Leber hereditary optic neuropathy — Historical report in comparison with the current knowledge

Childhood-Onset Leber Hereditary Optic Neuropathy: Particular Features

Background

Leber hereditary optic neuropathy (LHON) is an optic neuropathy of mitochondrial inheritance. Childhood-onset disease is relatively rare and there are limited data on this important patient subgroup.

Case Presentation

We present 3 particular presentations of LHON. Patient 1 was an 8-year-old boy admitted to the emergency department reporting a progressive bilateral visual loss and intermittent headaches. Neuro-ophthalmological examination revealed a bilateral pseudopapilledema. Lumbar puncture identified intracranial hypertension and the brain and orbits magnetic resonance imaging showed T2 hyperintensity in the posterior region of the left optic nerve and the optic chiasm. Patient 2 was a 12-year-old boy admitted to the emergency department reporting painless, progressive central vision loss in the right eye. Fundus examination revealed a hyperemic disc and vascular network papillary and peripapillary vascular microdilations. Three months later, the left eye presented visual loss. Patient 3 was a 6-year-old female child referred to the neuro-ophthalmology specialist due to painless central visual loss in both eyes. Her BCVA was 1/10 and counting fingers in right and left eye, respectively, and fundus examination revealed a pallor optic disc in the temporal sector.

Discussion

The phenotype of childhood-onset disease may present itself distinct from classical adult-onset LHON. The absence of classical clinical features could lead to initial misdiagnosis. There should exist a high index of suspicion in children presenting unexplained subnormal vision in order to avoid potential diagnostic delays.

Mitochondrial genome variation in male LHON patients with the m.11778G > A mutation

Leber hereditary optic neuropathy (LHON) is a mitochondrial disorder with symptoms limited to a single tissue, optic nerve, resulting in vision loss. In the majority of cases it is caused by one of three point mutations in mitochondrial DNA (mtDNA) but their presence is not sufficient for disease development, since ~50% of men and ~10% women who carry them are affected. Thus additional modifying factors must exist. In this study, we use next generation sequencing to investigate the role of whole mtDNA variation in male Polish patients with LHON and m.11778G > A, the most frequent LHON mutation. We present a possible association between mtDNA haplogroup K and variants in its background, a combination of m.3480A > G, m.9055G > A, m.11299 T > C and m.14167C > T, and LHON mutation. These variants may have a negative effect on m.11778G > A increasing its penetrance and the risk of LHON in the Polish population. Surprisingly, we did not observe associations previously reported for m.11778G > A and LHON in European populations, particularly for haplogroup J as a risk factor, implying that mtDNA variation is much more complex. Our results indicate possible contribution of novel combination of mtDNA genetic factors to the LHON phenotype.

Discovery of Novel 2-Aniline-1,4-naphthoquinones as Potential New Drug Treatment for Leber's Hereditary Optic Neuropathy (LHON)

Leber's hereditary optic neuropathy (LHON) is a rare genetic mitochondrial disease and the primary cause of chronic visual impairment for at least 1 in 10 000 individuals in the U.K. Treatment options remain limited, with only a few drug candidates and therapeutic approaches, either approved or in development. Recently, idebenone has been investigated as drug therapy in the treatment of LHON, although evidence for the efficacy of idebenone is limited in the literature. NAD(P)H:quinone oxidoreductase 1 (NQO1) and mitochondrial complex III were identified as the major enzymes involved in idebenone activity. Based on this mode of action, computer-aided techniques and structure-activity relationship (SAR) optimization studies led to the discovery of a series naphthoquinone-related small molecules, with comparable adenosine 5'-triphosphate (ATP) rescue activity to idebenone. Among these, three compounds showed activity in the nanomolar range and one, 2-((4-fluoro-3-(trifluoromethyl)phenyl)amino)-3-(methylthio)naphthalene-1,3-dione (1), demonstrated significantly higher potency ex vivo, and significantly lower cytotoxicity, than idebenone.

Identification of an ND4 Mutation in Leber Hereditary Optic Neuropathy

SIGNIFICANCE

We identified a missense mutation, m.11778G>A (p.R340H), in the mitochondrially encoded NADH dehydrogenase 4 gene (ND4) in eight patients and three asymptomatic carriers, even though the incidence of this has been considered low in Chinese population. These results have implications for the families' genetic counseling and clinical management.

PURPOSE

Leber hereditary optic neuropathy (LHON OMIM 535000) is one of the most common inherited optic neuropathies. The aim of this study was to identify the genetic cause in two Han Chinese families with LHON.

METHODS

We used Sanger sequencing to identify the genetic cause of two Han Chinese families from Hunan, China, with LHON.

RESULTS

The patients in these two families presented with typical LHON, with male patients experiencing more severe phenotypes. A missense mutation, m.11778G>A (p.R340H), in the ND4 gene was identified in eight patients and three asymptomatic carriers, even though the incidence of this has been considered low in Chinese population.

CONCLUSIONS

Eight of 11 family members (72.7%) manifested some vision loss, which is far higher percentage than reported in other studies. The variant is predicted to be the disease-causing mutation and results in seriously abnormal function of complex I subunits of the mitochondrial respiratory chain. These results have implications for the families' genetic counseling and clinical management and help to develop new LHON target-gene therapy strategies.

Mother's curse neutralizes natural selection against a human genetic disease over three centuries

According to evolutionary theory, mitochondria could be poisoned gifts that mothers transmit to their sons. This is because mutations harmful to males are expected to accumulate in the mitochondrial genome, the so-called 'mother's curse'. However, the contribution of the mother's curse to the mutation load in nature remains largely unknown and hard to predict, because compensatory mechanisms could impede the spread of deleterious mitochondria. Here we provide evidence for the mother's curse in action over 290 years in a human population. We studied a mutation causing Leber's hereditary optical neuropathy, a disease with male-biased prevalence and which has long been suspected to be maintained in populations by the mother's curse. Male carriers showed a low fitness relative to non-carriers and to females, mostly explained by their high rate of infant mortality. Despite poor male fitness, selection analysis predicted a slight (albeit non-significant) increase in frequency, which sharply contrasts with the 35.5% per-generation decrease predicted if mitochondrial DNA transmission had been through males instead of females. Our results are therefore even suggestive of positive selection through the female line that may exacerbate effects of the mother's curse. This study supports a contribution of the mother's curse to the reduction of male lifespan, uncovering a large fitness effect associated with a single mitochondrial variant.

Genetic and Clinical Analyses of DOA and LHON in 304 Chinese Patients with Suspected Childhood-Onset Hereditary Optic Neuropathy

Leber hereditary optic neuropathy (LHON) and dominant optic atrophy (DOA), the most common forms of hereditary optic neuropathy, are easily confused, and it is difficult to distinguish one from the other in the clinic, especially in young children. The present study was designed to survey the mutation spectrum of common pathogenic genes (OPA1, OPA3 and mtDNA genes) and to analyze the genotype-phenotype characteristics of Chinese patients with suspected childhood-onset hereditary optic neuropathy. Genomic DNA and clinical data were collected from 304 unrelated Chinese probands with suspected hereditary optic neuropathy with an age of onset below 14 years. Sanger sequencing was used to screen variants in the coding and adjacent regions of OPA1, OPA3 and the three primary LHON-related mutation sites in mitochondrial DNA (mtDNA) (m.3460G>A, m.11778G>A and m.14484T>C). All patients underwent a complete ophthalmic examination and were compared with age-matched controls. We identified 89/304 (29.3%) primary mtDNA mutations related to LHON in 304 probands, including 76 mutations at m.11778 (76/89, 85.4% of all mtDNA mutations), four at m.3460 (4/89, 4.5%) and nine at m.14484 (9/89, 10.1%). This result was similar to the mutation frequency among Chinese patients with LHON of any age. Screening of OPA1 revealed 23 pathogenic variants, including 11 novel and 12 known pathogenic mutations. This study expanded the OPA1 mutation spectrum, and our results showed that OPA1 mutation is another common cause of childhood-onset hereditary optic neuropathy in Chinese pediatric patients, especially those with disease onset during preschool age.

Leber Hereditary Optic Neuropathy: Bringing the Lab to the Clinic

Leber hereditary optic neuropathy (LHON) was the first clinically characterized mitochondrial disorder. Since its first description in 1871, much has been discovered regarding the genetics and pathophysiology of the disease. This has enabled the development of in vitro cell and animal models that can be used to try to determine not only the effects of the genetic mutation upon the clinical phenotype but to also test potential novel therapies. Treatments for LHON have ranged from vitamins and minerals to immunosuppressants and, more recently, targeted gene therapy. This article reviews the pathophysiology and clinical features of LHON with a focus on translational research.

Gene-Based Therapies for Leber Hereditary Optic Neuropathy. Hype or Hope?

Leber hereditary optic neuropathy has now joined Leber congenital amaurosis in the list of genetic eye diseases undergoing gene therapy clinical trials. Although a dramatic response to treatment would be welcome, a minor improvement in vision is a major challenge in efficacy assessment, given this may occur spontaneously as part of the natural history of minor recovery in some patients. Thus, we must await the outcome of adequately powered clinical trials to know if the treatment is effective, particularly given the likely high cost of such therapeutic interventions in the future. We need global cooperation to ensure that the most suitable patients are enrolled in these trials and that support is provided for participants who need to travel from the Asia-Pacific region to Europe or North America if there are no local arms of these trials.