Visual electrophysiologic findings in patients from an extensive Brazilian family with Leber's hereditary optic neuropathy

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.

Electroretinographic oscillatory potentials in Leber hereditary optic neuropathy

PURPOSE

Leber hereditary optic neuropathy (LHON) affects retinal ganglion cells causing severe vision loss. Pattern electroretinogram and photopic negative response (PhNR) of the light-adapted (LA) full-field electroretinogram (ERG) are typically affected in LHON. In the present study, we evaluated dark-adapted (DA) and LA oscillatory potentials (OPs) of the flash ERG in genetically characterized LHON patients to dissociate slow from fast components of the response.

METHODS

Seven adult patients (mean age = 28.4 ± 5.6) in whom genetic diagnosis confirmed LHON with mtDNA or nuclear DNAJC30 (arLHON) pathogenic variants were compared to 12 healthy volunteers (mean age = 35.0 ± 12.1). Full-field ERGs were recorded from both eyes. Offline digital filters at 50, 75 and 100 Hz low cutoff frequencies were applied to isolate high-frequency components from the original ERG signals.

RESULTS

ERG a-waves and b-waves were comparable between LHON patients and controls, while PhNR was significantly reduced (p = 0.009) in LHON patients compared to controls, as expected. OPs derived from DA signals (75 Hz low cutoff frequency) showed reduced peak amplitude for OP2 (p = 0.019). LA OP differences between LHON and controls became significant (OP2: p = 0.047, OP3: p = 0.039 and OP4: p = 0.013) when the 100 Hz low-cutoff frequency filter was applied.

CONCLUSIONS

Reduced OPs in LHON patients may represent disturbed neuronal interactions in the inner retina with preserved photoreceptoral (a-wave) to bipolar cell (b-wave) activation. Reduced DA OP2 and high-cutoff LA OP alterations may be further explored as functional measures to characterize LHON status and progression.

Development of a deep learning model to distinguish the cause of optic disc atrophy using retinal fundus photography

The differential diagnosis for optic atrophy can be challenging and requires expensive, time-consuming ancillary testing to determine the cause. While Leber's hereditary optic neuropathy (LHON) and optic neuritis (ON) are both clinically significant causes for optic atrophy, both relatively rare in the general population, contributing to limitations in obtaining large imaging datasets. This study therefore aims to develop a deep learning (DL) model based on small datasets that could distinguish the cause of optic disc atrophy using only fundus photography. We retrospectively reviewed fundus photographs of 120 normal eyes, 30 eyes (15 patients) with genetically-confirmed LHON, and 30 eyes (26 patients) with ON. Images were split into a training dataset and a test dataset and used for model training with ResNet-18. To visualize the critical regions in retinal photographs that are highly associated with disease prediction, Gradient-Weighted Class Activation Map (Grad-CAM) was used to generate image-level attention heat maps and to enhance the interpretability of the DL system. In the 3-class classification of normal, LHON, and ON, the area under the receiver operating characteristic curve (AUROC) was 1.0 for normal, 0.988 for LHON, and 0.990 for ON, clearly differentiating each class from the others with an overall total accuracy of 0.93. Specifically, when distinguishing between normal and disease cases, the precision, recall, and F1 scores were perfect at 1.0. Furthermore, in the differentiation of LHON from other conditions, ON from others, and between LHON and ON, we consistently observed precision, recall, and F1 scores of 0.8. The model performance was maintained until only 10% of the pixel values of the image, identified as important by Grad-CAM, were preserved and the rest were masked, followed by retraining and evaluation.

Leber Hereditary Optic Neuropathy in a Family of Carriers of MT-ND5 m.13042G>T (A236S) Novel Variant

BACKGROUND

A Slovenian three-generation family with 3 individuals with bilateral optic neuropathy and 2 unaffected relatives with a novel homoplasmic missense variant m.13042G > T (A236S) in the ND5 gene is described. A detailed phenotype at initial diagnosis and a follow-up of bilateral optic neuropathy progression is presented for 2 affected individuals.

METHODS

A detailed phenotype analysis with clinical examination in the early and chronic phase with electrophysiology and OCT segmentation is presented. Genotype analysis with full mitochondrial genome sequencing was performed.

RESULTS

Two affected male individuals (maternal cousins) had a profound visual loss at an early age (11 and 20 years) with no recovery. The maternal grandmother exhibited bilateral optic atrophy with a history of visual loss at the age 58 years. The visual loss of both affected male individuals was characterized by centrocecal scotoma, abnormal color vision, abnormal PERG N95, and VEP. Later with disease progression, retinal nerve fiber layer thinning was observed on OCT. We observed no other extraocular clinical features. Mitochondrial sequencing identified a homoplasmic novel variant m.13042G > T (A236S) in the MT-ND5 gene, belonging to a haplogroup K1a.

CONCLUSIONS

Novel homoplasmic variant m.13042G > T (A236S) in the ND5 gene in our family was associated with Leber hereditary optic neuropathy-like phenotype. However, predicting the pathogenicity of a novel ultra-rare missense variant in the mitochondrial ND5 gene is challenging. Genetic counseling should consider genotypic and phenotypic heterogeneity, incomplete penetrance, haplogroup type, and tissue-specific thresholds.

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.

Impaired Ganglion Cell Function Objectively Assessed by the Photopic Negative Response in Affected and Asymptomatic Members From Brazilian Families With Leber's Hereditary Optic Neuropathy

Purpose: The photopic negative response (PhNR) is an electrophysiological method that provides retinal ganglion cell function assessment using full-field stimulation that does not require clear optics or refractive correction. The purpose of this study was to assess ganglion cell function by PhNR in affected and asymptomatic carriers from Brazilian families with LHON. Methods: Individuals either under suspicion or previously diagnosed with LHON and their family members were invited to participate in this cross-sectional study. Screening for the most frequent LHON mtDNA mutations was performed. Visual acuity, color discrimination, visual fields, pattern-reversal visual evoked potentials (PRVEP), full-field electroretinography and PhNR were tested. A control group of healthy subjects was included. Full-field ERG PhNR were recorded using red (640 nm) flashes at 1 cd.s/m², on blue (470 nm) rod saturating background. PhNR amplitude (μV) was measured using baseline-to-trough (BT). Optical coherence tomography scans of both the retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC) were measured. PhNR amplitudes among affected, carriers and controls were compared by Kruskal-Wallis test followed by post-hoc Dunn test. The associations between PhNR amplitude and OCT parameters were analyzed by Spearman rank correlation. Results: Participants were 24 LHON affected patients (23 males, mean age=30.5 ± 11.4 yrs) from 19 families with the following genotype: m.11778G>A [N = 15 (62%), 14 males]; m.14484T>C [N = 5 (21%), all males] and m.3460G>A [N = 4 (17%), all males] and 14 carriers [13 females, mean age: 43.2 ± 13.3 yrs; m.11778G>A (N = 11); m.3460G>A (N = 2) and m.14484T>C (N = 1)]. Controls were eight females and seven males (mean age: 32.6 ± 11.5 yrs). PhNR amplitudes were significantly reduced (p = 0.0001) in LHON affected (-5.96 ± 3.37 μV) compared to carriers (-16.53 ± 3.40 μV) and controls (-23.91 ± 4.83; p < 0.0001) and in carriers compared to controls (p = 0.01). A significant negative correlation was found between PhNR amplitude and total macular ganglion cell thickness (r = -0.62, p < 0.05). Severe abnormalities in color discrimination, visual fields and PRVEPs were found in affected and subclinical abnormalities in carriers. Conclusions: In this cohort of Brazilian families with LHON the photopic negative response was severely reduced in affected patients and mildly reduced in asymptomatic carriers suggesting possible subclinical abnormalities in the latter. These findings were similar among pathogenic mutations.

Visual Evoked Potentials in Joubert Syndrome: A Suggested Useful Method for Evaluating Future Approaches Targeted to Improve Visual Pathways' Function

Introduction

Joubert syndrome (JS) is a recessive disorder characterized by a congenital malformation of the mid-hindbrain and a large spectrum of clinical features including optic nerve morphologic abnormalities. The function of the visual pathways, including the optic nerve, can be objectively evaluated by visual evoked potential (VEP) recordings. Our work aims to employ VEP to evaluate the neural conduction along the visual pathways in JS patients with or without optic nerve morphologic abnormalities (ONMA).

Methods

In this observational and prospective study, 18 children with genetic diagnosis of JS (mean age 8.78 ± 5.87 years) and 17 healthy age-similar control subjects (control group, 9.05 ± 6.02 years) were enrolled.

Based on presence/absence of ONMA at fundus examination, JS patients were divided into two groups: the JS-A group (eight patients with ONMA) and JS-N group (ten patients without ONMA). Following the ISCEV standards, pattern VEPs were recorded in patients and controls in response to 60’ and 15’ checks to obtain a prevalent activation of large or small axons, respectively.

Results

Compared to controls, both the JS-A and JS-N groups showed significant abnormalities in 60’ and 15’ VEP implicit time and amplitude. Only in the JS-N group were values of 15’ VEP implicit significantly correlated with the corresponding values of visual acuity.

Conclusions

Our results suggest that a visual pathways dysfunction (of both large and small axons) detectable by VEP may occur in JS patients regardless of the presence of ONMA. Since clinical trials are envisaged in the near future to address JS-related ocular problems, our results might provide information about the potential usefulness of VEP recordings to assess the efficacy of treatments targeted to improve the visual pathways’ function.

Foveal pit morphological changes in asymptomatic carriers of the G11778A mutation with Leber's hereditary optic neuropathy

AIM

To investigate the foveal pit morphology changes in unaffected carriers and affected Leber's hereditary optic neuropathy (LHON) patients with the G11778A mutation from one family.

METHODS

This study was a prospective cross-sectional study. Both eyes from 16 family members (age from 9 to 47y) with the G11778A mutation were analyzed and compared with 1 eye from 20 normal control subjects. Eleven family members with the G11778A mutation but without optic neuropathy were classified as unaffected carriers (n=22 eyes). Five family members (n=10 eyes) expressed the LHON phenotype and were classified as affected patients. Retinal images of all the subjects were taken by optical coherence tomography (OCT), and an automatic algorithm was used to segment the retina to eight layers. Horizontal and vertical OCT images centered on the fovea were used to measure intra-retinal layer thicknesses and foveal morphometry.

RESULTS

Thicker foveal thickness, thinner foveal pit depth, and flatter foveal slopes were observed in unaffected carriers and affected LHON patients (all P<0.001). Further, the slopes of all four sectors in the LHON were flatter than those in the unaffected carriers (all P<0.001). Compared with the control group, affected LHON patients had a thinner retinal nerve fiber layer (RNFL), ganglion cell layer and inner plexiform layer (GCL+IPL), and total retina (all P<0.01). The retinal nerve fiber layer (RNFL) of affected patients was 38.0% thinner than that of controls while the GCL+IPL was 40.1% thinner.

CONCLUSION

The foveal pit morphology shows changes in both unaffected carriers and affects patients. RNFL and GCL+IPL are thinner in affected LHON patients but not in unaffected carriers.

Photoreceptors in a mouse model of Leigh syndrome are capable of normal light-evoked signaling

Mitochondrial dysfunction is an important cause of heritable vision loss. Mutations affecting mitochondrial bioenergetics may lead to isolated vision loss or life-threatening systemic disease, depending on a mutation's severity. Primary optic nerve atrophy resulting from death of retinal ganglion cells is the most prominent ocular manifestation of mitochondrial disease. However, dysfunction of other retinal cell types has also been described, sometimes leading to a loss of photoreceptors and retinal pigment epithelium that manifests clinically as pigmentary retinopathy. A popular mouse model of mitochondrial disease that lacks NADH:ubiquinone oxidoreductase subunit S4 (NDUFS4), a subunit of mitochondrial complex I, phenocopies many traits of the human disease Leigh syndrome, including the development of optic atrophy. It has also been reported that ndufs4 ^-/- mice display diminished light responses at the level of photoreceptors or bipolar cells. By conducting electroretinography (ERG) recordings in live ndufs4 ^-/- mice, we now demonstrate that this defect occurs at the level of retinal photoreceptors. We found that this deficit does not arise from retinal developmental anomalies, photoreceptor degeneration, or impaired regeneration of visual pigment. Strikingly, the impairment of ndufs4 ^-/- photoreceptor function was not observed in ex vivo ERG recordings from isolated retinas, indicating that photoreceptors with complex I deficiency are intrinsically capable of normal signaling. The difference in electrophysiological phenotypes in vivo and ex vivo suggests that the energy deprivation associated with severe mitochondrial impairment in the outer retina renders ndufs4 ^-/- photoreceptors unable to maintain the homeostatic conditions required to operate at their normal capacity.

Unilateral cone-rod dysfunction and retinal thinning in a child carrying the 14484 mutation of Leber hereditary optic neuropathy

Leber hereditary optic neuropathy is a mitochondrial disorder that presents with bilateral, usually sequential, central vision loss from optic nerve damage. We report the case of an 11-year-old girl with the 14484 mutation who developed significant, unilateral visual loss secondary to retinal thinning and abnormal cone-rod responses on electroretinography, with no evidence of optic nerve damage. Patients carrying the 14484 mutation may also develop cone-rod dysfunction.

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.

Leber Hereditary Optic Neuropathy: Exemplar of an mtDNA Disease

The report in 1988 that Leber Hereditary Optic Neuropathy (LHON) was the product of mitochondrial DNA (mtDNA) mutations provided the first demonstration of the clinical relevance of inherited mtDNA variation. From LHON studies, the medical importance was demonstrated for the mtDNA showing its coding for the most important energy genes, its maternal inheritance, its high mutation rate, its presence in hundreds to thousands of copies per cell, its quantitatively segregation of biallelic genotypes during both mitosis and meiosis, its preferential effect on the most energetic tissues including the eye and brain, its wide range of functional polymorphisms that predispose to common diseases, and its accumulation of mutations within somatic tissues providing the aging clock. These features of mtDNA genetics, in combination with the genetics of the 1-2000 nuclear DNA (nDNA) coded mitochondrial genes, is not only explaining the genetics of LHON but also providing a model for understanding the complexity of many common diseases. With the maturation of LHON biology and genetics, novel animal models for complex disease have been developed and new therapeutic targets and strategies envisioned, both pharmacological and genetic. Multiple somatic gene therapy approaches are being developed for LHON which are applicable to other mtDNA diseases. Moreover, the unique cytoplasmic genetics of the mtDNA has permitted the first successful human germline gene therapy via spindle nDNA transfer from mtDNA mutant oocytes to enucleated normal mtDNA oocytes. Such LHON lessons are actively being applied to common ophthalmological diseases like glaucoma and neurological diseases like Parkinsonism.

Leber hereditary optic neuropathy: current perspectives

Leber hereditary optic neuropathy (LHON) is one of the most common inherited optic neuropathies causing bilateral central vision loss. The disorder results from point mutations in mitochondrial DNA and subsequent mitochondrial dysfunction. The primary cell type that is lost in LHON is the retinal ganglion cell, which is highly susceptible to disrupted ATP production and oxidative stress. Inheritance of LHON follows that of mitochondrial genetics, and it has a highly variable clinical phenotype, as other genetic and environmental factors also play a role. Although LHON usually presents with isolated vision loss, some patients suffer other neurological sequelae. For ill-defined reasons, male LHON mutation carriers are more affected than females. Most LHON patients remain legally blind, but a small proportion can experience spontaneous partial recovery, often within the first year of symptom onset. Unfortunately, at this time there are no established curative interventions and treatment is largely supportive. Patients should be offered low vision services and counseled on mitigating risk factors for additional vision loss, such as smoking and consuming alcohol. Encouraging treatments currently undergoing investigation includes ubiquinone analogs, such as idebenone, as well as gene therapy and stem cells to restore ATP synthesis and provide neuroprotection to surviving retinal ganglion cells.

Gene therapy for mitochondrial diseases: Leber Hereditary Optic Neuropathy as the first candidate for a clinical trial

Mitochondrial disorders cannot be ignored anymore in most medical disciplines; indeed their minimum estimated prevalence is superior to 1 in 5000 births. Despite the progress made in the last 25 years on the identification of gene mutations causing mitochondrial pathologies, only slow progress was made towards their effective treatments. Ocular involvement is a frequent feature in mitochondrial diseases and corresponds to severe and irreversible visual handicap due to retinal neuron loss and optic atrophy. Interestingly, three clinical trials for Leber Congenital Amaurosis due to RPE65 mutations are ongoing since 2007. Overall, the feasibility and safety of ocular Adeno-Associated Virus delivery in adult and younger patients and consistent visual function improvements have been demonstrated. The success of gene-replacement therapy for RPE65 opens the way for the development of similar approaches for a broad range of eye disorders, including those with mitochondrial etiology such as Leber Hereditary Optic Neuropathy (LHON).

Mathematically modeling the involvement of axons in Leber's hereditary optic neuropathy

PURPOSE

Leber's hereditary optic neuropathy (LHON), a mitochondrial disease, has clinical manifestations that reflect the initial preferential involvement of the papillomacular bundle (PMB). The present study seeks to predict the order of axonal loss in LHON optic nerves using the Nerve Fiber Layer Stress Index (NFL-S(I)), which is a novel mathematical model.

METHODS

Optic nerves were obtained postmortem from four molecularly characterized LHON patients with varying degrees of neurodegenerative changes and three age-matched controls. Tissues were cut in cross-section and stained with p-phenylenediamine to visualize myelin. Light microscopic images were captured in 32 regions of each optic nerve. Control and LHON tissues were evaluated by measuring axonal dimensions to generate an axonal diameter distribution map. LHON tissues were further evaluated by determining regions of total axonal depletion.

RESULTS

A size gradient was evident in the control optic nerves, with average axonal diameter increasing progressively from the temporal to nasal borders. LHON optic nerves showed an orderly loss of axons, starting inferotemporally, progressing centrally, and sparing the superonasal region until the end. Values generated from the NFL-S(I) equation fit a linear regression curve (R(2) = 0.97; P < 0.001).

CONCLUSIONS

The quantitative histopathologic data from this study revealed that the PMB is most susceptible in LHON, supporting clinical findings seen early in the course of disease onset. The present study also showed that the subsequent progression of axonal loss within the optic nerve can be predicted precisely with the NFL-S(I) equation. The results presented provided further insight into the pathophysiology of LHON.

Mouse mtDNA mutant model of Leber hereditary optic neuropathy

An animal model of Leber hereditary optic neuropathy (LHON) was produced by introducing the human optic atrophy mtDNA ND6 P25L mutation into the mouse. Mice with this mutation exhibited reduction in retinal function by elecroretinogram (ERG), age-related decline in central smaller caliber optic nerve fibers with sparing of larger peripheral fibers, neuronal accumulation of abnormal mitochondria, axonal swelling, and demyelination. Mitochondrial analysis revealed partial complex I and respiration defects and increased reactive oxygen species (ROS) production, whereas synaptosome analysis revealed decreased complex I activity and increased ROS but no diminution of ATP production. Thus, LHON pathophysiology may result from oxidative stress.

Adeno-associated virus-mediated gene delivery of the human ND4 complex I subunit in rabbit eyes

BACKGROUND

To assess intravitreal injection dose and safety of recombinant adeno-associated virus-mediated gene delivery of human NADH dehydrogenase subunit 4 (ND4) in rabbit eyes.

METHODS

An open reading frame for human ND4 or adeno-associated virus-green fluorescent protein were fused to the mitochondrial targeting sequence and packed into separate adeno-associated virus capsids. Rabbits of three treatment groups were administered 0.1 mL adeno-associated virus-ND4, 0.1 mL adeno-associated virus-green fluorescent protein or 0.1 mL vehicle via intravitreal injection, respectively. The safety of recombinant adenoassociated virus-mediated gene delivery of human ND4 in rabbit eyes was assessed with a slit-lamp microscope and direct ophthalmoscope, measurements of intraocular pressure and flash visual evoked potential, and optical coherence tomography. The mRNA and protein expressions of human ND4 in the retina of rabbits were determined with real-time polymer chain reaction (PCR), immunofluorescence and Western blot.

RESULTS

No complications occurred in any of the three treatment groups after the intravitreal injection. At 1-month post-injection, no significant difference in the mean thickness of retinal nerve fibre layer was found among the three groups. Results of the visual evoked potential test showed that there was no difference in the latency of the visual P100 wave among the three groups. Real-time PCR, immunofluorescence and Western blot analyses verified the expressions of ND4 and green fluorescent protein in the retinal nerve fibre layer.

CONCLUSIONS

Intravitreal injection of adeno-associated virus-ND4 expression vectors was effectively and safely performed in our study. The data on the dose and method of intravitreal injection from our study will provide a valuable reference for clinical intravitreal injection of adeno-associated virus-ND4 for the treatment of Leber's hereditary optic neuropathy.

Mitochondrial optic neuropathies - disease mechanisms and therapeutic strategies

Leber hereditary optic neuropathy (LHON) and autosomal-dominant optic atrophy (DOA) are the two most common inherited optic neuropathies in the general population. Both disorders share striking pathological similarities, marked by the selective loss of retinal ganglion cells (RGCs) and the early involvement of the papillomacular bundle. Three mitochondrial DNA (mtDNA) point mutations; m.3460G>A, m.11778G>A, and m.14484T>C account for over 90% of LHON cases, and in DOA, the majority of affected families harbour mutations in the OPA1 gene, which codes for a mitochondrial inner membrane protein. Optic nerve degeneration in LHON and DOA is therefore due to disturbed mitochondrial function and a predominantly complex I respiratory chain defect has been identified using both in vitro and in vivo biochemical assays. However, the trigger for RGC loss is much more complex than a simple bioenergetic crisis and other important disease mechanisms have emerged relating to mitochondrial network dynamics, mtDNA maintenance, axonal transport, and the involvement of the cytoskeleton in maintaining a differential mitochondrial gradient at sites such as the lamina cribosa. The downstream consequences of these mitochondrial disturbances are likely to be influenced by the local cellular milieu. The vulnerability of RGCs in LHON and DOA could derive not only from tissue-specific, genetically-determined biological factors, but also from an increased susceptibility to exogenous influences such as light exposure, smoking, and pharmacological agents with putative mitochondrial toxic effects. Our concept of inherited mitochondrial optic neuropathies has evolved over the past decade, with the observation that patients with LHON and DOA can manifest a much broader phenotypic spectrum than pure optic nerve involvement. Interestingly, these phenotypes are sometimes clinically indistinguishable from other neurodegenerative disorders such as Charcot-Marie-Tooth disease, hereditary spastic paraplegia, and multiple sclerosis, where mitochondrial dysfunction is also thought to be an important pathophysiological player. A number of vertebrate and invertebrate disease models has recently been established to circumvent the lack of human tissues, and these have already provided considerable insight by allowing direct RGC experimentation. The ultimate goal is to translate these research advances into clinical practice and new treatment strategies are currently being investigated to improve the visual prognosis for patients with mitochondrial optic neuropathies.

Alterations in multifocal visual evoked potentials during the acute phase of Leber's hereditary optic neuropathy

PURPOSE

This report aimed to investigate alterations in multifocal visual evoked potentials (mfVEPs) during the acute stage of Leber's hereditary optic neuropathy (LHON).

METHODS

A 27-year-old woman with a point mutation at nucleotide 11778 in the mitochondrial DNA was examined during the acute phase of LHON, which is generally investigated only rarely because of its rapid progress. She was examined repeatedly, with testing of best corrected visual acuity, pupil function, Goldmann perimetry, ophthalmoscopy and frequent assessment of mfVEPs.

RESULTS

Multifocal VEPs, which reveal topographical information about different parts of the visual pathways, demonstrated reduced responses in all parts of the central visual field. The mean amplitude (summarized amplitude of the first two components) in the mfVEPs in the previously described sector C, which has been identified as a hallmark of other optic nerve disorders, was evaluated. This amplitude demonstrated a correlation with the progression of the disease during the acute period of LHON, which also correlated with the VA, pupil function and Goldmann perimetry.

CONCLUSIONS

These alterations in the components of mfVEPs reflect the reduction in the function of the visual pathways in different parts of the central field; the drop in amplitude in a localized area (sector C), not previously described, demonstrates the acute course of this disorder. Multifocal VEPs may be of further interest in evaluating the pathogenesis of this disorder and of clinical value in representing an objective method for monitoring the course of this disease.

Haplogroup effects and recombination of mitochondrial DNA: novel clues from the analysis of Leber hereditary optic neuropathy pedigrees

The mitochondrial DNA (mtDNA) of 87 index cases with Leber hereditary optic neuropathy (LHON) sequentially diagnosed in Italy, including an extremely large Brazilian family of Italian maternal ancestry, was evaluated in detail. Only seven pairs and three triplets of identical haplotypes were observed, attesting that the large majority of the LHON mutations were due to independent mutational events. Assignment of the mutational events into haplogroups confirmed that J1 and J2 play a role in LHON expression but narrowed the association to the subclades J1c and J2b, thus suggesting that two specific combinations of amino acid changes in the cytochrome b are the cause of the mtDNA background effect and that this may occur at the level of the supercomplex formed by respiratory-chain complexes I and III. The families with identical haplotypes were genealogically reinvestigated, which led to the reconnection into extended pedigrees of three pairs of families, including the Brazilian family with its Italian counterpart. The sequencing of entire mtDNA samples from the reconnected families confirmed the genealogical reconstruction but showed that the Brazilian family was heteroplasmic at two control-region positions. The survey of the two sites in 12 of the Brazilian subjects revealed triplasmy in most cases, but there was no evidence of the tetraplasmy that would be expected in the case of mtDNA recombination.