deficiencies caused by synergy between m.11778G > A and PRICKLE3 p.Arg53Trp mutation.

The Genetics of Ethambutol-Induced Optic Neuropathy: A Narrative Review

Tuberculosis (TB) is a global health problem with the major brunt of disease occurring in developing countries. The cornerstone of treatment of TB is anti-tubercular therapy (ATT), which includes rifampicin, isoniazid, pyrazinamide and ethambutol. Because of emerging drug resistance, treatment failures, defaulters and increasing incidence of disseminated and extrapulmonary TB, the guidelines have been modified in some countries. Ethambutol is prescribed for longer times (in some cases >8 months) and hence the incidence of ethambutol-induced optic neuropathy (EtON) is expected to rise. The fundamental question which needs explanation is why only a small subset of patients on ethambutol are prone to develop loss of vision. This review focuses on available genetic studies which provide evidence that mitochondria are the likely substrates involved in the final pathway of reactive oxidative damage of the papillo-macular bundle. Genetic analysis of mitochondrial mutations encoding genes involved in oxidative phosphorylation pathways may help in isolating the subset of patients who are genetically susceptible. If the groups having high risk of developing EtON are recognised then prolonged duration of ethambutol treatment can be avoided in these susceptible individuals. A better understanding of the pathophysiology will also pave the way for the development of management strategies in this condition.

From Bench to Bedside-Delivering Gene Therapy for Leber Hereditary Optic Neuropathy

Leber hereditary optic neuropathy (LHON) is a rare, maternally inherited mitochondrial disorder that presents with severe bilateral sequential vision loss, due to the selective degeneration of retinal ganglion cells (RGCs). Since the mitochondrial genetic basis for LHON was uncovered in 1988, considerable progress has been made in understanding the pathogenetic mechanisms driving RGC loss, which has enabled the development of therapeutic approaches aimed at mitigating the underlying mitochondrial dysfunction. In this review, we explore the genetics of LHON, from bench to bedside, focusing on the pathogenetic mechanisms and how these have informed the development of different gene therapy approaches, in particular the technique of allotopic expression with adeno-associated viral vectors. Finally, we provide an overview of the recent gene therapy clinical trials and consider the unanswered questions, challenges, and future prospects.

Multi-mtDNA Variants May Be a Factor Contributing to Mitochondrial Function Variety in the Skin-Derived Fibroblasts of Leber's Hereditary Optic Neuropathy Patients

Heterogeneity is a major feature of Leber's hereditary optic neuropathy (LHON) and has a significant impact on the manifestation and diagnosis of the disease. This study explored whether multiple variations in mitochondrial genes were associated with the heterogeneity, mainly phenotypic heterogeneity. Ophthalmic examinations were conducted in two probands with LHON with G11778A and multiple mitochondrial DNA gene (mtDNA) variants. Skin fibroblast cell lines were generated from patients and age- and sex-matched controls. ROS levels, mitochondrial membrane potential, cell energy respiration, and metabolic functions were measured. Flow cytometry and cell viability tests were performed to evaluate the cell apoptosis levels and fate. We found that cells with more mtDNA variants had higher ROS levels, lower mitochondrial membrane potential, and weaker respiratory function. Flow cytometry and cell viability testing showed that multiple mtDNA variants are associated with different levels of cell viability and apoptosis. In conclusion, we found that skin-derived fibroblast cells from G11778A LHON patients could be used as models for LHON research. Multi-mtDNA variants contribute to mitochondrial function variety, which may be associated with heterogeneity in patients with LHON.

Varying Clinical Phenotypes of Mitochondrial DNA T12811C Mutation: A Case Series Report

The T12811C mitochondrial DNA (mtDNA) mutation has been reported in Leber hereditary optic neuropathy (LHON) previously, with vision loss as the main manifestation. The involvement of other organ systems, including the central and peripheral nervous system, heart, and extraocular muscles, has not been well described. This case series report investigated four patients with T12811C mtDNA mutation, verified through a next generation sequencing. Two male patients presented with bilateral subacute visual decrease combined with involvement of multiple organ systems: leukoencephalopathy, hypertrophic cardiomyopathy, neurosensory deafness, spinal cord lesion and peripheral neuropathies. Two female patients presented with progressive ptosis and ophthalmoplegia, one of whom also manifested optic atrophy. This study found out that patients harboring T12811C mtDNA mutation manifested not only as vision loss, but also as a multi-system disorder affecting the nervous system, heart, and extraocular muscles.

Characterisation of a novel OPA1 splice variant resulting in cryptic splice site activation and mitochondrial dysfunction

Autosomal dominant optic atrophy (DOA) is an inherited optic neuropathy that results in progressive, bilateral visual acuity loss and field defects. OPA1 is the causative gene in around 60% of cases of DOA. The majority of patients have a pure ocular phenotype, but 20% have extra-ocular features (DOA +). We report on a patient with DOA + manifesting as bilateral optic atrophy, spastic paraparesis, urinary incontinence and white matter changes in the central nervous system associated with a novel heterozygous splice variant NM_015560.2(OPA1):c.2356-1 G > T. Further characterisation, which was performed using fibroblasts obtained from a skin biopsy, demonstrated that this variant altered mRNA splicing of the OPA1 transcript, specifically a 21 base pair deletion at the start of exon 24, NM_015560.2(OPA1):p.Cys786_Lys792del. The majority of variant transcripts were shown to escape nonsense-mediated decay and modelling of the predicted protein structure suggests that the in-frame 7 amino acid deletion may affect OPA1 oligomerisation. Fibroblasts carrying the c.2356-1 G > T variant demonstrated impaired mitochondrial bioenergetics, membrane potential, increased cell death, and disrupted and fragmented mitochondrial networks in comparison to WT cells. This study suggests that the c.2356-1 G > T OPA1 splice site variant leads to a cryptic splice site activation and may manifest in a dominant-negative manner, which could account for the patient's severe syndromic phenotype.

Analysis of the entire mitochondrial genome reveals Leber's hereditary optic neuropathy mitochondrial DNA mutations in an Arab cohort with multiple sclerosis

Several mitochondrial DNA (mtDNA) mutations of Leber's hereditary optic neuropathy (LHON) have been reported in patients with multiple sclerosis (MS) from different ethnicities. To further study the involvement of LHON mtDNA mutations in MS in the Arab population, we analyzed sequencing data of the entire mitochondrial genome from 47 unrelated Saudi individuals, 23 patients with relapse-remitting MS (RRMS) and 24 healthy controls. Ten LHON mutations/variants were detected in the patients but were absent in the controls. Of them, the common primary pathogenic mutation m.14484T>C and the rare mutation m.10237T>C were found in one patient, whereas the rare mutation m.9101T>C was found in another patient. The remaining were secondary single nucleotide variants (SNVs) found either in synergy with the primary/rare mutations or individually in other patients. Patients carrying LHON variants also exhibited distinct mtDNA variants throughout the mitochondrial genome, eight were previously reported in patients with LHON. Moreover, five other LHON-related SNVs differed significantly in their prevalence among patients and controls (P < 0.05). This study, the first to investigate LHON mtDNA mutations/variants in a Saudi cohort may suggest a role of these mutations/variants in the pathogenesis or genetic predisposition to MS, a possibility which needs to be explored further in a large-scale.

Clinical Overview of Leber Hereditary Optic Neuropathy

Leber hereditary ptic neuropathy (LHON) is a disease of young adults with bilateral, painless, subacute visual loss. The peak age of onset of LHON is in the second and third decades of life. Men are 4 times more likely to be affected than women. In about 25-50% of cases, both eyes are affected simultaneously. In unilateral cases, the other eye is usually affected 2 to 3 months later. Visual acuity deteriorates to counting fingers or worse with a dense central or centrocecal scotoma. In the subacute phase, the optic disc may appear hyperemic with swelling of the peripapillary retinal nerve fibre layer, peripapillary telangiectasias, and increased vascular tortuosity. Ocular coherence tomography of the macula shows marked thinning of the ganglion cell complex even at this stage. The diagnosis of LHON is made in a subject with a consistent clinical history and/or one of three common pathogenic mitochondrial DNA (mtDNA) variants identified by molecular genetic testing. Idebenone was approved by the European Medicines Agency under exceptional circumstances for the treatment of LHON. Current evidence suggests some benefit to vision in a subset of affected individuals treated with idebenone, particularly when treated within the first year of onset of vision loss. In this article, we discuss aetiology, clinical features, diagnosis, differential dignosis, prognosis and treatment.

Demographics and etiologic characteristics of non-glaucomatous optic atrophy: a single-center cross-sectional study from Turkey

BACKGROUND

Optic atrophy is an end-stage pathology of optic nerve diseases that is characterized by optic nerve pallor and vision loss. Because of its sight-threatening effects, understanding its epidemiology and etiology is crucial. In this study, we aimed to determine the epidemiologic features of optic nerve pathologies which lead to optic atrophy.

METHODS

This is a cross-sectional study in which, medical records of optic atrophy patients who were followed up in our clinic between 1999 and 2020 were evaluated. Three hundred and sixty eyes of 226 patients were included in the study. Demographic data were received from the patients' files. Patients with glaucomatous optic atrophy, consecutive optic atrophy and patients with less than a year follow-up were excluded from the study.

RESULTS

The most frequent reason of optic atrophy was central nervous system diseases (27.43%) followed by secondary non-arteritic ischemic optic neuropathy (26.99%). The most frequent etiology of optic atrophy was non-arteritic ischemic optic neuropathy in males and central nerve system-related pathologies in females. The highest presentation age (mean 63.6 ± 17.85 years) was observed in arteritic ischemic optic neuropathy and central nerve system-related optic atrophy had the lowest presentation age (median 14 years, IQR [34]).

CONCLUSION

Central nerve system diseases and non-arteritic ischemic optic neuropathies were the most common causes of non-glaucomatous and non-consecutive optic atrophy in Turkey. Better understanding of underlying etiologies of optic atrophy may lead us to take precautions timely for irreversible optic nerve dysfunction which is an important reason of blindness.

Clinical and genetic spectrums of 413 North African families with inherited retinal dystrophies and optic neuropathies

Background

Inherited retinal dystrophies (IRD) and optic neuropathies (ION) are the two major causes world-wide of early visual impairment, frequently leading to legal blindness. These two groups of pathologies are highly heterogeneous and require combined clinical and molecular diagnoses to be securely identified. Exact epidemiological studies are lacking in North Africa, and genetic studies of IRD and ION individuals are often limited to case reports or to some families that migrated to the rest of the world. In order to improve the knowledge of their clinical and genetic spectrums in North Africa, we reviewed published data, to illustrate the most prevalent pathologies, genes and mutations encountered in this geographical region, extending from Morocco to Egypt, comprising 200 million inhabitants.

Main body

We compiled data from 413 families with IRD or ION together with their available molecular diagnosis. The proportion of IRD represents 82.8% of index cases, while ION accounted for 17.8%. Non-syndromic IRD were more frequent than syndromic ones, with photoreceptor alterations being the main cause of non-syndromic IRD, represented by retinitis pigmentosa, Leber congenital amaurosis, and cone-rod dystrophies, while ciliopathies constitute the major part of syndromic-IRD, in which the Usher and Bardet Biedl syndromes occupy 41.2% and 31.1%, respectively. We identified 71 ION families, 84.5% with a syndromic presentation, while surprisingly, non-syndromic ION are scarcely reported, with only 11 families with autosomal recessive optic atrophies related to OPA7 and OPA10 variants, or with the mitochondrial related Leber ION. Overall, consanguinity is a major cause of these diseases within North African countries, as 76.1% of IRD and 78.8% of ION investigated families were consanguineous, explaining the high rate of autosomal recessive inheritance pattern compared to the dominant one. In addition, we identified many founder mutations in small endogamous communities.

Short conclusion

As both IRD and ION diseases constitute a real public health burden, their under-diagnosis in North Africa due to the absence of physicians trained to the identification of inherited ophthalmologic presentations, together with the scarcity of tools for the molecular diagnosis represent major political, economic and health challenges for the future, to first establish accurate clinical diagnoses and then treat patients with the emergent therapies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02340-7.

Brain Gray Matter Atrophy and Functional Connectivity Remodeling in Patients With Chronic LHON

Purpose

The aim of this study was to investigate the brain gray matter volume (GMV) and spontaneous functional connectivity (FC) changes in patients with chronic Leber's hereditary optic neuropathy (LHON), and their relations with clinical measures.

Methods

A total of 32 patients with chronic LHON and matched sighted healthy controls (HC) underwent neuro-ophthalmologic examinations and multimodel magnetic resonance imaging (MRI) scans. Voxel-based morphometry (VBM) was used to detect the GMV differences between the LHON and HC. Furthermore, resting-state FC analysis using the VBM-identified clusters as seeds was carried out to detect potential functional reorganization in the LHON. Finally, the associations between the neuroimaging and clinical measures were performed.

Results

The average peripapillary retinal nerve fiber layer (RNFL) thickness of the chronic LHON was significantly thinner (T = −16.421, p < 0.001), and the mean defect of the visual field was significantly higher (T = 11.28, p < 0.001) than the HC. VBM analysis demonstrated a significantly lower GMV of bilateral calcarine gyri (CGs) in the LHON than in the HC (p < 0.05). Moreover, in comparison with the HC, the LHON had significantly lower FC between the centroid of the identified left CG and ipsilateral superior occipital gyrus (SOG) and higher FC between this cluster and the ipsilateral posterior cingulate gyrus (p < 0.05, corrected). Finally, the GMV of the left CG was negatively correlated with the LHON duration (r = −0.535, p = 0.002), and the FC between the left CG and the ipsilateral posterior cingulate gyrus of the LHON was negatively correlated with the average peripapillary RNFL thickness (r = −0.522, p = 0.003).

Conclusion

The atrophied primary visual cortex of the chronic LHON may be caused by transneuronal degeneration following the retinal damage. Moreover, our findings suggest that the functional organization of the atrophied primary visual cortex has been reshaped in the chronic LHON.

Photoreceptor Manifestations of Primary Mitochondrial Optic Nerve Disorders

Purpose

To compare the manifestations of photoreceptors (PRs) in three hereditary optic neuropathies affected by primary mitochondrial dysfunction and discuss whether the retinal ganglion cells (RGCs) or the PRs are preferentially affected.

Methods

A retrospective analysis of patients with genetically confirmed diagnoses of optic neuropathies associated with mitochondrial dysfunction was performed. This cohort included Leber's hereditary optic neuropathy (LHON), autosomal dominant optic atrophy type 1 (OPA1), and optic atrophy type 13 (OPA13). Patient chart evaluations included clinical characteristics, best-corrected visual acuity (BCVA), fundus photography, spectral-domain optical coherence tomography (SD-OCT), electroretinogram (ERG), and visual evoked potential data.

Results

This analysis included seven patients with LHON, six with OPA1, and one with OPA13 from a tertiary medical center. Thirteen of the 14 individuals were male. The average BCVA at diagnosis was 20/285 and 20/500 in the right and left eyes, respectively. Five of the seven patients with LHON, and three of the six patients with OPA1 also showed a mild amplitude reduction or delayed latency on light-adapted ERG and 30-Hz flicker responses; however, SD-OCT imaging did not show correlated PR abnormalities. Notably, a 7-year follow-up of a patient with OPA13 revealed degeneration of RGCs prior to the degeneration of PRs. Follow-up data also demonstrated continuous loss of cone outer segment tips on SD-OCT imaging.

Conclusions

RGCs are, in general, affected by mitochondrial dysfunction, whereas variable PR dysfunction exists in patients with LHON and OPA1, especially with respect to the cone responses. Involvement of PRs is particularly evident in OPA13 after RGC degenerations.

Gene therapy restores mitochondrial function and protects retinal ganglion cells in optic neuropathy induced by a mito-targeted mutant ND1 gene

Therapies for genetic disorders caused by mutated mitochondrial DNA are an unmet need, in large part due barriers in delivering DNA to the organelle and the absence of relevant animal models. We injected into mouse eyes a mitochondrially targeted Adeno-Associated-Virus (MTS-AAV) to deliver the mutant human NADH ubiquinone oxidoreductase subunit I (hND1/m.3460G>A) responsible for Leber’s hereditary optic neuropathy, the most common primary mitochondrial genetic disease. We show that the expression of the mutant hND1 delivered to retinal ganglion cells (RGC) layer colocalizes with the mitochondrial marker PORIN and the assembly of the expressed hND1 protein into host respiration complex I. The hND1 injected eyes exhibit hallmarks of the human disease with progressive loss of RGC function and number, as well as optic nerve degeneration. We also show that gene therapy in the hND1 eyes by means of an injection of a second MTS-AAV vector carrying wild type human ND1 restores mitochondrial respiratory complex I activity, the rate of ATP synthesis and protects RGCs and their axons from dysfunction and degeneration. These results prove that MTS-AAV is a highly efficient gene delivery approach with the ability to create mito-animal models and has the therapeutic potential to treat mitochondrial genetic diseases.

Natural history of patients with Leber hereditary optic neuropathy-results from the REALITY study

BACKGROUND/OBJECTIVES

REALITY is an international observational retrospective registry of LHON patients evaluating the visual course and outcome in Leber hereditary optic neuropathy (LHON).

SUBJECTS/METHODS

Demographics and visual function data were collected from medical charts of LHON patients with visual loss. The study was conducted in 11 study centres in the United States of America and Europe. The collection period extended from the presymptomatic stage to at least more than one year after onset of vision loss (chronic stage). A Locally Weighted Scatterplot Smoothing (LOWESS) local regression model was used to analyse the evolution of best-corrected visual acuity (BCVA) over time.

RESULTS

44 LHON patients were included; 27 (61%) carried the m.11778G>A ND4 mutation, 8 (18%) carried the m.3460G>A ND1 mutation, and 9 (20%) carried the m.14484T>C ND6 mutation. Fourteen (32%) patients were under 18 years old at onset of vision loss and 5 (11%) were below the age of 12. The average duration of follow-up was 32.5 months after onset of symptoms. At the last observed measure, mean BCVA was 1.46 LogMAR in ND4 patients, 1.52 LogMAR in ND1 patients, and 0.97 LogMAR in ND6 patients. The worst visual outcomes were reported in ND4 patients aged at least 15 years old at onset, with a mean BCVA of 1.55 LogMAR and no tendency for spontaneous recovery. The LOESS modelling curve depicted a severe and permanent deterioration of BCVA.

CONCLUSIONS

Amongst LHON patients with the three primary mtDNA mutations, adult patients with the m.11778G>A ND4 mutation had the worst visual outcomes, consistent with prior reports.

Chemotherapy-induced cachexia and model-informed dosing to preserve lean mass in cancer treatment

Although chemotherapy is a standard treatment for cancer, it comes with significant side effects. In particular, certain agents can induce severe muscle loss, known as cachexia, worsening patient quality of life and treatment outcomes. 5-fluorouracil, an anti-cancer agent used to treat several cancers, has been shown to cause muscle loss. Experimental data indicates a non-linear dose-dependence for muscle loss in mice treated with daily or week-day schedules. We present a mathematical model of chemotherapy-induced muscle wasting that captures this non-linear dose-dependence. Area-under-the-curve metrics are proposed to quantify the treatment’s effects on lean mass and tumour control. Model simulations are used to explore alternate dosing schedules, aging effects, and morphine use in chemotherapy treatment with the aim of better protecting lean mass while actively targeting the tumour, ultimately leading to improved personalization of treatment planning and improved patient quality of life.

In this paper we present a novel mathematical model for muscle loss due to cancer chemotherapy treatment. Loss of muscle mass relates to increased drug toxicity and side-effects, and to decreased patient quality of life and survival rates. With our model, we examine the therapeutic efficacy of various dosing schedules with the aim of controlling a growing tumour while also preserving lean mass. Preservation of body composition, in addition to consideration of inflammation and immune interactions, the gut microbiome, and other systemic health measures, may lead to improved patient-specific treatment plans that improve patient quality of life.

Biallelic Loss-of-Function NDUFA12 Variants Cause a Wide Phenotypic Spectrum from Leigh/Leigh-Like Syndrome to Isolated Optic Atrophy

BACKGROUND

Biallelic loss-of-function NDUFA12 variants have hitherto been linked to mitochondrial complex I deficiency presenting with heterogeneous clinical and radiological features in nine cases only.

OBJECTIVES

To fully characterize, both phenotypically and genotypically, NDUFA12-related mitochondrial disease.

METHODS

We collected data from cases identified by screening genetic databases of several laboratories worldwide and systematically reviewed the literature.

RESULTS

Nine unreported NDUFA12 cases from six pedigrees were identified, with presentation ranging from movement disorder phenotypes (dystonia and/or spasticity) to isolated optic atrophy. MRI showed basal ganglia abnormalities (n = 6), optic atrophy (n = 2), or was unremarkable (n = 1). All carried homozygous truncating NDUFA12 variants, three of which are novel.

CONCLUSIONS

Our case series expands phenotype-genotype correlations in NDUFA12-associated mitochondrial disease, providing evidence of intra- and inter-familial clinical heterogeneity for the same variant. It confirms NDUFA12 variants should be included in the diagnostic workup of Leigh/Leigh-like syndromes - particularly with dystonia - as well as isolated optic atrophy.

Mitochondrial Dynamics and Mitochondria-Lysosome Contacts in Neurogenetic Diseases

Mitochondrial network is constantly in a dynamic and regulated balance of fusion and fission processes, which is known as mitochondrial dynamics. Mitochondria make physical contacts with almost every other membrane in the cell thus impacting cellular functions. Mutations in mitochondrial dynamics genes are known to cause neurogenetic diseases. To better understand the consequences on the cellular phenotype and pathophysiology of neurogenetic diseases associated with defective mitochondrial dynamics, we have compared the fibroblasts phenotypes of (i) patients carrying pathogenic variants in genes involved in mitochondrial dynamics such as DRP1 (also known as DNM1L), GDAP1, OPA1, and MFN2, and (ii) patients carrying mutated genes that their dysfunction affects mitochondria or induces a mitochondrial phenotype, but that are not directly involved in mitochondrial dynamic network, such as FXN (encoding frataxin, located in the mitochondrial matrix), MED13 (hyperfission phenotype), and CHKB (enlarged mitochondria phenotype). We identified mitochondrial network alterations in all patients’ fibroblasts except for CHKBQ198*/Q198*. Functionally, all fibroblasts showed mitochondrial oxidative stress, without membrane potential abnormalities. The lysosomal area and distribution were abnormal in GDAP1W67L/W67L, DRP1K75E/+, OPA1F570L/+, and FXNR165C/GAA fibroblasts. These lysosomal alterations correlated with mitochondria-lysosome membrane contact sites (MCSs) defects in GDAP1W67L/W67L exclusively. The study of mitochondrial contacts in all samples further revealed a significant decrease in MFN2R104W/+ fibroblasts. GDAP1 and MFN2 are outer mitochondrial membrane (OMM) proteins and both are related to Charcot-Marie Tooth neuropathy. Here we identified their constitutive interaction as well as MFN2 interaction with LAMP-1. Therefore MFN2 is a new mitochondria-lysosome MCSs protein. Interestingly, GDAP1W67L/W67L and MFN2R104W/+ fibroblasts carry pathogenic changes that occur in their catalytic domains thus suggesting a functional role of GDAP1 and MFN2 in mitochondria–lysosome MCSs. Finally, we observed starvation-induced autophagy alterations in DRP1K75E/+, GDAP1W67L/W67L, OPA1F570L/+, MFN2R104W/+, and CHKBQ198*/Q198* fibroblasts. These genes are related to mitochondrial membrane structure or lipid composition, which would associate the OMM with starvation-induced autophagy. In conclusion, the study of mitochondrial dynamics and mitochondria-lysosome axis in a group of patients with different neurogenetic diseases has deciphered common and unique cellular phenotypes of degrading and non-degrading pathways that shed light on pathophysiological events, new biomarkers and pharmacological targets for these disorders.