Ophthalmologic findings in a large pedigree of 11778/Haplogroup J Leber hereditary optic neuropathy

[Leber's hereditary optic neuropathy]

Leber's hereditary optic atrophy (LHON) is a genetic optic neuropathy that is more prevalent in young males but can occur from childhood to old age. The primary cause is mitochondrial genetic mutations, which are associated with dysfunction of mitochondrial electron transport chain complex I. It manifests as acute to subacute visual impairment, often starting unilaterally but progressing to involve both eyes within weeks to months. Visual loss is severe, with many patients having corrected visual acuity below 0.1. The differential diagnosis of optic neuritis is essential, and assessments such as pupillary light reflex, fluorescein fundus angiography, and magnetic resonance imaging can be useful for differentiation. LHON should be considered as one of the differential diagnoses for optic neuritis, and collaboration between neurologists and ophthalmologists is crucial for accurate diagnosis and appropriate treatment.

Clinical Characteristics of m.11778G>A Leber Hereditary Optic Neuropathy with Favorable Outcomes

The prognosis of 11,778 mitochondrial mutations in Leber hereditary optic neuropathy (LHON) is poor. Patients with favorable outcomes (visual acuity better than 20/100) who could be observed for more than 6 months were analyzed. Among 74 patients (57 male, 17 female), 6 (8.1%) showed improvement in visual acuity of 20/100 or higher. The patients with favorable outcomes have better visual acuity at nadir (logMAR 0.98 ± 0.69 in the favorable patients and logMAR 2.32 ± 0.93 in the unfavorable patients, p = .003). Among the favorable group, four patients (36, 32, 19, and 7 years of age at onset) took idebenone within 6 months of onset. However, fifty-one percent of the patients with unfavorable outcomes took idebenone (p = .008). Although the age at onset in the favorable patients is relatively younger than that of the unfavorable patients (20.3 ± 10.8 versus 28.8 ± 12.8 years), a significant difference was not found (p = .138). In conclusion, better visual acuity in nadir and administration of idebenone may affect vision recovery.

Vascular Changes in the Macula of Patients after Previous Episodes of Vision Loss Due to Leber Hereditary Optic Neuropathy and Non-Arteritic Ischemic Optic Neuropathy

PURPOSE

to assess the vasculature and thickness of the macula using OCT-A in patients who had experienced a previous episode of Leber hereditary optic neuropathy (LHON) or non-arteritic anterior ischemic optic neuropathy (NA-AION).

METHODS

twelve eyes with chronic LHON and ten eyes with chronic NA-AION and eight NA-AION fellow eyes were examined using OCT-A. The vessel density was measured in the superficial and deep plexus of the retina. Moreover, the full and inner thicknesses of the retina were assessed.

RESULTS

There were significant differences in all sectors between the groups in regard to the superficial vessel density and the inner and full thicknesses of the retina. The nasal sector of the macular superficial vessel density was affected more in LHON than in NA-AION; the same with the temporal sector of the retinal thickness. There were no significant differences between the groups in the deep vessel plexus. There were no significant differences between the vasculature of the inferior and superior hemifields of the macula in all groups and no correlation with the visual function.

CONCLUSIONS

The superficial perfusion and structure of the macula assessed with OCT-A are affected both in chronic LHON and NA-AION, but more in LHON eyes, especially in the nasal and temporal sectors.

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 with Mitochondrial DNA Mutation G11778A: A Systematic Literature Review and Meta-Analysis

Background

LHON is a progressive disease with early disease onset and male predominance, usually causing devastating visual loss to patients. These systematic review and meta-analysis are aimed at summarizing epidemiology, disease onset and progression, visual recovery, risk factors, and treatment options of Leber's hereditary optic neuropathy (LHON) with mitochondrial DNA mutation G11778A from current evidence.

Methods

The PubMed database was examined from its inception date to November 2021. Data from included studies were pooled with either a fixed-effects model or a random-effects model, depending on the results of heterogeneity tests. Sensitivity analysis was conducted to test the robustness of results.

Results

A total of 41 articles were included in the systematic review for qualitative analysis, and 34 articles were included for quantitative meta-analysis. The pooled estimate of proportion of G11778A mutation among the three primary mutations of mitochondrial DNA (G11778A, G3460A, and T14484C) for LHON was 73% (95% CI: 67% and 79%), and the LHON patients with G11778A mutation included the pooled male ratio estimate of 77% (76% and 79%), the pooled age estimate of 35.3 years (33.2 years and 37.3 years), the pooled onset age estimate of 22.1 years (19.7 years and 24.6 years), the pooled visual acuity estimate of 1.4 LogMAR (1.2 LogMAR and 1.6 LogMAR), and the pooled estimate of spontaneous visual recovery rate (in either 1 eye) of 20% (15% and 27%).

Conclusions

The G11778A mutation is a prevalent mitochondrial DNA mutation accounting for over half of LHON cases with three primary mutations. Spontaneous visual recovery is rare, and no effective treatment is currently available.

Quantitative assessment of macular and circumpapillary retinal vessel density across all stages of Leber hereditary optic neuropathy using swept source optical coherence tomography angiography

PURPOSE

To investigate the macular and circumpapillary retinal microvasculature across all stages of Leber hereditary optic neuropathy (LHON) using swept source optical coherence tomography angiography (OCTA).

METHODS

This prospective, multicentre, cross-sectional, observational study analysed a total of 119 eyes of 60 patients with molecularly confirmed LHON across all stages and 120 eyes of 60 control subjects. Optical coherence tomography angiography maps centred on the fovea and optic disc were obtained to measure vessel densities (VDs) in the macular superficial (SCP) and deep (DCP) capillary plexuses, and the radial peripapillary capillary plexus (RPCP) respectively.

RESULTS

In asymptomatic eyes, only the SCP showed significant changes on average (B coefficient = -0.72, 95% CI = -1.34 to -0.10, p = 0.022) or in sectors representing the papillomacular bundle (PMB) (B coefficient = -1.17, 95% CI = -2.23 to -0.11, p = 0.031). However, in chronic eyes, the greatest magnitude of change was found in the temporal sector of the RPCP (B coefficient = -12.36, 95% CI = -14.49 to -10.23, p < 0.001). The RPCP showed the strongest correlations with visual acuity (VA, logarithm of the minimum angle of resolution; R = -0.677, p < 0.001) and structural parameters (R = 0.747, p < 0.001).

CONCLUSIONS

Retinal VD changes in the circumpapillary region of the PMB appear later than in the macula but end up being more profound and correlate better with VA and structural parameters. Further studies are needed to assess the clinical utility of retinal VDs as potential LHON biomarkers.

Mitochondrial Retinopathies

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

Late-Onset Leber's Hereditary Optic Neuropathy with Concurrent Retinal Detachment and Retrobulbar Visual Pathway Involvement

We report a case of late-onset Leber's hereditary optic neuropathy (LHON) with concurrent retinal detachment, mild retinal pigment epithelial changes, cataract and hyperintensity on fluid-attenuated inversion recovery magnetic resonance imaging affecting the entire retrobulbar visual pathway. We also documented that progression of the visual field defect correlated with retinal nerve fibre layer and ganglion cell layer-inner plexiform layer changes on optical coherence tomography. Our case provides further understanding of LHON as a disorder of the entire pre-geniculate pathways and also highlights that detailed history taking in addition to recognition of typical sequential optic disc appearance and visual field characteristics at different stages of LHON remain critical even in this era of modern imaging, autoimmune biomarkers and genetic testing.

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

Purpose

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

Methods

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

Results

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

Conclusions

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

Translational Relevance

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

Cross-Sectional Analysis of Baseline Visual Parameters in Subjects Recruited Into the RESCUE and REVERSE ND4-LHON Gene Therapy Studies

OBJECTIVE

This report presents a cross-sectional analysis of the baseline characteristics of subjects with Leber hereditary optic neuropathy enrolled in the gene therapy trials RESCUE and REVERSE, to illustrate the evolution of visual parameters over the first year after vision loss.

METHODS

RESCUE and REVERSE were 2 phase III clinical trials designed to assess the efficacy of rAAV2/2-ND4 gene therapy in ND4-LHON subjects. At enrollment, subjects had vision loss for ≤6 months in RESCUE, and between 6 and 12 months in REVERSE. Functional visual parameters (best-corrected visual acuity [BCVA], contrast sensitivity [CS], and Humphrey Visual Field [HVF]) and structural parameters assessed by spectral-domain optical coherence tomography were analyzed in both cohorts before treatment. The cross-sectional analysis of functional and anatomic parameters included the baseline values collected in all eyes at 2 different visits (Screening and Inclusion).

RESULTS

Seventy-six subjects were included in total, 39 in RESCUE and 37 in REVERSE. Mean BCVA was significantly worse in RESCUE subjects compared with REVERSE subjects (1.29 and 1.61 LogMAR respectively, P = 0.0029). Similarly, mean CS and HVF were significantly more impaired in REVERSE vs RESCUE subjects (P < 0.005). The cross-sectional analysis showed that the monthly decrease in BCVA, ganglion cell layer macular volume, and retinal nerve fiber layer thickness was much more pronounced in the first 6 months after onset (+0.24 LogMAR, -0.06 mm3, and -6.00 μm respectively) than between 6 and 12 months after onset (+0.02 LogMAR, -0.01 mm3, and -0.43 μm respectively).

CONCLUSION

LHON progresses rapidly in the first months following onset during the subacute phase, followed by relative stabilization during the dynamic phase.

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.

Intravitreal Gene Therapy vs. Natural History in Patients With Leber Hereditary Optic Neuropathy Carrying the m.11778G>A ND4 Mutation: Systematic Review and Indirect Comparison

Objective: This work aimed to compare the evolution of visual outcomes in Leber hereditary optic neuropathy (LHON) patients treated with intravitreal gene therapy to the spontaneous evolution in prior natural history (NH) studies. Design: A combined analysis of two phase three randomized, double-masked, sham-controlled studies (REVERSE and RESCUE) and their joint long-term extension trial (CLIN06) evaluated the efficacy of rAAV2/2-ND4 vs. 11 pooled NH studies used as an external control. Subjects: The LHON subjects carried the m.11778G>A ND4 mutation and were aged ≥15 years at onset of vision loss. Methods: A total of 76 subjects received a single intravitreal rAAV2/2-ND4 injection in one eye and sham injection in the fellow eye within 1 year after vision loss in REVERSE and RESCUE. Both eyes were considered as treated due to the rAAV2/2-ND4 treatment efficacy observed in the contralateral eyes. Best corrected visual acuity (BCVA) from REVERSE, RESCUE, and CLIN06 up to 4.3 years after vision loss was compared to the visual acuity of 208 NH subjects matched for age and ND4 genotype. The NH subjects were from a LHON registry (REALITY) and from 10 NH studies. A locally estimated scatterplot smoothing (LOESS), non-parametric, local regression model was used to modelize visual acuity curves over time, and linear mixed model was used for statistical inferences. Main Outcome Measures: The main outcome measure was evolution of visual acuity from 12 months after vision loss, when REVERSE and RESCUE patients had been treated with rAAV2/2-ND4. Results: The LOESS curves showed that the BCVA of the treated patients progressively improved from month 12 to 52 after vision loss. At month 48, there was a statistically and clinically relevant difference in visual acuity of -0.33 logarithm of the minimal angle of resolution (LogMAR) (16.5 ETDRS letters equivalent) in favor of treated eyes vs. NH eyes (p < 0.01). Most treated eyes (88.7%) were on-chart at month 48 as compared to 48.1% of the NH eyes (p < 0.01). The treatment effect at last observation remained statistically and clinically significant when adjusted for age and duration of follow-up (-0.32 LogMAR, p < 0.0001). Conclusions: The m.11778G>A LHON patients treated with rAAV2/2-ND4 exhibited an improvement of visual acuity over more than 4 years after vision loss to a degree not demonstrated in NH studies. Clinical Trial Registration: NCT02652767, NCT02652780, NCT03406104, and NCT03295071.

Visual Outcomes in Leber Hereditary Optic Neuropathy Patients With the m.11778G>A (MTND4) Mitochondrial DNA Mutation

BACKGROUND

Leber hereditary optic neuropathy (LHON) is a maternally inherited bilaterally blinding optic neuropathy, predominantly affecting otherwise healthy young individuals, mostly men. The visual prognosis is generally poor, with most patients worsening to at least 20/200 visual acuity. The m.11778G>A (MTND4) mitochondrial DNA mutation is the most common cause of LHON and is associated with poor outcomes and limited potential for meaningful visual recovery. Treatments for LHON are limited, and clinical trials are hampered by inadequate data regarding the natural history of visual loss and recovery. In this article, we review the current literature specifically related to visual function of LHON patients with the m.11778G>A mutation.

EVIDENCE ACQUISITION

Literature review was performed using MEDLINE through PubMed, Cochrane Reviews Library, and Orpha.net with search terms of "Leber hereditary optic neuropathy," "LHON," "ND4," "G11778A," "visual acuity," "nadir," "natural history," and "registry." All English-language, peer-reviewed publications with study cohorts of at least 5 LHON patients with the molecularly confirmed m.11778G>A mutation were included.

RESULTS

Meta-analysis of 12 retrospective and 3 prospective studies provided visual function information on 695 LHON patients with the m.11778G>A mutation, 100 (14.4%) of whom were reported to have "recovered" some vision, although definitions of "recovery" varied among studies and idebenone use could not always be excluded. When incorporating age at onset of visual loss into the analyses, and specifically addressing those patients aged 15 years or older, meaningful visual recovery occurred in 23 of 204 (11.3%) patients. A younger age at onset, especially less than 12 years, portends a better visual prognosis and a different natural history of visual loss progression and recovery than in adults.

CONCLUSIONS

The classic presentation of LHON patients with the m.11778G>A mutation of severe visual loss with rare or poor recovery from nadir still holds true for most affected individuals. Among patients 15 years and older, recovery of meaningful vision likely occurs in less than 20% of patients, irrespective of how recovery is defined, and ultimate visual acuities of better than 20/200 are rare. Adequate prospective studies with sufficient sample sizes of genotypically homogeneous untreated LHON patients stratified by age, immediately enrolled when symptomatic, followed regularly for adequate periods of time with consistent measures of visual function, and analyzed with a standard definition of visual improvement are unfortunately lacking. Future clinical trials for LHON will require more standardized reporting of the natural history of this disorder.

Resolving complexity in mitochondrial disease: Towards precision medicine

Mitochondrial diseases, caused by mutations in either the nuclear or mitochondrial genomes (mtDNA), are the most common form of inherited neurometabolic disorders. They are remarkably heterogeneous, both in their clinical presentation and genetic etiology, presenting challenges for diagnosis, clinical management and elucidation of molecular mechanism. The multifaceted nature of these diseases, compounded by the unique characteristics of mitochondrial genetics, cement their space in the field of complex disease. In this review we examine the m.3243A>G variant, one of the most prevalent mitochondrial DNA mutations, using it as an exemplar to demonstrate the challenges presented by these complex disorders. Disease caused by m.3243A>G is one of the most phenotypically diverse of all mitochondrial diseases; we outline known causes of this heterogeneity including mtDNA heteroplasmy, mtDNA copy number and nuclear genetic factors. We consider the impact that this has in the clinic, discussing the personalized management of common manifestations attributed to this pathogenic mtDNA variant, including hearing impairment, diabetes mellitus, myopathy, cardiac disease, stroke-like episodes and gastrointestinal disturbances. Future research into this complex disorder must account for this heterogeneity, benefitting from the use of large patient cohorts to build upon current clinical expertise. Through multi-disciplinary collaboration, the complexities of this mitochondrial disease can be addressed with the variety of diagnostic, prognostic, and treatment approaches that are moulded to best fit the needs of each individual patient.

Leigh syndrome with atypical cerebellar lesions

Leigh Syndrome is a neurodegenerative disorder caused by mitochondrial dysfunction, with significant phenotypic and genetic heterogeneity. It usually presents in early life, with a severe prognosis. It can be caused by more than 75 different gene mutations, of nuclear and mitochondrial origin, involving all respiratory chain complexes, with less than 25% of Leigh syndrome having mitochondrial DNA mutations. The typical pathologic hallmarks are focal, bilateral, and symmetric lesions in the basal ganglia, thalamus, cerebellum, cerebral white matter and spinal cord gray matter, usually with T2WI and FLAIR hyperintensity. The basal ganglia and thalami frequently present with a pattern of cytotoxic edema. We present one case with clinical and analytical features consistent with Leigh Syndrome, with peculiar imaging features, showing dominant cerebellar edematous changes with unexpected petechial component suggestive of microangiopathy. To our knowledge, these features are unreported and suggest the existence of microvascular lesions. Based on the reported imaging findings, we propose that Leigh Syndrome should be added to the differential diagnosis of acute cerebellitis.

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Leigh Syndrome is a neurodegenerative disorder with a severe prognosis.

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Child with dominant cerebellar findings, with reversible, topographically altering edematous changes, and unexpected petechial component.

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MRI features previously unreported, representing a new imaging presentation of the syndrome.

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Suggestion of an unknown microvascular pathophysiologic mechanism eventually related to the process of neurodegeneration.

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Proposition of Leigh Syndrome addition to the differential diagnosis of acute cerebellitis imaging features in children.

Peripapillary vessel density changes in Leber's hereditary optic neuropathy: a new biomarker

IMPORTANCE

The contribution of the microvascular supply to the pathogenesis of Leber's hereditary optic neuropathy (LHON) is poorly understood.

BACKGROUND

We aimed at measuring the peripapillary capillary vessel density (VD) using optical coherence tomography angiography (OCT-A) at different stages of LHON.

DESIGN

Prospective, cross-sectional, multicenter, observational study.

PARTICIPANTS

Twenty-two LHON patients divided in four groups: unaffected mutation carriers (LHON-u); early sub-acute stage (LHON-e); late sub-acute stage (LHON-l); chronic stage (LHON-ch).

METHODS

OCT-A scans centred on the optic disc were obtained by spectral domain OCT system.

MAIN OUTCOME MEASURES

VD, retinal nerve fibre layer (RNFL) and ganglion cell-inner plexiform layer (GC-IPL) thickness were compared between groups.

RESULTS

Significant VD changes were detected in every sector (P < 0.0001). In LHON-e, the VD was reduced in the temporal sector compared with LHON-u and in the temporal and inferotemporal sectors compared with controls. In LHON-l, VD was reduced in whole, temporal, superotemporal and inferotemporal sectors compared with LHON-u and controls. In LHON-ch, the VD was reduced in all sectors compared to the other groups. An asynchronous pattern emerged in the temporal sector with VD changes occurring earlier than RNFL thickness changes and together with GC-IPL thinning.

CONCLUSIONS AND RELEVANCE

Significant peripapillary miscrovascular changes were detected over the different stages of LHON. Studying the vascular network separately from fibres revealed that microvascular changes in the temporal sector preceded the changes of RNFL and mirrored the GC-IPL changes. Measurements of the peripapillary vascular network may become a useful biomarker to monitor the disease process, evaluate therapeutic efficacy and elucidate pathophysiology.

Incomplete penetrance in mitochondrial optic neuropathies

Incomplete penetrance characterizes the two most frequent inherited optic neuropathies, Leber's Hereditary Optic Neuropathy (LHON) and dominant optic atrophy (DOA), due to genetic errors in the mitochondrial DNA (mtDNA) and the nuclear DNA (nDNA), respectively. For LHON, compelling evidence has accumulated on the complex interplay of mtDNA haplogroups and environmental interacting factors, whereas the nDNA remains essentially non informative. However, a compensatory mechanism of activated mitochondrial biogenesis and increased mtDNA copy number, possibly driven by a permissive nDNA background, is documented in LHON; when successful it maintains unaffected the mutation carriers, but in some individuals it might be hampered by tobacco smoking or other environmental factors, resulting in disease onset. In females, mitochondrial biogenesis is promoted and maintained within the compensatory range by estrogens, partially explaining the gender bias in LHON. Concerning DOA, none of the above mechanisms has been fully explored, thus mtDNA haplogroups, environmental factors such as tobacco and alcohol, and further nDNA variants may all participate as protective factors or, on the contrary, favor disease expression and severity. Next generation sequencing, complemented by transcriptomics and proteomics, may provide some answers in the next future, even if the multifactorial model that seems to apply to incomplete penetrance in mitochondrial optic neuropathies remains problematic, and careful stratification of patients will play a key role for data interpretation. The deep understanding of which factors impinge on incomplete penetrance may shed light on the pathogenic mechanisms leading to optic nerve atrophy, on their possible compensation and, thus, on development of therapeutic strategies.

Mitochondrial vasculopathy

Mitochondrial disorders (MIDs) are usually multisystem disorders (mitochondrial multiorgan disorder syndrome) either on from onset or starting at a point during the disease course. Most frequently affected tissues are those with a high oxygen demand such as the central nervous system, the muscle, endocrine glands, or the myocardium. Recently, it has been shown that rarely also the arteries may be affected (mitochondrial arteriopathy). This review focuses on the type, diagnosis, and treatment of mitochondrial vasculopathy in MID patients. A literature search using appropriate search terms was carried out. Mitochondrial vasculopathy manifests as either microangiopathy or macroangiopathy. Clinical manifestations of mitochondrial microangiopathy include leukoencephalopathy, migraine-like headache, stroke-like episodes, or peripheral retinopathy. Mitochondrial macroangiopathy manifests as atherosclerosis, ectasia of arteries, aneurysm formation, dissection, or spontaneous rupture of arteries. The diagnosis relies on the documentation and confirmation of the mitochondrial metabolic defect or the genetic cause after exclusion of non-MID causes. Treatment is not at variance compared to treatment of vasculopathy due to non-MID causes. Mitochondrial vasculopathy exists and manifests as micro- or macroangiopathy. Diagnosing mitochondrial vasculopathy is crucial since appropriate treatment may prevent from severe complications.

Genetics of Primary Inherited Disorders of the Optic Nerve: Clinical Applications

Inherited disorders of the optic nerve significantly impact vision in children and adults. The optic nerve disorders most commonly encountered clinically are glaucoma and primary optic neuropathy including Leber's hereditary optic neuropathy (LHON) and autosomal dominant or Kjer's optic atrophy. Current knowledge of the genetics of optic neuropathy and glaucoma makes it possible to test for mutations in disease-causing genes allowing for presymptomatic testing and risk assessment, and recent advances have revealed important disease mechanisms that may suggest potential therapeutic targets. In this perspective, we describe the current approaches and limitations to genetic testing for these disorders and provide an update on the development of gene-based therapies.

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.

Leber hereditary optic neuropathy in the population of Serbia

BACKGROUND

Leber hereditary optic neuropathy (LHON) is the most common mitochondrial disorder. However, few countries have published their population-based findings related to this multisystemic disease.

THE AIM

In order to get a better insight into the epidemiological and clinical picture of this maternally inherited disorder, we performed the first population-based clinical and molecular-genetic study of LHON in the Serbian population.

METHODS

Prospective study included patients who were diagnosed with LHON after detailed medical examination and molecular-genetic confirmation.

RESULTS

We identified 41 individuals from 12 genealogically unrelated families, carrying one of the three "primary" mitochondrial (mt) DNA point mutations associated with LHON. Fourteen of them were clinically affected, giving a minimum point prevalence of 1.9 per 1,000,000. The minimum point prevalence for mtDNA LHON mutations was 5.2 per 1,000,000. Male to female ratio was 6:1. Only one affected patient harboured mutant mtDNA in heteroplasmic condition. All patients were presented with common clinical findings.

CONCLUSION

We observed significantly lower prevalence and higher gender ratio than expected. However, frequencies of primary mutations, incidence of heteroplasmy and clinical findings are in accordance with other studies in Caucasoid populations. Our results might be a consequence of poor recognition and misdiagnosis due to lack of diagnostic possibilities of the entity in different region of our country or less likely be in part due to specific haplotype background of Serbian population which should be further investigated.

Retinal ganglion cell dysfunction in asymptomatic G11778A: Leber hereditary optic neuropathy

PURPOSE

To report the serial evaluation of asymptomatic eyes of subjects with mutated G11778A mitochondrial DNA.

METHODS

Forty-five asymptomatic G11778A Leber hereditary optic neuropathy (LHON) carriers and two patients with the mutation who developed unilateral visual loss underwent testing that included visual acuity, automated visual field, pattern electroretinogram (PERG), and spectral-domain optical coherence tomography every 6 months between September 2008 and March 2012.

RESULTS

Visual acuity, visual fields, and retinal nerve fiber layer thickness remained stable within the normal range. Mean PERG amplitudes of carriers dropped progressively by ∼ 40% from baseline to 36 months. In addition, comparisons with the fellow eyes of patients with unilateral optic neuritis revealed a 3.4 ETDRS (Early Treatment Diabetic Retinopathy Study) letter loss in the LHON carriers. A single carrier developed visual loss, with PERG amplitudes dropping by half. In one of two LHON cases who presented with unilateral visual loss, visual acuity in the asymptomatic eye was ∼ 20/40 at baseline. The PERG amplitude of this eye was reduced to ∼ 30% of normal. Six months later, his visual acuity had dropped to ∼ 20/500. A second patient who was ∼ 20/20 and had a visual field defect in the asymptomatic eye at baseline remained at this level for the 18 months of follow-up. His PERG amplitudes were similar to those of asymptomatic carriers, with 0.78 μV at baseline that did not decline with follow-up.

CONCLUSIONS

Declines of the PERG amplitude suggest subclinical retinal ganglion cell dysfunction in asymptomatic G11778A subjects, which is progressive.

Efficient mitochondrial biogenesis drives incomplete penetrance in Leber's hereditary optic neuropathy

Leber's hereditary optic neuropathy is a maternally inherited blinding disease caused as a result of homoplasmic point mutations in complex I subunit genes of mitochondrial DNA. It is characterized by incomplete penetrance, as only some mutation carriers become affected. Thus, the mitochondrial DNA mutation is necessary but not sufficient to cause optic neuropathy. Environmental triggers and genetic modifying factors have been considered to explain its variable penetrance. We measured the mitochondrial DNA copy number and mitochondrial mass indicators in blood cells from affected and carrier individuals, screening three large pedigrees and 39 independently collected smaller families with Leber's hereditary optic neuropathy, as well as muscle biopsies and cells isolated by laser capturing from post-mortem specimens of retina and optic nerves, the latter being the disease targets. We show that unaffected mutation carriers have a significantly higher mitochondrial DNA copy number and mitochondrial mass compared with their affected relatives and control individuals. Comparative studies of fibroblasts from affected, carriers and controls, under different paradigms of metabolic demand, show that carriers display the highest capacity for activating mitochondrial biogenesis. Therefore we postulate that the increased mitochondrial biogenesis in carriers may overcome some of the pathogenic effect of mitochondrial DNA mutations. Screening of a few selected genetic variants in candidate genes involved in mitochondrial biogenesis failed to reveal any significant association. Our study provides a valuable mechanism to explain variability of penetrance in Leber's hereditary optic neuropathy and clues for high throughput genetic screening to identify the nuclear modifying gene(s), opening an avenue to develop predictive genetic tests on disease risk and therapeutic strategies.

Mitochondrial optic neuropathies: our travels from bench to bedside and back again

The standard scientific method requires that you make an interesting observation, generate a hypothesis and then design an experiment to test the hypothesis. In ophthalmology, as in most fields of medicine, the observations and hypotheses tend to have more degrees of freedom, and the interpretation of experiments is also more complicated and often indeterminate. But sometimes it works out, going back and forth from bench to bedside to bench, in reiterative cycles. A successful example of alternating bench and bedside studies was presented (AAS) at the 2012 Alper Memorial given at the Washington Hospital Medical Center, illustrating a series of questions and investigations that pertain to mitochondrial optic neuropathies, beginning two decades ago, before the concept of mitochondrial optic neuropathies had much meaning. Basic science questions are often best answered by that extraordinary experiment of nature that we call clinical disease, and clinical questions are often best tested in the laboratory.

Neurologic disorders due to mitochondrial DNA mutations

The mitochondrial DNA (mtDNA) is a compact genome inherited through the maternal lineage. Mutations in mtDNA lead to many of the earliest identified syndromic mitochondrial diseases and display a diverse range of age of onset, symptoms, and outcomes-from isolated childhood onset vision or hearing loss to a multisystemic neurodegenerative disorder with strokes, neuropathy, ophthalmoparesis, and epilepsy beginning at any age. As a heterogeneous group, mitochondrial diseases represent one of the most common metabolic disorders in children and adults, frequently seen by both pediatric and adult specialists. Although the myriad of diseases can make diagnosis seems daunting, the need for extensive supportive care and treatment (the latter for at least a select few mitochondrial disorders) and a rapid and accurate recognition of these disorders is necessary. Here, we provide a review of the most common mitochondrial disease syndromes due to mtDNA mutations.

Secondary post-geniculate involvement in Leber's hereditary optic neuropathy

Leber’s hereditary optic neuropathy (LHON) is characterized by retinal ganglion cell (RGC) degeneration with the preferential involvement of those forming the papillomacular bundle. The optic nerve is considered the main pathological target for LHON. Our aim was to investigate the possible involvement of the post-geniculate visual pathway in LHON patients. We used diffusion-weighted imaging for in vivo evaluation. Mean diffusivity maps from 22 LHON visually impaired, 11 unaffected LHON mutation carriers and 22 healthy subjects were generated and compared at level of optic radiation (OR). Prefrontal and cerebellar white matter were also analyzed as internal controls. Furthermore, we studied the optic nerve and the lateral geniculate nucleus (LGN) in post-mortem specimens obtained from a severe case of LHON compared to an age-matched control. Mean diffusivity values of affected patients were higher than unaffected mutation carriers (P<0.05) and healthy subjects (P<0.01) in OR and not in the other brain regions. Increased OR diffusivity was associated with both disease duration (B = 0.002; P<0.05) and lack of recovery of visual acuity (B = 0.060; P<0.01). Post-mortem investigation detected atrophy (41.9% decrease of neuron soma size in the magnocellular layers and 44.7% decrease in the parvocellular layers) and, to a lesser extent, degeneration (28.5% decrease of neuron density in the magnocellular layers and 28.7% decrease in the parvocellular layers) in the LHON LGN associated with extremely severe axonal loss (99%) in the optic nerve. The post-geniculate involvement in LHON patients is a downstream post-synaptic secondary phenomenon, reflecting de-afferentation rather than a primary neurodegeneration due to mitochondrial dysfunction of LGN neurons.

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.

Neuron-specific enolase is elevated in asymptomatic carriers of Leber's hereditary optic neuropathy

PURPOSE

Neuron-specific enolase (NSE) is a biomarker for neuronal stress. Leber's hereditary optic neuropathy (LHON) is a mitochondrial disease affecting retinal ganglion cells (RGC). These RGCs and their axons in the retinal nerve fiber layer (RNFL) and optic nerve head may show subclinical pathology in unaffected mutation carriers, or undergo cell death in affected patients. We hypothesize that increased levels of blood NSE may characterize LHON carriers as a biomarker of ongoing RGC stress.

METHODS

Serum was obtained from 74 members of a Brazilian pedigree with LHON carrying the homoplasmic 11778/ND4 mitochondrial DNA mutation. Classified by symptoms and psychophysical metrics, 46/74 patients were unaffected mutation "carriers," 14/74 were "affected," and 14/74 were "off-pedigree" controls. Serum NSE levels were determined by ELISA specific for the γ subunit of NSE.

RESULTS

Serum NSE concentrations in carriers (27.17 ± 39.82 μg/L) were significantly higher than affected (5.66 ± 4.19 μg/L; P = 0.050) and off-pedigree controls (6.20 ± 2.35 μg/L; P = 0.047). Of the 14/46 (30.4 %) carriers with significantly elevated NSE levels (mean = 75.8 ± 42.3 μg/L), 9/14 (64.3%) were male. Furthermore, NSE levels were nearly three times greater in asymptomatic male carriers (40.65 ± 51.21 μg/L) than in asymptomatic female carriers (15.85 ± 22.27 μg/L; P = 0.034).

CONCLUSIONS

Serum NSE levels are higher in LHON carriers compared with affected and off-pedigree individuals. A subgroup of mostly male carriers had significantly elevated serum NSE levels. Thus, male carriers are at higher risk for LHON-related neuronal stress.

Primary mitochondrial arteriopathy

AIM

Whether arteries are affected in mitochondrial disorders (MIDs) was under debate for years but meanwhile there are strong indications that large and small arteries are primarily or secondarily affected in MIDs.

DATA SYNTHESIS

When reviewing the literature for appropriate studies it turned out that vascular involvement in MIDs includes primary or secondary micro- or macroangiopathy of the cerebral, cervical, and retinal arteries, the aorta, the iliac arteries, the brachial arteries, or the muscular arteries. Arteriopathy in MIDs manifests as atherosclerosis, stenosis, occlusion, dissection, ectasia, aneurysm formation, or arteriovenous malformation. Direct evidence for primary cerebral microangiopathy comes from histological studies and indirect evidence from imaging and perfusion studies of the brain. Microangiopathy of the retina is highly prevalent in Leber's hereditary optic neuropathy. Macroangiopathy of the carotid arteries may be complicated by stroke. Arteriopathy of the aorta may result in ectasia, aneurysm formation, or even rupture. Further evidence for arteriopathy in MIDs comes from the frequent association of migraine with MIDs and the occurrence of premature atherosclerosis in MID patients without classical risk factors.

CONCLUSIONS

Mitochondrial arteriopathy most frequently concerns the cerebral arteries and may result from the underlying metabolic defect or secondary from associated vascular risk factors. Vascular involvement in MIDs has a strong impact on the prognosis and outcome of these patients.

Axonal degeneration in peripheral nerves in a case of Leber hereditary optic neuropathy

BACKGROUND

Leber hereditary optic neuropathy (LHON) is a mitochondrial DNA (mtDNA) genetic disorder characterized by profound bilateral loss of central vision due to selective loss of retinal ganglion cells. Most patients with LHON do not have complaints related to the peripheral nervous system. We investigated possible qualitative and quantitative histological changes in the peripheral nerve of a patient with LHON as compared to normal controls.

METHODS

Brachial plexus specimens were obtained at necropsy from a patient with LHON carrying the 3460/ND1 mtDNA mutation and age-matched controls without known history of neurological disease. The nerves were evaluated by light microscope coupled to a digital camera-based morphometric analysis and electron microscopy.

RESULTS

Extensive axonal degeneration of the large heavily myelinated fibers was found in the brachial plexus from the patient with LHON. In LHON nerve fascicles, we counted over 10 times as many degenerated profiles as found in the control nerve fascicles.

CONCLUSIONS

Microscopic examination of the brachial plexus in the patient with LHON clearly demonstrated a significant pattern of neurodegeneration. Our study suggests that peripheral neuropathy may be a subclinical feature associated with LHON.

Mitochondrial-nuclear epistasis: implications for human aging and longevity

There is substantial evidence that mitochondria are involved in the aging process. Mitochondrial function requires the coordinated expression of hundreds of nuclear genes and a few dozen mitochondrial genes, many of which have been associated with either extended or shortened life span. Impaired mitochondrial function resulting from mtDNA and nuclear DNA variation is likely to contribute to an imbalance in cellular energy homeostasis, increased vulnerability to oxidative stress, and an increased rate of cellular senescence and aging. The complex genetic architecture of mitochondria suggests that there may be an equally complex set of gene interactions (epistases) involving genetic variation in the nuclear and mitochondrial genomes. Results from Drosophila suggest that the effects of mtDNA haplotypes on longevity vary among different nuclear allelic backgrounds, which could account for the inconsistent associations that have been observed between mitochondrial DNA (mtDNA) haplogroups and survival in humans. A diversity of pathways may influence the way mitochondria and nuclear-mitochondrial interactions modulate longevity, including: oxidative phosphorylation; mitochondrial uncoupling; antioxidant defenses; mitochondrial fission and fusion; and sirtuin regulation of mitochondrial genes. We hypothesize that aging and longevity, as complex traits having a significant genetic component, are likely to be controlled by nuclear gene variants interacting with both inherited and somatic mtDNA variability.

Visual fields in neuro-ophthalmology

Visual field assessment is important in the evaluation of lesions involving the visual pathways and should be performed at baseline and periodically in the follow-up. Standard automated perimetry has been shown to be adequate in neuro-ophthalmic practise and is now the technique of choice for a majority of practitioners. Goldman kinetic visual fields are useful for patients with severe visual and neurologic deficits and patients with peripheral visual field defects. Visual fields are useful in monitoring progression or recurrence of disease and guide treatment for conditions such as idiopathic intracranial hypertension (IIH), optic neuropathy from multiple sclerosis, pituitary adenomas, and other sellar lesions. They are used as screening tools for toxic optic neuropathy from medications such as ethambutol and vigabatrin. Visual field defects can adversely affect activities of daily living such as personal hygiene, reading, and driving and should be taken into consideration when planning rehabilitation strategies. Visual field testing must be performed in all patients with lesions of the visual pathway.

Leber's hereditary optic neuropathy: clinical and molecular profile of a Brazilian sample

PURPOSE

The aim of this study was to describe clinical features and search for primary mitochondrial DNA (mtDNA) mutations in 13 unrelated Brazilian patients with Leber's hereditary optic neuropathy (LHON).

METHODS

Analysis of the G11778A, G3460A, and T14484C mutations was done by polymerase chain reaction and restriction fragment length polymorphism, and mutations were confirmed by direct sequencing. Mean age of onset was 24.5 years and all cases were bilateral.

RESULTS

Sex ratio (12M:1F) and frequency of simultaneous involvement (9/13) were higher than in other studies. In nine cases there was familial recurrence: 24 male and two female relatives. Ten patients had a mutation: G11778A in six, T14484C in three and one G3460A. The frequency of patients bearing a primary mutation was lower than that described in multicentric studies but similar to that observed among Asians. A higher frequency of the T14484C mutation was detected.

CONCLUSIONS

The contribution of Amerindians and Africans to the Brazilian mtDNA pool may account for differences in the type and frequency of primary LHON mutations.

Inherited mitochondrial optic neuropathies

Leber hereditary optic neuropathy (LHON) and autosomal dominant optic atrophy (DOA) are the two most common inherited optic neuropathies and they result in significant visual morbidity among young adults. Both disorders are the result of mitochondrial dysfunction: LHON from primary mitochondrial DNA (mtDNA) mutations affecting the respiratory chain complexes; and the majority of DOA families have mutations in the OPA1 gene, which codes for an inner mitochondrial membrane protein critical for mtDNA maintenance and oxidative phosphorylation. Additional genetic and environmental factors modulate the penetrance of LHON, and the same is likely to be the case for DOA which has a markedly variable clinical phenotype. The selective vulnerability of retinal ganglion cells (RGCs) is a key pathological feature and understanding the fundamental mechanisms that underlie RGC loss in these disorders is a prerequisite for the development of effective therapeutic strategies which are currently limited.

Evidence for a novel x-linked modifier locus for leber hereditary optic neuropathy

Leber Hereditary Optic Neuropathy (LHON) is a maternally inherited blinding disease caused by missense mutations in the mitochondrial DNA (mtDNA). However, incomplete penetrance and a predominance of male patients presenting with vision loss suggest that modifying factors play an important role in the development of the disease. Evidence from several studies suggests that both nuclear modifier genes and environmental factors may be necessary to trigger the optic neuropathy in individuals harboring an LHON-causing mtDNA mutation. Recently, an optic neuropathy susceptibility locus at Xp21-Xq21 has been reported. In this study, we performed X-chromosomal linkage analysis in a large Brazilian family harboring a homoplasmic G11778A mtDNA mutation on a haplogroup J background. We report the identification of a novel LHON susceptibility locus on chromosome Xq25-27.2, with multipoint non-parametric linkage scores of > 5.00 (P = 0.005) and a maximum two-point non-parametric linkage score of 10.12, (P = 0.003) for marker DXS984 (Xq27.1). These results suggest genetic heterogeneity for X-linked modifiers of LHON.

Selection against pathogenic mtDNA mutations in a stem cell population leads to the loss of the 3243A-->G mutation in blood

The mutation 3243A-->G is the most common heteroplasmic pathogenic mitochondrial DNA (mtDNA) mutation in humans, but it is not understood why the proportion of this mutation decreases in blood during life. Changing levels of mtDNA heteroplasmy are fundamentally related to the pathophysiology of the mitochondrial disease and correlate with clinical progression. To understand this process, we simulated the segregation of mtDNA in hematopoietic stem cells and leukocyte precursors. Our observations show that the percentage of mutant mtDNA in blood decreases exponentially over time. This is consistent with the existence of a selective process acting at the stem cell level and explains why the level of mutant mtDNA in blood is almost invariably lower than in nondividing (postmitotic) tissues such as skeletal muscle. By using this approach, we derived a formula from human data to correct for the change in heteroplasmy over time. A comparison of age-corrected blood heteroplasmy levels with skeletal muscle, an embryologically distinct postmitotic tissue, provides independent confirmation of the model. These findings indicate that selection against pathogenic mtDNA mutations occurs in a stem cell population.

Minocycline, a possible neuroprotective agent in Leber’s hereditary optic neuropathy (LHON): Studies of cybrid cells bearing 11778 mutation

Leber's hereditary optic neuropathy (LHON) is a retinal neurodegenerative disorder caused by mitochondrial DNA point mutations. Complex I of the respiratory chain affected by the mutation results in a decrease in ATP and an increase of reactive oxygen species production. Evaluating the efficacy of minocycline in LHON, the drug increased the survival of cybrid cells in contrast to the parental cells after thapsigargin-induced calcium overload. Similar protection was observed by treatment with cyclosporine A, a blocker of the mitochondrial permeability transition pore (mPTP). Ratiometric Ca(2+) imaging reveals that acetylcholine/thapsigargin triggered elevation of the cytosolic calcium concentration is alleviated by minocycline and cyclosporine A. The mitochondrial membrane potential of LHON cybrids was significantly conserved and the active-caspase-3/procaspase-3 ratio was decreased in both treatments. Our observations show that minocycline inhibits permeability transition induced by thapsigargin in addition to its antioxidant effects. In relation with its high safety profile, these results would suggest minocycline as a promising neuroprotective agent in LHON.

Clinical expression of Leber hereditary optic neuropathy is affected by the mitochondrial DNA-haplogroup background

Leber hereditary optic neuropathy (LHON) is due primarily to one of three common point mutations of mitochondrial DNA (mtDNA), but the incomplete penetrance implicates additional genetic or environmental factors in the pathophysiology of the disorder. Both the 11778G-->A and 14484T-->C LHON mutations are preferentially found on a specific mtDNA genetic background, but 3460G-->A is not. However, there is no clear evidence that any background influences clinical penetrance in any of these mutations. By studying 3,613 subjects from 159 LHON-affected pedigrees, we show that the risk of visual failure is greater when the 11778G-->A or 14484T-->C mutations are present in specific subgroups of haplogroup J (J2 for 11778G-->A and J1 for 14484T-->C) and when the 3460G-->A mutation is present in haplogroup K. By contrast, the risk of visual failure is significantly less when 11778G-->A occurs in haplogroup H. Substitutions on MTCYB provide an explanation for these findings, which demonstrate that common genetic variants have a marked effect on the expression of an ostensibly monogenic mtDNA disorder.

Evaluation of optic nerve head configuration in various types of optic neuropathy with Heidelberg Retina Tomograph

PURPOSE

To test whether Heidelberg Retina Tomograph (HRT) is applicable to assess the optic nerve head (ONH) configuration of the atrophic phase of non-glaucomatous optic neuropathy when a default set of the reference plane is used.

METHODS

Ten eyes with non-arteritic anterior ischaemic optic neuropathy (NAION), 17 eyes with Leber's hereditary optic neuropathy (LHON), 40 eyes with compressive optic neuropathy (CON) owing to chiasmal tumour, and 241 eyes of control individuals were examined with HRT using the default reference plane. The global values of HRT parameters were evaluated among the groups of patients and controls. The sectoral measurements of the eyes with LHON and CON were compared with controls. To eliminate the influence of disc size and age on HRT measurements, eyes with disc area- and age-matched normal controls were used for comparison with eyes with NAION and LHON.

RESULTS

Cup parameters in eyes with NAION were similar to those in controls. The retinal nerve fibre layer (RNFL) thickness was significantly thinner in eyes with NAION than that of controls. The eyes with LHON had significantly larger cup parameters, smaller rim volume, and thinner mean RNFL thickness than controls. Eyes with CON had significantly larger rim area and smaller cup parameters but similar RNFL thickness compared with controls.

CONCLUSIONS

When the default reference plane is used, HRT can measure the ONH configuration in eyes with NAION and LHON as expected. However, caution must be made to interpret the parameters obtained from the eyes with CON.

Prevalence of mitochondrial DNA haplogroups in an Australian population

Mitochondrial DNA (mtDNA) haplogroups are 'neutral polymorphisms' in the mtDNA genome, which have accumulated and persisted along maternal lineages as the human population has migrated worldwide. Three ethnically distinct lineages of human mtDNA populations have been identified: European, characterized by nine haplogroups H, I, J, K, T, U, V, W and X; African, characterized by superhaplogroup L and Asian, characterized by superhaplogroup M. We studied the prevalence of mtDNA haplogroups in participants of the Blue Mountains Eye Study, a large population-based survey of vision conducted between 1991 and 2000 of non-institutionalized permanent residents aged 49 years or older from two suburban postcode areas, west of Sydney, Australia. Total DNA isolated from either hair follicles or blood was available for 3377 of the 3509 participants (96.2%) to determine mtDNA haplogroups by polymerase chain reaction/restriction fragment length polymorphism analysis. Approximately 94.2% of samples could be assigned to one of the nine major European haplogroups, whereas a further 1.2% included the African (L) and Asian (M) superhaplogroups. The five principal haplogroups represented were H (42.9%), U (14.1%), J (10.7%), T (9.2%) and K (8.1%), which together included 85% of this population.

Optometrists as key providers in the prevention and early detection of malignancies

Optometrists have become active in many aspects of primary health care. Opportunities exist for optometrists to join other health care providers in the fight against cancer. The purpose of this article is to review information about cancer epidemiology, describe cancer screening guidelines, and to provide examples of ways for optometrists to become involved in promoting goals for reducing cancer risk and increasing the early detection of cancer. In addition to diagnosing ocular cancers and metastases to the eye and orbital region, optometrists may provide cancer information as part of their case history, provide positive health messages to reduce cancer risk factors, and directly observe signs of skin cancer.