A novel start codon mutation of the MERTK gene in a patient with retinitis pigmentosa.

PURPOSE: Retinitis pigmentosa (RP) is a clinically and genetically heterogeneous group of inherited retinal degenerations characterized by progressive loss of photoreceptor cells and RPE functions. More than 70 causative genes are known to be responsible for RP. This study aimed to identify the causative gene in a patient from a consanguineous family with childhood-onset severe retinal dystrophy. METHODS: To identify the defective gene, whole exome sequencing was performed. Candidate causative variants were selected and validated using Sanger sequencing. Segregation analysis of the causative gene was performed in additional family members. To verify that the mutation has an effect on protein synthesis, an expression vector containing the first ten amino acids of the mutant protein fused with the DsRed2 fluorescent protein was constructed and transfected into HEK293T cells. Expression of the fusion protein in the transfected cells was measured using fluorescence microscopy. RESULTS: By filtering against public variant databases, a novel homozygous missense mutation (c.3G>A) localized in the start codon of the MERTK gene was detected as a potentially pathogenic mutation for autosomal recessive RP. The c.3G>A mutation cosegregated with the disease phenotype in the family. No expression of the first ten amino acids of the MerTK mutant fused with the DsRed2 fluorescent protein was detected in HEK293T cells, indicating that the mutation affects the translation initiation site of the gene that may lead to loss of function of the MerTK signaling pathway. CONCLUSIONS: We report a novel missense mutation (c.3G>A, p.0?) in the MERTK gene that causes severe vision impairment in a patient. Taken together with previous reports, our results expand the spectrum of MERTK mutations and extend our understanding of the role of the MerTK protein in the pathogenesis of retinitis pigmentosa.

Mitochondrial DNA history of Sri Lankan ethnic people: their relations within the island and with the Indian subcontinental populations.

Located only a short distance off the southernmost shore of the Greater Indian subcontinent, the island of Sri Lanka has long been inhabited by various ethnic populations. Mainly comprising the Vedda, Sinhalese (Up- and Low-country) and Tamil (Sri Lankan and Indian); their history of settlements on the island and the biological relationships among them have remained obscure. It has been hypothesized that the Vedda was probably the earliest inhabitants of the area, followed by Sinhalese and Tamil from the Indian mainland. This study, in which 271 individuals, representing the Sri Lankan ethnic populations mentioned, were typed for their mitochondrial DNA (mtDNA) hypervariable segment 1 (HVS-1) and part of hypervariable segment 2 (HVS-2), provides implications for their settlement history on the island. From the phylogenetic, principal coordinate and analysis of molecular variance results, the Vedda occupied a position separated from all other ethnic people of the island, who formed relatively close affiliations among themselves, suggesting a separate origin of the former. The haplotypes and analysis of molecular variance revealed that Vedda people's mitochondrial sequences are more related to the Sinhalese and Sri Lankan Tamils' than the Indian Tamils' sequences. MtDNA haplogroup analysis revealed that several West Eurasian haplogroups as well as Indian-specific mtDNA clades were found amongst the Sri Lankan populations. Through a comparison with the mtDNA HVS-1 and part of HVS-2 of Indian database, both Tamils and Sinhalese clusters were affiliated with Indian subcontinent populations than Vedda people who are believed to be the native population of the island of Sri Lanka.

Identification of the variants in PARL, the nuclear modifier gene, responsible for the expression of LHON patients in Thailand.

The present study explored variation in the PARL gene as one of the potential nuclear modifiers in the pathogenesis of Leber hereditary optic neuropathy (LHON). Ten exons, their franking introns and 3' UTR of the PARL gene were analysed. Seventeen SNPs detected were investigated in 83 affected and 53 unaffected individuals from 47 independent Thai LHON pedigrees using MQLS statistics in order to minimize the influence of the family background. Three intronic SNPs (rs953419, rs3749446 and rs1402000) showed statistically significant results. Joint haplotypes were constructed based on the genotypes at 3 SNPs and 7 possible haplotypes were observed in the 136 subjects. Our findings that the frequency of the haplotype AAC, and AAT were significantly higher in the unaffected cases and the frequencies of haplotype GGT were significantly higher in LHON cases, indicate that it might have a role in the penetrance of this mitochondrial disease.

Clinical expression and mitochondrial deoxyribonucleic acid study in twins with 14484 Leber's hereditary optic neuropathy: A case report.

BACKGROUND: This study aimed to explore clinical and molecular factors that cause discordance for clinical expression of Leber's hereditary optic neuropathy (LHON) in a pair of identical twins with the 14484 point mutation. CASE SUMMARY: Twin patients with the 14484 point mutation were studied for zygosity by using the Short Tandem Repeats Typing system. For the monozygotic twins, the radioactive restriction and densitometric analyses were used to quantitate the heteroplasmy level for the 14484 point mutation. The mitochondrial genome was analyzed to determine influential factors by mitochondrial deoxyribonucleic acid (DNA) sequencing, denaturing high-performance liquid chromatography and next generation sequencing. For the dizygotic twins, the nuclear DNA was analyzed. The twins with 14484 LHON were monozygotic with homoplasmy. No difference in the point mutation in mitochondrial DNA was found. No modifying genes that potentially influenced the disparity in phenotypic expression of LHON were detected in these twins. CONCLUSION: This 11-year follow-up of monozygotic twins showed additional genetic modifications and epigenetic factors are possibly associated with discordance for LHON.

Association of Mitochondrial DNA Polymorphisms With Pediatric-Onset Cyclic Vomiting Syndrome.

Background: Cyclic vomiting syndrome (CVS) is a functional gastrointestinal disorder characterized by recurrent stereotypic episodes of vomiting. The pathophysiology of CVS remains obscure. Previous studies have supported the hypotheses of mitochondrial dysfunction. However, data on association studies between mitochondrial DNA (mtDNA) polymorphisms and pediatric-onset CVS are limited and inconsistent. The aims of this study were to describe clinical characteristics, evaluate association of mtDNA polymorphisms 16519T and 3010A with pediatric-onset CVS and identify new mtDNA candidate variants. Methods: This study involved Thai patients diagnosed with CVS according to the Rome III or IV criteria before the age of 15 years. Patients' demographic data, clinical characteristics, previous investigations and treatment outcomes were obtained. Blood samples were collected for next-generation (whole exome) sequencing, followed by analysis of chromosome M (mitochondrial. Variants were filtered according to clinical significance using ClinVar and MITOMAP. mtDNA polymorphisms in 148 normal Thai individuals were used as controls. Results: Forty-eight children were enrolled in the clinical study, and 30 participated in the genetic analysis. The median age at onset and median age at diagnosis was 3.0 (1.5-5.6) and 6.3 (3.0-8.6) years, respectively. Maternal history of migraine was positive in 16.7%. About 45.7% (21 of 46) of the patients achieved complete clinical remission, with the mean symptom duration of 5.9 ± 3.3 years. The prevalence of mtDNA variants 16519T and 3010A among the patient group and Thai general population (control) were as follows: 40.0% (12/30) vs. 27.7% (P = 0.18) and 6.7% (2/30) vs. 0.7% (P = 0.07), respectively. Five known pathogenic variants were identified in 6 patients, including mtDNA 8528C in one patient who also had infantile hypertrophic cardiomyopathy. Six likely pathogenic variants were found but without statistical significance. We identified 11 variants with significant prevalence in the patient group. Though, these variants were classified as variants of unknown significance (VUS), several of them were located in mt functional regions and therefore they deserve further investigations as new candidates for association with pediatric CVS. Conclusion: There were no associations of mtDNA polymorphisms 16519T and 3010A with CVS in our pediatric cohort. Five pathogenic variants and 11 VUS were found associated with pediatric-onset CVS.

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.

Genetic history of Southeast Asian populations as revealed by ancient and modern human mitochondrial DNA analysis.

The 360 base-pair fragment in HVS-1 of the mitochondrial genome were determined from ancient human remains excavated at Noen U-loke and Ban Lum-Khao, two Bronze and Iron Age archaeological sites in Northeastern Thailand, radio-carbon dated to circa 3,500-1,500 years BP and 3,200-2,400 years BP, respectively. These two neighboring populations were parts of early agricultural communities prevailing in northeastern Thailand from the fourth millennium BP onwards. The nucleotide sequences of these ancient samples were compared with the sequences of modern samples from various ethnic populations of East and Southeast Asia, encompassing four major linguistic affiliations (Altaic, Sino-Tibetan, Tai-Kadai, and Austroasiatic), to investigate the genetic relationships and history among them. The two ancient samples were most closely related to each other, and next most closely related to the Chao-Bon, an Austroasiatic-speaking group living near the archaeological sites, suggesting that the genetic continuum may have persisted since prehistoric times in situ among the native, perhaps Austroasiatic-speaking population. Tai-Kadai groups formed close affinities among themselves, with a tendency to be more closely related to other Southeast Asian populations than to populations from further north. The Tai-Kadai groups were relatively distant from all groups that have presumably been in Southeast Asia for longer-that is, the two ancient groups and the Austroasiatic-speaking groups, with the exception of the Khmer group. This finding is compatible with the known history of the Thais: their late arrival in Southeast Asia from southern China after the 10th-11th century AD, followed by a period of subjugation under the Khmers.

Characterization of 2-deoxy-D-glucose uptake in fibroblast cultures derived from patients with A3243G mitochondrial DNA mutation.

We investigated cellular glucose uptake of fibroblast cultures derived from seven patients with mitochondrial DNA (mtDNA) A3243G mutation and from six healthy controls with no mtDNA mutations. Heteroplasmy of fibroblast cultures were shifted by culturing for 5 days in galactose-containing medium. The proportion of mutant mtDNA decreased by 7.7% to 10% in three patient fibroblast cultures, whereas 2-deoxy-D-glucose uptake increased 1.8-2.1-fold at basal state, 1.9-2.3-fold in the presence of 60 ng/ml of insulin, and 1.8-2.1-fold in 100 ng/ml of insulin. No significant changes in level of heteroplasmy or glucose uptake were observed in the other patients samples and control samples. This study showed that alteration in the proportion of fibroblast mtDNA A3243G mutation content directly affected basal and insulin-stimulated glucose uptake.

The prehistoric peopling of Southeast Asia.

The human occupation history of Southeast Asia (SEA) remains heavily debated. Current evidence suggests that SEA was occupied by Hòabìnhian hunter-gatherers until ~4000 years ago, when farming economies developed and expanded, restricting foraging groups to remote habitats. Some argue that agricultural development was indigenous; others favor the "two-layer" hypothesis that posits a southward expansion of farmers giving rise to present-day Southeast Asian genetic diversity. By sequencing 26 ancient human genomes (25 from SEA, 1 Japanese Jomon), we show that neither interpretation fits the complexity of Southeast Asian history: Both Hòabìnhian hunter-gatherers and East Asian farmers contributed to current Southeast Asian diversity, with further migrations affecting island SEA and Vietnam. Our results help resolve one of the long-standing controversies in Southeast Asian prehistory.

Whole Exome Sequencing in Eight Thai Patients With Leber Congenital Amaurosis Reveals Mutations in the CTNNA1 and CYP4V2 Genes.

Purpose: Our goal was to describe the clinical and molecular genetic findings in Thai patients with Leber congenital amaurosis (LCA). Methods: Whole exome sequencing (WES) was performed in eight unrelated patients. All genes responsible for inherited retinal diseases (IRDs) based on RetNet were selected for analysis. Potentially causative variants were filtered through a bioinformatics pipeline and validated using Sanger sequencing. Segregation analysis of the causative genes was performed in family members when available. Results: Eleven deleterious variants, six nonsense and five missense, were identified in seven genes: four LCA-associated genes (CEP290, IQCB1, NMNAT1, and RPGRIP1), one gene responsible for syndromic LCA (ALMS1), and two IRDs-related genes (CTNNA1 and CYP4V2). Clinical reassessment supported the diagnosis of syndromic LCA in those patients harboring potentially pathogenic variants in the ALMS1. Interestingly, two causative genes, CTNNA1 and CYP4V2, previously reported to cause butterfly-shaped pigment dystrophy (BSPD) and Bietti's crystalline dystrophy (BCD), respectively, were detected in two other patients. These two patients developed rapid and severe visual loss in contrast to BSPD and BCD patients in previous studies. The results of this study demonstrate that causative variants identified in the CTNNA1 and CYP4V2 genes are also associated with LCA. Conclusions: This is the first report describing the molecular genetics and clinical manifestations of Thai patients with LCA. The present study expands the spectrum of LCA-associated genes, which is a benefit for molecular diagnosis. The identification of mutations in the CTNNA1 and CYP4V2 genes requires further elucidation in larger cohorts with LCA.

Case report: A Thai patient with Leber's hereditary optic neuropathy linked to mitochondrial DNA 14484 mutation.

A young Thai male presented with bilateral visual loss and disc pallor. The 14484 mutation responsible for Leber's hereditary optic neuropathy (LHON) was identified on blood mitochondrial analysis. His visual loss was more severe than the visual loss described in Caucasian and Japanese patients and showed no improvement. He had no other identifiable mutations related to LHON nor any associated neurological disorder. This is the first case report of LHON with the 14484 mutation in a Thai patient.

Oculopharyngodistal myopathy in a Thai family.

There has been controversy whether oculopharyngodistal myopathy (OPDM) commonly seen in Japan is a distinct disease entity or a variant of oculopharyngeal muscular dystrophy (OPMD) initially described in French-Canadians and has since been reported in other ethnic groups. Both diseases have autosomal dominant inheritance and OPDM patients are clinically similar to OPMD with slowly progressive ptosis, ophthalmoplegia and dysphagia except that most of the former usually have distal as opposed to proximal weakness and most of them are genetically different from the latter The authors report here 2 siblings with clinical features of OPDM. This entity is rare outside Japan and this is the first family to be reported from Thailand

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.

Development of a SNP set for human identification: A set with high powers of discrimination which yields high genetic information from naturally degraded DNA samples in the Thai population.

This study describes the development of a SNP typing system for human identification in the Thai population, in particular for extremely degraded DNA samples. A highly informative SNP marker set for forensic identification was identified, and a multiplex PCR-based Invader assay was developed. Fifty-one highly informative autosomal SNP markers and three sex determination SNP markers were amplified in two multiplex PCR reactions and then detected using Invader assay reactions. The average PCR product size was 71 base pairs. The match probability of the 54-SNP marker set in 124 Thai individuals was 1.48×10(-21), higher than that of STR typing, suggesting that this 54-SNP marker set is beneficial for forensic identification in the Thai population. The selected SNP marker set was also evaluated in 90 artificially degraded samples, and in 128 naturally degraded DNA samples from real forensic casework which had shown no profiles or incomplete profiles when examined using a commercial STR typing system. A total of 56 degraded samples (44%) achieved the matching probability (PM) equivalent to STR gold standard analysis (successful genotyping of 44 SNP markers) for human identification. These data indicated that our novel 54-SNP marker set provides a very useful and valuable approach for forensic identification in the Thai population, especially in the case of highly to extremely degraded DNA. In summary, we have developed a set of 54 Thai-specific SNPs for human identification which have higher discrimination power than STR genotyping. The PCRs for these 54 SNP markers were successfully combined into two multiplex reactions and detected with an Invader assay. This novel SNP genotyping system also yields high levels of genetic information from naturally degraded samples, even though there are much more difficult to recover than artificially degraded samples.

Whole exome sequencing in Thai patients with retinitis pigmentosa reveals novel mutations in six genes.

PURPOSE: To identify disease-causing mutations and describe genotype-phenotype correlations in Thai patients with nonsyndromic retinitis pigmentosa (RP). METHODS: Whole exome sequencing was performed in 20 unrelated patients. Eighty-six genes associated with RP, Leber congenital amaurosis, and cone-rod dystrophy were analyzed for variant detection. RESULTS: Seventeen variants (13 novel and 4 known) in 13 genes were identified in 11 patients. These variants include 10 missense substitutions, 2 nonsense mutations, 3 deletions, 1 insertion, and 1 splice site change. Nine patients with identified inheritance patterns carried a total of 10 potentially pathogenic mutations located in genes CRB1, C8orf37, EYS, PROM1, RP2, and USH2A. Three of the nine patients also demonstrated additional heterozygous variants in genes ABCA4, GUCY2D, RD3, ROM1, and TULP1. In addition, two patients carried variants of uncertain significance in genes FSCN2 and NR2E3. The RP phenotypes of our patients were consistent with previous reports. CONCLUSIONS: This is the first report of mutations in Thai RP patients. These findings are useful for genotype-phenotype comparisons among different ethnic groups.

Polyglutamined expanded androgen receptor interacts with chaperonin CCT.

CCT chaperonin is a highly conserved molecular chaperone, which plays an important role in the folding of complex proteins in mammalian cells. CCT chaperonin interacts with huntingtin and results in decrease of aggregate formation followed by increase of cell survival. Using yeast-two-hybrid system, we screen for specific CCT chaperonin subunit, which can recognize and bind to androgen receptor. We show that subunit 6 of CCT chaperonin interacts with androgen receptor. Interestingly, CCT chaperonin shows higher binding affinity to polyglutamine expanded androgen receptor than that of the wild-type. We prove this interaction in mammalian cell models, which show co-localization of androgen receptor and subunit 6 of CCT in cellular cytosol. Therefore, not only huntingtin but also androgen receptor is a polyglutamine expanded protein, which is a substrate of CCT chaperonin. Our results suggest that CCT might play an essential role in modulation of folding of polyglutamine expanded proteins and could be another target for further therapeutic studies.

Stability of epitheliotrophic factors in autologous serum eye drops from chronic Stevens-Johnson syndrome dry eye compared to non-autoimmune dry eye.

PURPOSE: To compare the concentrations of epitheliotrophic factors in autologous serum eye drops (ASE) prepared from sera of chronic Stevens-Johnson syndrome (SJS) patients with dry eyes to those prepared from non-autoimmune dry eye controls and to study the stability of the epitheliotrophic factors in different storage conditions. METHODS: Twenty-percent ASE were prepared from 10 chronic SJS patients with dry eyes and 10 age-matched non-autoimmune dry eye controls. The concentrations of major epitheliotrophic factors comprising epidermal growth factor (EGF), transforming growth factor-beta1 (TGF-ß1), transforming growth factor-beta2 (TGF-ß2), and fibronectin in those ASE preparations were determined by enzyme-linked immunosorbent assay (ELISA) at baseline and after different storage conditions: at 4 °C for 1 week and 1 month; and at -20 °C for 1, 3 and 6 months. RESULTS: There were no significant differences in the concentrations of EGF, TGF-ß1, TGF-ß2 and fibronectin in 20% ASE between the SJS and control groups (EGF: 176.9 ± 40.9 vs. 185.5 ± 36.9 pg/mL, TGF-ß1: 9.5 ± 2.1 vs. 9.5 ± 1.9 ng/mL, TGF-ß2: 55.3 ± 30.0 vs. 63.91 ± 45.6 pg/mL and fibronectin: 70.5 ± 20.2 vs. 62.2 ± 21.3 µg/mL, respectively). These factors were stable at 4 °C for up to 1 month. Storage at -20 °C for up to 6 months resulted in a slight decrease in TGF-ß1 (SJS: from 9.5-8.4 ng/mL, p < 0.01 and control: from 9.5-8.1 ng/mL, p < 0.01). CONCLUSIONS: The results suggested that the epitheliotrophic capacity of ASE from chronic SJS should be comparable to those from non-autoimmune dry eye patients, and that ASE should be sufficiently stable for up to 6 months, if stored properly at -20 °C.

Mitochondrial haplogroup background may influence Southeast Asian G11778A Leber hereditary optic neuropathy.

PURPOSE: To investigate the role of mitochondrial DNA (mt DNA) background on the expression of Leber hereditary optic neuropathy (LHON) in Southeast Asian carriers of the G11778A mutation. METHODS: Complete mtDNA sequences were analyzed from 53 unrelated Southeast Asian G11778A LHON pedigrees in Thailand and 105 normal Thai controls, and mtDNA haplogroups were determined. Clinical phenotypes were tested for association with mtDNA haplogroup, with adjustment for potential confounders such as sex and age at onset. RESULTS: mtDNA subhaplogroup B was significantly associated with LHON. Follow-up analysis narrowed the association down to subhaplogroup B5a1 (P = 0.008). Survival analyses with Cox's proportional hazards modeling on 469 samples (91 affected and 378 unaffected), adjusted for sex and heteroplasmy, revealed that haplogroup B5a1 tended to increase the risk of visual loss, but the trend was not statistically significant. Conversely, haplogroup F, the second most common haplogroup in the control population, was the least frequent haplogroup in LHON. This negative association was narrowed down to subhaplogroup F1 (P = 0.00043), suggesting that haplogroup F1 confers a protective effect. The distributions of sex, age at onset and heteroplasmy were not significantly different among haplogroups. CONCLUSIONS: The specific mtDNA background B5a1 was significantly associated with Southeast Asian G11778A LHON and appeared to modify the risk of visual loss.

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.

Mitochondrial DNA haplogroup distribution in pedigrees of Southeast Asian G11778A Leber hereditary optic neuropathy.

To investigate the association of mitochondrial DNA (mtDNA) haplogroups and Leber hereditary optic neuropathy (LHON) in the Southeast Asian population, mtDNA haplogroup determination was performed by high-resolution restriction fragment length polymorphism in 42 patients with LHON who were carrying the G11778A mutation and in control subjects drawn from a Thai urban population unaffected by LHON. The patients with LHON were of Thai, Thai-Chinese, and Indian origin. Three mtDNA haplogroups, M, B*, and B, were found in LHON patients in a frequency similar to that in control subjects. mtDNA haplogroup F was found in none of the patients with LHON but was the second most common haplogroup in control subjects. The G11778A mutation must have arisen in our population independently from the mutation in Caucasians. In contrast to Caucasians, no specific mtDNA haplotype was associated with the patients with LHON in the Southeast Asian population. The mitochondrial polymorphisms that modify the expression of LHON in Southeast Asians could not be identified in this study. The lack of haplogroup F in our patients with LHON may indicate the protective effect of this haplogroup in the expression of this disorder.