The unique characteristics of Thai Leber hereditary optic neuropathy: analysis of 30 G11778A pedigrees

The epidemiology and mutation types of Leber's hereditary optic neuropathy in Thailand

PURPOSE

Leber's hereditary optic neuropathy (LHON), the most common mitochondrial optic neuropathy, causes visual loss, especially in young adults. Due to the absence of epidemiological data in Southeast Asia, we aimed to determine Thai LHON patients' characteristics (demographic data, mutation types, and prognoses) as the first study in this region.

METHODS

This retrospective chart review enrolled all Thai LHON patients confirmed by three mitochondrial DNA mutations (G11778A, T14484C, and G3460A) between January 1997 and December 2016. Patients with more than one year of follow-up were included in a visual progression analysis. The Mann-Whitney U-test was applied to compare groups, and prognosis-associated factors were analysed with the generalized estimating equation.

RESULTS

In all, 229 patients were enrolled, with only nineteen females. Most mutations were of the G11778A type (91%), with T14484C accounting for the remainder. The age at onset of G11778A (21.9 years; interquartile range [IQR] 14.9, 33.5) was younger than that of T14484C (33.0 years; IQR 19.4, 37.5). Of 45 patients, the T14484C group demonstrated good vision recovery, whereas the G11778A group did not improve (difference in logMAR -0.7 and IQR -1.5, -0.2 versus logMAR 0.0 and IQR -0.3, 0.2, respectively; P value .001). The G11778A mutation, male, and older age were related to poor prognoses.

CONCLUSIONS

The leading mutation in Thai LHON patients is the G11778A missense, followed by T14484C, while G3460A was not detected. The vast majority of patients were young adult males. The G11778A mutation, older age, and male gender are associated with poor vision outcomes. Key messageThe G11778A missense mutation is the most common among Thai LHON patients, followed by T14484C, while G3460A was not found. The G11778A mutation, older age, and male gender are associated with poor vision outcomes.

Leber hereditary optic neuropathy following head trauma and ocular trauma on contralateral eye: a case report

Purpose

To present a case of activation of Leber hereditary optic neuropathy (LHON) following head and ocular trauma of the fellow eye in the patient with no remarkable symptoms and normal visual acuity prior to trauma.

Case summary

A 31-year-old healthy man was referred to our hospital after a traffic accident. He had blowout fractures of medial and inferior orbital wall of the left eye, subcutaneous hematoma of the left forehead, and bony fragment that compressed the left optic nerve. Initially, best-corrected visual acuity (BCVA) was 20/20 in the right and 20/1000 in the left eyes. Relative afferent pupillary defect of the left eye was apparent, and fundus examination revealed choroidal rupture circumferentially crossing the macular area. Nine months later, the patient complained with gradual vision loss in the right eye, which was the contralateral eye of the ocular trauma. BCVA was 20/200, and perimetry revealed cecocentral scotoma in the right eye. BCVA in both eyes reduced to 20/2000 1 year post-trauma. Visual evoked potentials revealed markedly decreased in amplitudes and elongated latencies for both eyes. Mitochondrial DNA analysis revealed a G11778A mutation; therefore, a diagnosis of activation of LHON followed by trauma was made for the previously unaffected carrier.

Conclusions

This is a case in which activation of LHON occurred in a healthy carrier following head and ocular trauma of the fellow eye. This observation suggests the possibility that LHON activation in healthy carriers may occur in patients who experience head or ocular trauma even in the fellow eye.

Performance of the MLPA technique for detecting common mutations in Leber hereditary optic neuropathy

Leber hereditary optic neuropathy (LHON) causes painless vision loss resulting from mitochondrial DNA (mtDNA) mutation. Over 95% of LHON cases result from one of three mtDNA point mutations (m.3460G>A, m.11778G>A, and m.14484T>C). There is no established cure for LHON; early and accurate diagnosis would enable patients to be given appropriate treatments leading to a reduction of the disease progression. To increase the accessibility to molecular genetic testing for LHON, an accurate and cost-effective technique is required. The purpose of this study was to evaluate the accuracy of multiplex ligation-dependent probe amplification (MLPA) for detecting the three common mutations in 18 LHON blood specimens. Validation of the results using direct DNA sequencing technology proved that the MLPA technique had 100% accuracy, with no false-positive results. This study demonstrates that MLPA could provide a highly accurate, economical, and widely accessible technique for routine molecular genetic testing for mitochondrial disorders.

Mitochondrial genetics and therapeutic overview of Leber's hereditary optic neuropathy

Leber's hereditary optic neuropathy (LHON) is a common inherited mitochondrial disorder that is characterized by the degeneration of the optic nerves, leading to vision loss. The major mutations in the mitochondrial genes ND1, ND4, and ND6 of LHON subjects are found to increase the oxidative stress experienced by the optic nerve cell, thereby leading to nerve cell damage. Accurate treatments are not available and drugs that are commercially available like Idebenone, EPI-743, and Bendavia with their antioxidant role help in reducing the oxidative stress experienced by the cell thereby preventing the progression of the disease. Genetic counseling plays an effective role in making the family members aware of the inheritance pattern of the disease. Gene therapy is an alternative for curing the disease but is still under study. This review focuses on the role of mitochondrial genes in causing LHON and therapeutics available for treating the disease. A systematic search has been adopted in various databases using the keywords "LHON," "mitochondria," "ND1," "ND4," "ND6," and "therapy" and the following review on mitochondrial genetics and therapeutics of LHON has been developed with obtained articles from 1988 to 2017.

Leber Hereditary Optic Neuropathy: A Mitochondrial Disease Unique in Many Ways

Leber hereditary optic neuropathy (LHON) was the first mitochondrial disease to be identified as being caused by mutations in the mitochondrial DNA (mtDNA). This disease has been studied extensively in the past two decades, particularly in Brazilian, Chinese and European populations; and many primary mutations have been reported. However, the disease is enigmatic with many unique features, and there still are several important questions to be resolved. The incomplete penetrance, the male-biased disease expression and the prevalence in young adults all defy a proper explanation. It has been reported that the development of LHON is affected by the interaction between mtDNA mutations, mtDNA haplogroup background, nuclear genes, environmental factors and epigenetics. Furthermore, with the help of new animal models for LHON that have been created in recent years, we are continuing to learn more about the mechanism of this disease. The stage has now been reached at which there is a good understanding of both the genetic basis of the disease and its epidemiology, but just how the blindness that follows from the death of cells in the optic nerve can be prevented remains to be a pharmacological challenge. In this chapter, we summarize the progress that has been made in various recent studies on LHON, focusing on the molecular pathogenic mechanisms, clinical features, biochemical effects, the pharmacology and its treatment.

Leber's hereditary optic neuropathy is multiorgan not mono-organ

Leber's hereditary optic neuropathy (LHON) is a maternally inherited mitochondrial disorder with bilateral loss of central vision primarily due to mitochondrial DNA (mtDNA) mutations in subunits of complex I in the respiratory chain (primary LHON mutations), while other mtDNA mutations can also be causative. Since the first description, it is known that LHON is not restricted to the eyes but is a multisystem disorder additionally involving the central nervous system, ears, endocrinological organs, heart, bone marrow, arteries, kidneys, or the peripheral nervous system. Multisystem involvement may start before or after the onset of visual impairment. Involvement of organs other than the eyes may be subclinical depending on age, ethnicity, and possibly the heteroplasmy rate of the responsible primary LHON mutation. Primary LHON mutations may rarely manifest without ocular compromise but with arterial hypertension, various neurodegenerative diseases, or Leigh syndrome. Patients with LHON need to be closely followed up to detect at which point organs other than the eyes become affected. Multiorgan disease in LHON often responds more favorably to symptomatic treatment than the ocular compromise.

Profiling the mitochondrial proteome of Leber's Hereditary Optic Neuropathy (LHON) in Thailand: down-regulation of bioenergetics and mitochondrial protein quality control pathways in fibroblasts with the 11778G>A mutation

Leber's Hereditary Optic Neuropathy (LHON) is one of the commonest mitochondrial diseases. It causes total blindness, and predominantly affects young males. For the disease to develop, it is necessary for an individual to carry one of the primary mtDNA mutations 11778G>A, 14484T>C or 3460G>A. However these mutations are not sufficient to cause disease, and they do not explain the characteristic features of LHON such as the higher prevalence in males, incomplete penetrance, and relatively later age of onset. In order to explore the roles of nuclear encoded mitochondrial proteins in development of LHON, we applied a proteomic approach to samples from affected and unaffected individuals from 3 pedigrees and from 5 unrelated controls. Two-dimensional electrophoresis followed by MS/MS analysis in the mitochondrial lysate identified 17 proteins which were differentially expressed between LHON cases and unrelated controls, and 24 proteins which were differentially expressed between unaffected relatives and unrelated controls. The proteomic data were successfully validated by western blot analysis of 3 selected proteins. All of the proteins identified in the study were mitochondrial proteins and most of them were down regulated in 11778G>A mutant fibroblasts. These proteins included: subunits of OXPHOS enzyme complexes, proteins involved in intermediary metabolic processes, nucleoid related proteins, chaperones, cristae remodelling proteins and an anti-oxidant enzyme. The protein profiles of both the affected and unaffected 11778G>A carriers shared many features which differed from those of unrelated control group, revealing similar proteomic responses to 11778G>A mutation in both affected and unaffected individuals. Differentially expressed proteins revealed two broad groups: a cluster of bioenergetic pathway proteins and a cluster involved in protein quality control system. Defects in these systems are likely to impede the function of retinal ganglion cells, and may lead to the development of LHON in synergy with the primary mtDNA mutation.

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.

Fifteen novel mutations in the mitochondrial NADH dehydrogenase subunit 1, 2, 3, 4, 4L, 5 and 6 genes from Iranian patients with Leber's hereditary optic neuropathy (LHON)

Leber's hereditary optic neuropathy (LHON) is an optic nerve dysfunction resulting from mutations in mitochondrial DNA (mtDNA), which is transmitted in a maternal pattern of inheritance. It is caused by three primary point mutations: G11778A, G3460A and T14484C; in the mitochondrial genome. These mutations are sufficient to induce the disease, accounting for the majority of LHON cases, and affect genes that encode for the different subunits of mitochondrial complexes I and III of the mitochondrial respiratory chain. Other mutations are secondary mutations associated with the primary mutations. The purpose of this study was to determine MT-ND variations in Iranian patients with LHON. In order to determine the prevalence and distribution of mitochondrial mutations in the LHON patients, their DNA was studied using PCR and DNA sequencing analysis. Sequencing of MT-ND genes from 35 LHON patients revealed a total of 44 nucleotide variations, in which fifteen novel variations-A14020G, A13663G, C10399T, C4932A, C3893G, C10557A, C12012A, C13934T, G4596A, T12851A, T4539A, T4941A, T13255A, T14353C and del A 4513-were observed in 27 LHON patients. However, eight patients showed no variation in the ND genes. These mutations contribute to the current database of mtDNA polymorphisms in LHON patients and may facilitate the definition of disease-related mutations in human mtDNA. This research may help to understand the disease mechanism and open up new diagnostic opportunities for LHON.

Complete mitochondrial DNA sequence analysis in two southern Chinese pedigrees with Leber hereditary optic neuropathy revealed secondary mutations along with the primary mutation

AIM

To investigate mitochondrial factors associated with Leber hereditary optic neuropathy (LHON) through complete sequencing and analysis of the mitochondrial genome of Chinese patients with this disease.

METHODS

Two unrelated southern Chinese families with LHON and 10 matched healthy controls were recruited, and their entire mitochondrial DNA (mtDNA) was amplified and sequenced with the universal M13 primer. Then DNA sequence analysis and variation identification were perfomed by DNAssist and Chromas 2 software and compared with authoritative databases such as Mitomap.

RESULTS

Mutational analysis of mtDNA in these two Chinese pedigrees revealed one common LHON-associated mutation, G11778A (Arg→His), in the MT-ND4 gene. In addition, there were two secondary mutations in Pedigree 1: C3497T (Ala→Val), and C3571T (Leu→Phe) in the MT-ND1 gene, which have not been reported; and two secondary mutations occurred in Pedigree 2: A10398G (Thr→Ala) in the MT-ND3 gene, and T14502C (Ile→Val) in the MT-ND6 gene. Three polymorphisms, A73G, G94A and A263G in the mtDNA control region, were also found.

CONCLUSION

Our study confirmed that the known MT-ND4*G11778A mutation is the most significant cause of LHON. The C3497T and C3571T mutations in Pedigree 1 were also both at hot-spots of MT-ND1; they may affect the respiratory chain in coordination with the primary mutation G11778A. In Pedigree 2, the two secondary mutations A10398G of MT-ND3 and T14502C of MT-ND6 may influence mitochondrial respiratory complex I, leading to the mitochondrial respiratory chain dysfunction which results in optic atrophy together with G11778A. Therefore, not only the common primary LHON mutation is responsible for the visual atrophy, but other secondary mtDNA mutations should also be considered when giving genetic counseling.

Large-scale screening of mitochondrial DNA mutations among Iranian patients with prelingual nonsyndromic hearing impairment

Hereditary hearing impairment (HI) is a genetically heterogeneous disorder caused by mutations either in nuclear DNA (nDNA) or in mitochondrial DNA (mtDNA). The nDNA mutations account for the majority of prelingual nonsyndromic HI (NSHI). The present survey was conducted to screen for known pathogenic mtDNA mutations including A1555G, A3243G, C1494T, and A7445G to provide an accurate estimate of their prevalence in prelingual NSHI for the first time in the Iranian subpopulations. One thousand unrelated probands with NSHI (including both GJB2-negative and GJB2 heterozygote cases) and 1000 healthy matched controls were investigated using the PCR/RFLP method followed by DNA sequencing to confirm the observed mtDNA mutations. Two of the studied mutations, namely A3243G and A7445G, were each found in a single family (a frequency of 0.1% for each). Mutation screening for A3243G followed by DNA sequencing led to the identification of G3316A substitution, with no prior link to HI. Surprisingly, screening for A3243G in the studied population identified 6 cases (0.6%) in probands and 10 (1%) in normal subjects. A1555G, the most common mtDNA mutation associated with deafness in other populations, was not found in the studied samples. To conclude, our findings indicate G3316A as a nonpathogenic variant in the prelingual NSHI subpopulations of Iran and suggest that mtDNA mutations do not play a major role in the etiology of NSHI in Iran.

Detection of somatic mutations and germline polymorphisms in mitochondrial DNA of uterine fibroids patients

To identify the role of mitochondrial DNA (mtDNA) mutations in uterine fibroids patients, genomic DNA isolated from paired myometrium and fibroid tissues was screened for mutations. The present study represents the first investigation to report that 10.4% of uterine fibroids cases had either mtDNA mutations or polymorphisms or both. Among the 14 mitochondrial sequence variants identified, seven are somatic mutations (A3327C, G3352A, G3376A, G3380A, G3421A, T15312G, and C15493G) and the remaining (G3316A, C3342A, C3442T, T10205A, A10188G, A10229C, and A10301T) are gene polymorphisms. Somatic mutations were both homo- and heteroplasmic in nature. Of the seven somatic mutations located in the MTND1 and MTCYB genes, five (71.42%) are nonsynonymous in nature, whereas four (57.14%) of the polymorphisms located in MTND1 and MTND3 genes are found to be nonsynonymous. Sequence variants such as G3380A, G3421A, T15312G, G3376A, and G3316A have been earlier described in different human pathologies, but the remaining are novel ones. Mitochondrial somatic mutations and polymorphisms may predispose women to an earlier onset of degenerative cellular processes, which impair oxidative phosphorylation capacity and thereby promote tumorigenesis in uterine smooth muscle cells. Detection of mtDNA sequence variations in fibroid patients raises the need for larger case-control studies to screen the whole mitochondrial genome and evaluate as a future diagnostic biomarker in fibroid patients.

Leber's Hereditary Optic Neuropathy-Gene Therapy: From Benchtop to Bedside

Leber's hereditary optic neuropathy (LHON) is a maternally transmitted disorder caused by point mutations in mitochondrial DNA (mtDNA). Most cases are due to mutations in genes encoding subunits of the NADH-ubiquinone oxidoreductase that is Complex I of the electron transport chain (ETC). These mutations are located at nucleotide positions 3460, 11778, or 14484 in the mitochondrial genome. The disease is characterized by apoplectic, bilateral, and severe visual loss. While the mutated mtDNA impairs generation of ATP by all mitochondria, there is only a selective loss of retinal ganglion cells and degeneration of optic nerve axons. Thus, blindness is typically permanent. Half of the men and 10% of females who harbor the pathogenic mtDNA mutation actually develop the phenotype. This incomplete penetrance and gender bias is not fully understood. Additional mitochondrial and/or nuclear genetic factors may modulate the phenotypic expression of LHON. In a population-based study, the mtDNA background of haplogroup J was associated with an inverse relationship of low-ATP generation and increased production of reactive oxygen species (ROS). Effective therapy for LHON has been elusive. In this paper, we describe the findings of pertinent published studies and discuss the controversies of potential strategies to ameliorate the disease.

Genome-wide linkage scan and association study of PARL to the expression of LHON families in Thailand

Leber hereditary optic neuropathy (LHON) is the most common mitochondrially inherited disease causing blindness, preferentially in young adult males. Most of the patients carry the G11778A mitochondrial DNA (mtDNA) mutation. However, the marked incomplete penetrance and the gender bias indicate some additional genetic and/or environmental factors to disease expression. Herein, we first conducted a genome-wide linkage scan with 400 microsatellite markers in 9 large Thai LHON G11778A pedigrees. Using an affecteds-only nonparametric linkage analysis, 4 regions on chromosomes 3, 12, 13 and 18 showed Zlr scores greater than 2 (P < 0.025), which is consistently significant across several linkage statistics. The most suggestive marker D3S1565 (Zlr > 2 in 10 of 16 allele sharing models tested) was then expanded to include the region 3q26.2-3q28 covering SLC7A14 (3q26.2), MFN1 (3q26.32), MRPL47 (3q26.33), MCCC1 (3q27.1), PARL (3q27.1) and OPA1 (3q28-q29). All of these candidate genes were selected from the Maestro database and had known to be localized in mitochondria. Sixty tag SNPs were genotyped in 86 cases, 211 of their relatives and 32 unrelated Thai controls, by multiplex-PCR-based Invader assay. Analyses using a powerful association testing tool that adjusts for relatedness (the M(QLS) statistic) showed the most evidence of association between two SNPs, rs3749446 and rs1402000 (located in PARL presenilins-associated rhomboid-like) and LHON expression (both P = 8.8 x 10(-5)). The mitochondrial PARL protease has been recently known to play a role with a dynamin-related OPA1 protein in preventing apoptotic events by slowing down the release of cytochrome c out of mitochondrial cristae junctions. Moreover, PARL is required to activate the intramembranous proteolyses resulting in the degradation of an accumulated pro-apoptotic protein in the outer mitochondrial membrane. Under these circumstances, variants of PARL are suggested to influence cell death by apoptosis which has long been believed to intrigue the neurodegeneration of LHON.

Mitochondrial DNA and its mutations: novel fields in a new era

Az utóbbi két évtizedet tartják a klinikai mitokondriális DNS-kutatás aranykorának. Folyamatosan bővül a patológiás variánsok száma, amelyek betegséggel társulnak, illetve bővül az ismeretanyag azokról az entitásokról, melyek hátterében a mitokondriális DNS kóros elváltozásai állnak. A cirkuláris mitokondriális DNS öröklődése eltér a Mendel-féle szabályoktól, anyai öröklésmenetet mutat; számos vonatkozásban eltérő sajátosságokkal rendelkezik a nukleáris DNS-hez viszonyítva. A molekuláris biológiai módszerek terjedésével egyre több kórkép ismerhető fel, noha a diagnosztika manapság is komoly kihívást jelent. Napjainkban a mitokondriális medicina számos orvosi szubspecialitáshoz kapcsolódóan jelentős előrelépéseket mutatott; így körvonalazódott a mitokondriális gasztroenterológia, endokrinológia, otológia, oftalmológia, nefrológia, hematológia, onkológia, reproduktív medicina és pszichiátria, mintegy az adott szubspecialitás mitokondriális DNS-sel kapcsolatos, többé-kevésbé részleges önállósodással megjelenő territóriuma. A jelen összefoglaló közlemény a mitokondriális medicina rövid, általános összefoglalása mellett e fejezetekre próbál rátekintést nyújtani.

Transmission of heteroplasmic G11778A in extensive pedigrees of Thai Leber hereditary optic neuropathy

Leber hereditary optic neuropathy (LHON) is characterized by the acute or subacute bilateral painless loss of central vision, predominantly in young males. G11778A is the most common mitochondrial DNA mutation responsible for the disease. Thirty-seven percent of our LHON pedigrees (which is a much higher prevalence than that generally found) carried heteroplasmic G11778A. Analyses of four large Thai LHON pedigrees spanning four to six generations strongly suggested that the transmission of the heteroplasmic G11778A mutation is under selective pressure in favour of the mutated allele and that heteroplasmy influences the disease expression.

Molecular epidemiology of mtDNA mutations in 903 Chinese families suspected with Leber hereditary optic neuropathy

We report the molecular epidemiology of three primary mutations in mitochondrial DNA (mtDNA) responsible for Leber hereditary optic neuropathy (LHON) based on analysis of probands suspected with LHON from 903 Chinese families. Most of them had optic neuropathy of unknown cause, and only 128 had a family history of optic neuropathy. Mutations in the mtDNA were detected in 346 probands. Of the 346 cases, 340 were homoplasmic and only six were heteroplasmic; 284 were male and 62 were female; 120 had a family history and 226 were sporadic. G11778A, T14484C and G3460A mutations were detected in 312 (90.2%), 30, and four families, respectively. The majority (226/346, 65.3%) of all LHON cases in Chinese are sporadic. These 226 probands (29.2%) were identified from 775 probands with sporadic optic neuropathy. Affected male-to-female ratio was 4.6:1 for all probands but was 2.2:1 for family members. Average age at onset was 18.5 years, ranging from 4.5 to 47 years old.