Development of reverse dot-blot system for screening of mitochondrial DNA mutations associated with Leber hereditary optic atrophy

We developed a diagnostic test based on the reverse dot-blot principle, in which five mitochondrial point mutations responsible for Leber hereditary optic neuropathy (LHON) were screened simultaneously. A series of wild-type and mutant oligonucleotides representing each mutation were covalently bound to a single nylon membrane strip. The target sites were amplified in a multiplex PCR and the products were hybridized to the membrane. Detection is based on chemiluminescence. To test the developed assay, 47 patients suspected of having LHON were screened. In 11 cases (23%) the diagnosis of LHON could be confirmed (3460, 1; 9804, 1; 11778, 5; 14484, 3; 15257, 1). The results suggest that the clinical identification of the mitochondrial defect is not trivial and the availability of a rapid screening method simplifies the molecular analysis of these cases.

Dominant optic atrophy, Kjer type. Linkage analysis and clinical features in a large British pedigree

OBJECTIVES

To perform DNA linkage studies in an extensive 5-generation British pedigree with dominant optic atrophy and to validate the efficacy of domiciliary screening for affected members.

METHODS

Family members received a domiciliary examination based on corrected visual acuity, color vision, visual field defects, and optic disc appearance; DNA linkage analysis was performed using 7 microsatellite markers on 3q27-qter.

RESULTS

Based on the results of the ophthalmic examination, 15 members could be classified as definitely affected, 1 probably affected, and 25 unaffected. Two-point linkage analysis gave significant maximum lod scores at theta [corrected] = 0.00, with the markers D3S3669, D3S3590, and D3S3642. A haplotype segregating with the disease was identified in affected individuals, including the probably affected subject. Informative meioses defined the disease interval between markers D3S1601 and D3S1265.

CONCLUSIONS

Domiciliary screening was effective in identifying all 16 affected members of a British family with dominant optic atrophy. The typical clinical features were present. The location of the OPA1 gene in this new British family seems to be in the 3q27-28 region and is the same as that reported in Danish, Cuban, and French families, suggesting no genetic heterogeneity in this disorder.

Screening for Leber's hereditary optic neuropathy associated mitochondrial DNA mutations in patients with prominent optic neuritis

Previous case reports demonstrated the presence of Leber's hereditary optic neuropathy (LHON) associated mitochondrial (mt) DNA mutations in patients presenting with prominent optic neuritis (PON). By screening the mtDNA, we have excluded the presence of these mutations in 22 patients with PON, indicating that the frequency of these mutations is less than 4.5% in our selected patient population. Reviewing the clinical data of these patients revealed that severe optic nerve atrophy developed in association with both the benign and the severely disabling form of Multiple Sclerosis (MS). This observation suggests that the prominent feature of ON in MS may be related to local factors or to a selective vulnerability of the optic nerve in some patients. However, it also may be consequence of a deleterious process associated with inflammatory demyelination in the central nervous system (CNS) of another, genetically probably distinct subgroup of severely disabled patients.

Fast capillary electrophoresis-laser induced fluorescence analysis of ligase chain reaction products: human mitochondrial DNA point mutations causing Leber's hereditary optic neuropathy

High speed capillary electrophoresis-laser-induced fluorescence (CE-LIF) has been used to separate and detect point mutations using the ligase chain reaction (LCR). The method utilizes short capillary columns (7.5 cm effective length) and fields of 400 V/cm to analyze DNA-ethidium bromide complexes using an He/Ne laser. The method was first demonstrated with a commercially available kit for LCR based on a lacI gene fragment inserted in a Bluescript II phagemid. LCR-CE-LIF was then applied to detect point mutations in human mitochondrial DNA, resulting in Leber's hereditary optic neuropathy (LHON). Three severe mutations were analyzed in which the original base is substituted by a thymidine base at positions 3460, 11778 and 14459. Appropriate primers were designed with polyT tails for length discrimination of pooled samples. Successful detection of mutated samples was achieved, with appropriate correction for small amounts of nonspecific ligated product. The method is rapid, easy to implement, and automatable.

Carbon monoxide poisoning as an epigenetic factor for Leber's hereditary optic neuropathy

A 45-year-old Korean woman visited our hospital complaining of poor vision after carbon monoxide (CO) poisoning. We have confirmed the presence of a point mutation at position 11778 in the ND4 gene of mitochondrial DNA. This case suggests that CO poisoning may precipitate the clinical expression of Leber's hereditary optic neuropathy (LHON). To our knowledge, this would be the first case report of clinical expression of LHON precipitated by CO poisoning.

Preservation of photic blink reflex in Leber's hereditary optic neuropathy

PURPOSE

To examine whether the early response of photic blink reflex (PBR) is spared in patients with Leber's hereditary optic neuropathy (LHON).

METHODS

Twenty-six patients with bilateral optic neuropathy (visual acuity < or = 0.1) and central scotomata were divided into LHON group with one of three mitochondrial DNA mutations at nucleotide position of 3460, 11778, or 14484 and non-LHON group without them. Latencies of the PBR early response and those of the electrically evoked blink reflex (EBR) response were compared among the 26 patients and 20 healthy volunteers.

RESULTS

In controls, average latency of the PBR response was 50.3 +/- 2.4 msec and was in accordance with previous reports. Ten of eleven patients with LHON had normal PBR responses, whereas 12 of 15 controls without LHON had abnormal responses (P = 0.0005). Latencies of EBR responses were normal in all but one patient with LHON.

CONCLUSIONS

The afferent fibers of the PBR early response, as well as those of the light reaction, are reported to terminate presumably in the pretectum. Together with the reported evidence of the preserved light reaction in patients with LHON, we presume that W retinal ganglion cells may project common afferent fibers of these two neuronal pathways and may be preferentially spared in patients with LHON.

Retinal-specific guanylate cyclase gene mutations in Leber's congenital amaurosis

Leber's congenital amaurosis (LCA, MIM 204,000), the earliest and most severe form of inherited retinopathy, accounts for at least 5% of all inherited retinal dystrophies. This autosomal recessive condition is usually recognized at birth or during the first months of life in an infant with total blindness or greatly impaired vision, normal fundus and extinguished electroretinogram (ERG). Nystagmus (pendular type) and characteristic eye poking are frequently observed in the first months of life (digito-ocular sign of Franceschetti). Hypermetropia and keratoconus frequently develop in the course of the disease. The observation by Waardenburg of normal children born to affected parents supports the genetic heterogeneity of LCA. Until now, however, little was known about the pathophysiology of the disease, but LCA is usually regarded as the consequence of either impaired development of photoreceptors or extremely early degeneration of cells that have developed normally. We have recently mapped a gene for LCA to chromosome 17p13.1 (LCA1) by homozygosity mapping in consanguineous families of North African origin and provided evidence of genetic heterogeneity in our sample, as LCA1 accounted for 8/15 LCA families in our series. Here, we report two missense mutations (F589S) and two frameshift mutations (nt 460 del C, nt 693 del C) of the retinal guanylate cyclase (RETGC, GDB symbol GUC2D) gene in four unrelated LCA1 probands of North African ancestry and ascribe LCA1 to an impaired production of cGMP in the retina, with permanent closure of cGMP-gated cation channels.

Brainstem involvement in Leber's hereditary optic neuropathy: association with the 14,484 mitochondrial DNA mutation

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Hereditary cerebellar ataxia with Leber's hereditary optic neuropathy mitochondrial DNA 11778 mutation

We investigated a family with optic atrophy which occurred in childhood or early adulthood plus late-onset cerebellar ataxia. The magnetic resonance imaging in the proband revealed cerebellar atrophy. The proband and her brother were homoplasmic for the most common mitochondrial DNA (mtDNA) 11778 mutation associated with Leber's hereditary optic neuropathy (LHON). This study showed further evidence that central nervous system lesions can occur in cases of LHON mtDNA mutation.

Leber's hereditary optic neuropathy: heteroplasmy is likely to be significant in the expression of LHON in families with the 3460 ND1 mutation

AIM

To assess the effect of heteroplasmy on the expression of Leber's hereditary optic neuropathy (LHON) in a large family with the 3460 LHON mutation.

METHODS

Mutation detection was performed by restriction enzyme digestion of polymerase chain reaction (PCR) products. Heteroplasmy was estimated by quantitation of wild type:mutant product ratios.

RESULTS

There is a significant association between levels of mutant mtDNA and manifestation of the disease phenotype.

CONCLUSION

As a high proportion of families with the 3460 mutation demonstrate heteroplasmy; this is likely to be a significant factor in disease expression.

Mitochondrial DNA mutations in multiple sclerosis patients with severe optic involvement

Preferential maternal transmission in familial cases and the occasional association of multiple sclerosis (MS) and LHON suggests an involvement of mtDNA mutations in the aetiology of MS.

MATERIAL & METHODS

DNA obtained from 100 MS patients with pathological alterations in visually evoked potentials and 100 controls, was used for PCR amplification of mtDNA segments. Mutations were identified by restriction enzyme analysis and DNA sequencing.

RESULTS

Whereas primary LHON mutations are not detected, MS patients show a higher percentage of secondary LHON mutations, usually in a combinatorial manner, than controls. Two neighbouring base pair substitutions that are alleles in a HpaII-polymorphism in the mt tRNA(Thr) gene are significantly more frequent in MS patients than in controls (p = 0.00018).

CONCLUSION

Primary LHON mutations are not characteristic for MS with optic involvement, but secondary LHON mutations and two substitutions abolishing a HpaII site in the mt tRNA(Thr) gene may contribute to the aetiology of MS with optic involvement.

How rapidly does the human mitochondrial genome evolve?

The results of an empirical nucleotide-sequencing approach indicate that the evolution of the human mitochondrial noncoding D-loop is both more rapid and more complex than is revealed by standard phylogenetic approaches. The nucleotide sequence of the D-loop region of the mitochondrial genome was determined for 45 members of a large matrilineal Leber hereditary optic neuropathy pedigree. Two germ-line mutations have arisen in members of one branch of the family, thereby leading to triplasmic descendants with three mitochondrial genotypes. Segregation toward the homoplasmic state can occur within a single generation in some of these descendants, a result that suggests rapid fixation of mitochondrial mutations as a result of developmental bottlenecking. However, slow segregation was observed in other offspring, and therefore no single or simple pattern of segregation can be generalized from the available data. Evidence for rare mtDNA recombination within the D-loop was obtained for one family member. In addition to these germ-line mutations, a somatic mutation was found in the D-loop of one family member. When this genealogical approach was applied to the nucleotide sequences of mitochondrial coding regions, the results again indicated a very rapid rate of evolution.

Peripapillary fluorescein leakage in 11778 Leber's optic neuropathy

A 17-year-old young man presented with a 2-month sequential visual loss in both eyes. Vision was 20/200 in the right eye and 20/400 in the left eye. Both discs were hyperemic with circumpapillary telangiectasia and nerve fiber swelling. Fluorescein angiography revealed a fuzzy hyperfluorescence due to leakage from dilated capillaries on both discs in the late transit. Molecular mitochondrial DNA study confirmed a homoplasmic 11778 Leber's optic neuropathy.

Sequence of mitochondrial DNA in patients with multiple sclerosis

The excess female transmission of multiple sclerosis (MS) and the observation of an MS-like illness in patients with Leber's hereditary optic neuropathy who carry a mitochondrial DNA mutation may indicate that mitochondrial genes contribute to the genetic susceptibility to MS. We sequenced the protein- and RNA-coding sequences of 9 patients with MS who had a family history of MS consistent with maternal transmission. Four base-pair (bp) changes of particular interest were identified. Those at bp 4216 and 4917 may play a role in the etiology of Leber's hereditary optic neuropathy. Two others, at bp 11447 and 14766, were found in all MS patients sequenced. Restriction enzyme analysis used to screen 175 unrelated MS patients and 233 healthy control subjects showed that each of these changes was present in MS patients at a similar frequency to control subjects. The 4216 and 4917 changes were at a higher frequency in north European control subjects than previously documented. We conclude that variation in mitochondrial DNA is unlikely to contribute to susceptibility to MS. The etiology of the overlap between Leber's hereditary optic neuropathy and MS remains unexplained.

Association of the LHON 13,708 and 15,257 mitochondrial DNA mutations with neurodegenerative diseases distinct from LHON

300 patients suffering from neurodegenerative diseases distinct from Leber hereditary optic neuropathy (LHON) were screened for the presence of mitochondrial DNA mutations. We report on nine patients, eight female and one male, who all harboured mutations at positions 13,708 and 15,257 of the mitochondrial DNA. Both mutations have previously been claimed to be associated with LHON. Based on our results, these mutations occur in a number of different neurodegenerative diseases and therefore cannot be regarded as "LHON" mutations.

Leber's hereditary optic neuropathy: clinical and molecular genetic results obtained in a family with a new point mutation at nucleotide position 14498 in the ND 6 gene

Mitochondrial DNA mutations at nucleotide position (np) 3460 in the ND 1 gene, np 11778 in the ND 4 gene, and np 14484 in the ND 6 gene are commonly considered to be associated with the clinical features of Leber's hereditary optic neuropathy (LHON) and account for the majority of LHON cases. Recently, a further mutation in the mtDNA at np 14459 was detected. Herein we report the clinical and the most relevant molecular genetic findings obtained in a LHON family with a new mitochondrial DNA mutations at np 14498 in the ND 6 gene. Clinical and historical data were collected over four generations on three affected and five yet unaffected relatives of the maternal line in this family. All three patients and four of their relatives underwent molecular genetic examination. Two patients and five relatives were also studied clinically. All patients exhibited typical clinical features of LHON. In all yet unaffected relatives, various degrees of peripapillary microangiopathy were found. Molecular analysis did not reveal any of the common LHON mutations. Sequence analysis of the mtDNA of one patient was performed and showed a thymine-to-cytosine exchange at np 14498 in the ND 6 gene, leading to the replacement of an evolutionary highly conserved tyrosine by a cysteine residue. The mutation was not found among 70 other LHON lineages and 180 controls. The new mutation at np 14498 lies in the vicinity of the LHON-related mutations at np 14484 and of the recently described mutation at np 14459, in a region constituting the most evolutionarily conserved part of this polypeptide. That the new mutation at np 14498 is found within this highly conserved region and was not present in any controls implies that this mutation is responsible for LHON in this family.

[Analysis of mutations and heteroplasmy at mitochondrial DNA 11778 using non-RI single strand conformation polymorphisms in Leber's hereditary optic neuropathy]

Leber's hereditary optic neuropathy(LHON) is a maternally inherited mitochondrial disease of an acute or subacute bilateral loss of central vision. G to A substitutions at nucleotide position 11778 in mitochondrial DNA(mt DNA) have been identified in approximately 40% to 90% of patients. In this study, regions containing mt DNA 11778 mutations were analyzed by polymerase chain reaction(PCR), non-RI single strand conformation polymorphisms(SSCP) and direct sequencing. In 26 visually affected patients, mt DNA 11778 mutations were detected in 9 patients (36.4%). In one pedigree of a LHON patient(L-6), four unaffected family members had heteroplasmy of the 11778 mutation using non-RI SSCP. Ratios of the heteroplasmy between wild type and mutant mt DNAs can be detected in non-RI SSCP and accurately quantified by video densitometric analyzer. Two types of novel polymorphisms, 11696 G to A and 11719 A to G, in the mt DNA region were also found in this non-RI SSCP analysis. Non-RI SSCP is an efficient and accurate method for diagnosis of mt DNA 11778 mutations and quantifying heteroplasmy in patients with LHON and pedigrees.

Catalytic activity of complex I in cell lines that possess replacement mutations in the ND genes in Leber's hereditary optic neuropathy

Short-chain ubiquinone analogues act as electron acceptors and as inhibitors in the lymphoblast mitochondria of ND1/3460 mutants, which indicates structural changes in the ubiquinone-binding domain of Complex I in this mutant. The ND4/11778 mutant and two secondary ND5 mutants studied are associated with reductions of at least 50, 35 and 30% in the catalytic rate constant, respectively. However, the efficiency of oxidative phosphorylation is unaffected in all these ND mutants. The rate of respiration is only slightly limited by Complex I in lymphoblast mitochondria. Consequently, there is a 30-35% reduction in the electron flow through Complex I compared with that through Complex II, and an increased lactate/pyruvate ratio, in the ND1 and ND4 mutants, but these factors were unaffected in the secondary ND5 mutants. Energy metabolism is thus less severely affected in the secondary mutants than in the primary mutants, which supports the division into these two categories. An increased ubiquinone-10 content in the mitochondrial membrane of all the mutants, and enhanced succinate dehydrogenase and citrate synthase activities in the ND4 mutant, are proposed to be compensatory changes. The efficiency of these changes and the level of kinetic limitation of respiration by Complex I in each tissue are proposed to determine the clinical development of the disease.

Evidence against an X-linked visual loss susceptibility locus in Leber hereditary optic neuropathy

Pedigree analysis of British families with Leber hereditary optic neuropathy (LHON) closely fits a model in which a pathogenic mtDNA mutation interacts with an X-linked visual loss susceptibility locus (VLSL). This model predicts that 60% of affected females will show marked skewing of X inactivation. Linkage analysis in British and Italian families with genetically proven LHON has excluded the presence of such a VLSL over 169 cM of the X chromosome both when all families were analyzed together and when only families with the bp 11778 mutation were studied. Further, there was no excess skewing of X inactivation in affected females. There was no evidence for close linkage to three markers in the pseudoautosomal region of the sex chromosomes. The mechanism of incomplete penetrance and male predominance in LHON remains unclear.

Stargardt's type maculopathy in a patient with 11778 Leber's optic neuropathy

A 13-year-old boy presented with a 2-month history of blurred vision. Visual acuity was 20/200 in both eyes. Ophthalmoscopic examination revealed normal discs and "beaten bronze atrophy" in the maculae. Subsequently, progressive vision loss with optic atrophy occurred over the next few years. Fluorescein angiographic findings were compatible with Stargardt's maculopathy. Because his cousin developed sequential vision loss diagnosed as Leber's hereditary optic neuropathy, molecular genetic analysis was performed on blood mitochondrial DNA (mtDNA) from our patient, his cousin with vision loss, and another three asymptomatic cousins. The results showed that they all harbored homoplasmic G to A point mutations at nucleotide position 11778 of the ND4 gene in mtDNA.

Evidence of genetic heterogeneity of Leber's congenital amaurosis (LCA) and mapping of LCA1 to chromosome 17p13

Leber's congenital amaurosis (LCA) is an autosomal recessive disease responsible for congenital blindness. It is the earliest and most severe inherited retinal dystrophy in human and its genetic heterogeneity has long been recognised. We have recently reported on the first localisation of a disease gene (LCA1) to the short arm of chromosome 17 by homozygosity mapping in five families of North African origin. Here, we refine the genetic mapping of LCA1 to chromosome 17p13 between loci D17S938 and D17S1353 and provide strong support for the genetic heterogeneity of this condition (maximum likelihood for heterogeneity, 17.20 in InL; heterogeneity versus homogeneity, P = 0.0002, heterogeneity versus no linkage, P < 0.0001)

Respiration and growth defects in transmitochondrial cell lines carrying the 11778 mutation associated with Leber's hereditary optic neuropathy

Mitochondrial DNA from two genetically unrelated patients carrying the mutation at position 11778 that causes Leber's hereditary optic neuropathy has been transferred with mitochondria into human mtDNA-less rho0206 cells. As analyzed in several transmitochondrial cell lines thus obtained, the mutation, which is in the gene encoding subunit ND4 of the respiratory chain NADH dehydrogenase (ND), did not affect the synthesis, size, or stability of ND4, nor its incorporation into the enzyme complex. However, NADH dehydrogenase-dependent respiration, as measured in digitonin-permeabilized cells, was specifically decreased by approximately 40% in cells carrying the mutation. This decrease, which was significant at the 99.99% confidence level, was correlated with a significantly reduced ability of the mutant cells to grow in a medium containing galactose instead of glucose, indicating a clear impairment in their oxidative phosphorylation capacity. On the contrary, no decrease in rotenone-sensitive NADH dehydrogenase activity, using a water-soluble ubiquinone analogue as electron acceptor, was detected in disrupted mitochondrial membranes. This is the first cellular model exhibiting in a foreign nuclear background mitochondrial DNA-linked biochemical defects underlying the optic neuropathy phenotype.