alpha-Tocopherol/lipid ratio in blood is decreased in patients with Leber's hereditary optic neuropathy and asymptomatic carriers of the 11778 mtDNA mutation

OBJECTIVES

Leber's hereditary optic neuropathy (LHON) is a maternally inherited disease characterised by acute or subacute bilateral visual loss in young patients. The primary aetiological event is a mutation in the mitochondrial genome (mtDNA) affecting in most cases mtDNA-encoded subunits of the respiratory chain NADH: coenzyme Q oxidoreductase (complex I). The impaired function of complex I leads to a decline in mitochondrial energy production and enhances free radical generation.

METHODS

The concentrations of some non-enzymatic antioxidants (alpha-tocopherol, beta-carotene, lycopene, glutathione, free sulphydryl groups) and the lipid peroxides in the blood of patients with LHON, carriers with homoplasmic DNA mutation at 11 778, and controls were investigated using high performance liquid chromatography and spectrophotometric methods to assess the function of their antioxidant defence systems.

RESULTS

The alpha-tocopherol/cholesterol+ triglyceride ratio was significantly reduced (p<0.05) both in the patients and asymptomatic carriers. The concentrations of the other antioxidants and the lipid peroxides were not different from those of control subjects.

CONCLUSION

The low concentration of plasma alpha-tocopherol most probably reflects the consumption of the antioxidant by the affected tissues. Furthermore, it suggests that alpha-tocopherol may be the primary scavenger molecule against the free radicals induced by complex I deficiency.

Mutations in the CRB1 gene cause Leber congenital amaurosis

OBJECTIVES

To test the hypothesis that mutations in the CRB1 gene cause Leber congenital amaurosis (LCA) and, if so, to describe the ocular phenotype of patients with LCA who harbor CRB1 sequence variations.

PATIENTS

One hundred ninety probands with a clinical diagnosis of LCA were selected from a cohort of 233 probands ascertained in 5 different countries. The remaining 43 probands (18%) were excluded because they harbored sequence variations in previously identified LCA genes.

METHODS

One hundred ninety unrelated individuals with LCA were screened for coding sequence mutations in the CRB1 gene with single-strand conformation polymorphism analysis followed by automated DNA sequencing.

RESULTS

Twenty-one of the 190 probands (9% of the total cohort of 233) and 2 (1.4%) of 140 controls harbored amino acid-altering sequence variations in the CRB1 gene (P =.003).

CONCLUSIONS

In our cohort of patients with LCA, coding sequence variations were observed in the CRB1 gene more frequently than in any of the other 5 known LCA-associated genes. Likely disease-causing sequence variations have now been identified in 64 (28%) of 233 subjects in this cohort.

CLINICAL RELEVANCE

Molecular diagnosis can confirm and clarify the diagnosis in an increasing fraction of patients with LCA. As genotype data accumulate, clinical phenotypes associated with specific mutations may be established. This will facilitate the counseling of patients regarding their visual prognosis and the likelihood of associated systemic anomalies.

Sequence variations in the NDUFA1 gene encoding a subunit of complex I of the respiratory chain

NDUFA1 is one of the 36 nuclear genes encoding subunits of the mitochondrial complex I involved in the respiratory chain. The human NDUFA1 has been cloned, completely sequenced and mapped to Xq24. In the present study, we searched for sequence variations in NDUFA1 as causative defects in complex I deficiency using genomic DNA of 152 patients with various clinical phenotypes. The patient sample consisted of 54 patients (46 male and 8 female) with Leber heriditary optic neuropathy (LHON) from 48 unrelated families from Germany and 98 patients (72 male and 26 female) with biochemically proven complex I deficiency including Leigh syndrome. Patient DNA was used to amplify all three exons, including the exon/intron boundaries and the promoter region of NDUFA1 for heteroduplex analysis and direct sequencing. In the 152 patients tested, no mutation was found that could be related to any of the disease phenotypes included. However, three single-nucleotide polymorphisms (SNPs) located in the promoter region (SNP G/C at nt -71 and SNP T/C at nt -189) and in intron 1 (SNP T/G nt 1454) were discovered. Allele frequencies of the SNPs were estimated in a German and Estonian control population and compared to complex I-deficient patients. There was no significant difference between the control population, the LHON patients, or the severely affected patients with complex I deficiency, excluding an association of the polymorphisms with the diseases. Our results suggest that mutations in NDUFA1 do not cause the gender difference observed in clinically severe and complex phenotypes with complex I deficiency.

Leber hereditary optic neuropathy: Does heteroplasmy influence the inheritance and expression of the G11778A mitochondrial DNA mutation?

Leber hereditary optic neuropathy (LHON) is a major cause of inherited blindness in young males. Approximately 1 in 7 individuals with LHON harbor a mixture of mutated and wild-type (normal) mtDNA (heteroplasmy), and the risks of developing blindness in heteroplasmic LHON individuals are not well characterized. MtDNA is inherited exclusively down the maternal line, and although the risks of a relative within a homoplasmic LHON pedigree are relatively well established, the risks of transmission in heteroplasmic LHON pedigrees have not been studied in detail. We analyzed 17 independent pedigrees that harbor the most prevalent LHON mutation: G11778A. The pedigrees were influenced by incomplete ascertainment bias, which was reduced by omitting the affected probands from the analysis. We made the following observations: (1) The frequency of blindness in males was related to the mutation load in that individual's blood. (2) Mothers with < or = 80% mutant mtDNA in blood were less likely to have clinically affected sons than mothers with 100% mutant mtDNA in their blood. (3) Within individual lineages, changes in mutation load from one generation to the next were largely determined by random genetic drift in these pedigrees. This study provides insights into the mutation load, or threshold, necessary for expression of the optic neuropathy, the relationship between mutation load in the mother and the risk of blindness in her children, and the complex inheritance of heteroplasmic mtDNA defects.

Prevalence of mutations causing retinitis pigmentosa and other inherited retinopathies

Inherited retinopathies are a genetically and phenotypically heterogeneous group of diseases affecting approximately one in 2000 individuals worldwide. For the past 10 years, the Laboratory for Molecular Diagnosis of Inherited Eye Diseases (LMDIED) at the University of Texas-Houston Health Science Center has screened subjects ascertained in the United States and Canada for mutations in genes causing dominant and recessive autosomal retinopathies. A combination of single strand conformational analysis (SSCA) and direct sequencing of five genes (rhodopsin, peripherin/RDS, RP1, CRX, and AIPL1) identified the disease-causing mutation in approximately one-third of subjects with autosomal dominant retinitis pigmentosa (adRP) or with autosomal dominant cone-rod dystrophy (adCORD). In addition, the causative mutation was identified in 15% of subjects with Leber congenital amaurosis (LCA). Overall, we report identification of the causative mutation in 105 of 506 (21%) of unrelated subjects (probands) tested; we report five previously unreported mutations in rhodopsin, two in peripherin/RDS, and one previously unreported mutation in the cone-rod homeobox gene, CRX. Based on this large survey, the prevalence of disease-causing mutations in each of these genes within specific disease categories is estimated. These data are useful in estimating the frequency of specific mutations and in selecting individuals and families for mutation-specific studies.

The mitochondrial ND6 gene is a hot spot for mutations that cause Leber's hereditary optic neuropathy

Leber's hereditary optic neuropathy (LHON) is a common cause of bilateral optic nerve disease. The majority of LHON patients harbour one of three point mutations of the mitochondrial DNA (mtDNA) complex I, or NADH:ubiquinone oxidoreductase (ND) genes (G11778A in ND4, G3460A in ND1, T14484C in ND6). As a consequence, screening for these mutations has become part of the routine clinical investigation of young adults who present with bilateral optic neuropathy, and the absence of these mutations is interpreted as indicating there is a low likelihood that an optic neuropathy is LHON. However, there are many individuals who develop the clinical features of LHON but who do not harbour one of these primary LHON mutations. We describe two LHON pedigrees that harbour the same novel point mutation within the mtDNA ND6 gene (A14495G). This mutation was heteroplasmic in both families, and sequencing of the mitochondrial genome confirmed that the mutation arose on two independent occasions. This is the seventh mutation in the ND6 gene that causes optic neuropathy, indicating that this gene is a hot spot for LHON mutations. Protein modelling studies indicate that all of these pathogenic mutations lie within close proximity to one another in a hydrophobic cleft or pocket. This is the first evidence for a relationship between a specific disease phenotype and a specific structural domain within a mitochondrial respiratory chain subunit. These findings suggest that the mtDNA ND6 gene should be sequenced in all patients with LHON who do not harbour one of the three common LHON mutations.

Leber hereditary optic neuropathy associated with antiretroviral therapy for human immunodeficiency virus infection

PURPOSE

Antiretroviral therapy has reduced the morbidity and mortality associated with human immunodeficiency virus (HIV) infection. However, side effects are increasingly recognized, including a commonly reported toxic mitochondrial myopathy. We report such a case of Leber hereditary optic neuropathy in a patient with antiretroviral therapy for HIV infection and speculate on a possible toxic etiologic role in the development of Leber hereditary optic neuropathy by a shared mitochondrial mechanism.

METHODS

Case Report. Bilateral optic disk abnormalities observed in a 38-year-old HIV positive man with a family history of Leber hereditary optic neuropathy were documented with fundus photography, color vision testing, and visual field testing. Mitochondrial DNA testing was used to confirm the genetic predisposition to Leber hereditary optic neuropathy.

RESULTS

Progressive bilateral optic nerve pallor temporally associated with the administration of antiretroviral medication was observed. Diagnostic testing revealed progressive visual field and color vision loss as well as a mitochondrial DNA mutation consistent with Leber hereditary optic neuropathy.

CONCLUSION

Antiretroviral therapy may be associated with the onset of Leber hereditary optic neuropathy in genetically predisposed patients.

Functional analysis of lymphoblast and cybrid mitochondria containing the 3460, 11778, or 14484 Leber's hereditary optic neuropathy mitochondrial DNA mutation

Leber's hereditary optic neuropathy (LHON) is a form of blindness caused by mitochondrial DNA (mtDNA) mutations in complex I genes. We report an extensive biochemical analysis of the mitochondrial defects in lymphoblasts and transmitochondrial cybrids harboring the three most common LHON mutations: 3460A, 11778A, and 14484C. Respiration studies revealed that the 3460A mutation reduced the maximal respiration rate 20-28%, the 11778A mutation 30-36%, and the 14484C mutation 10-15%. The respiration defects of the 3460A and 11778A mutations transferred in cybrid experiments linking these defects to the mtDNA. Complex I enzymatic assays revealed that the 3460A mutation resulted in a 79% reduction in specific activity and the 11778A mutation resulted in a 20% reduction, while the 14484C mutation did not affect the complex I activity. The enzyme defect of the 3460A mutation transferred with the mtDNA in cybrids. Overall, these data support the conclusion that the 3460A and 11778A mutants result in complex I defects and that the 14484C mutation causes a much milder biochemical defect. These studies represent the first direct comparison of oxidative phosphorylation defects among all of the primary LHON mtDNA mutations, thus permitting insight into the underlying pathophysiological mechanism of the disease.

Neuro-ophthalmology of mitochondrial diseases

Polymorphism in mitochondrial DNA necessitates careful scrutiny of potentially pathogenic mutations to establish their true pathogenic significance. Research on Leber hereditary optic neuropathy continues to provide insights into the pathogenesis of mitochondrial disease. Interest in the retinal manifestations of mitochondrial disease has highlighted the macular dystrophy of the 3243 mutation, particularly in association with the syndrome of maternally inherited diabetes and deafness. Mitochondrial encephalopathies present in a number of ways, but imaging predominantly shows abnormalities of myelin and grey-matter nuclei. The mitochondrial myopathies provide insights into interactions between nuclear and mitochondrial DNA mutations and parallels between mitochondrial diseases and aging.

False positive molecular diagnosis of Leber's hereditary optic neuropathy

BACKGROUND

The most common pathogenic mitochondrial DNA (mtDNA) mutation associated with Leber's hereditary optic neuropathy (LHON) is at the 11,778 nucleotide (nt) position and is usually detected by loss of an Sfa NI restriction site. However, Sfa NI restriction site includes five nucleotides. Substitution of any of the five nucleotides leads to loss of the cutting site and causes a false-positive result. We investigated the false-positive diagnosis of LHON by loss of the Sfa NI restriction site using Sfa NI restriction site analysis and single-strand conformation polymorphism (SSCP) analysis.

METHODS

Mae III restriction analysis for double confirmation of the Sfa NI restriction site and direct sequencing for final confirmation of SSCP analysis were performed.

RESULTS

The sensitivity of Sfa NI test was 100% and the specificity of the Sfa NI test was 97%. The false-positive rate of Sfa NI test was 3%. SSCP analysis showed 100% sensitivity. Direct sequencing showed 32 patients had a mutation at nt 11,778 of mtDNA and one patient had a silent mutation at nt 11,782 of mtDNA.

CONCLUSIONS

These results suggest that restriction enzyme digestion analysis requires double confirmation to avoid a false-positive diagnosis and that DNA sequencing is needed for the confirmation of the mutation detected by SSCP.

A case-control study of tobacco and alcohol consumption in Leber hereditary optic neuropathy

PURPOSE

To determine if tobacco or alcohol consumption is associated with vision loss among sibships harboring pathogenic mitochondrial mutations associated with Leber hereditary optic neuropathy.

METHODS

Retrospective case-control study with questionnaires obtained from both affected and unaffected siblings from 80 sibships with Leber hereditary optic neuropathy. Sibships harbored molecularly confirmed mitochondrial DNA mutations at nucleotide positions 11778 (63), 14484 (10), and 3460 (7). Exposure in affected individuals was calculated based on reported consumption before vision loss.

RESULTS

For male probands (67 sibships), the recurrence risk within a sibship was 10.3% (eight of 78) for males and 3.1% (three of 98) for females. For female probands (13 sibships), the recurrence risk within a sibship was 17.6% (three of 17) for males and 0% (zero of 22) for females. Greater risk of vision loss was associated with male sex (odds ratio [OR] = 6.63; 95% confidence interval [CI] = 2.96 to 14.84; P =.00001) and harboring a 3460 or 14484 in comparison with the 11778 mutation (OR = 2.071; 95% CI = 1.19 to 3.58; P =.0095). No significant association of maximal intensity of smoking or cumulative smoking, whether light or heavy, with vision loss was observed. Light (OR = 0. 31; 95% CI = 0.17 to 0.56; P =.0001) and heavy alcohol consumers (OR = 0.25; 95% CI = 0.11 to 0.58; P =.0011) were less likely to be affected than individuals who did not consume alcohol after adjusting for age, sex, and mutation. In a categorical analysis of sibships with the 3460 or 14484 mutation, no relationship of vision loss with tobacco or alcohol consumption was observed.

CONCLUSION

Unlike previous studies, the present study calculated exposure based on self-reported consumption of tobacco or alcohol before vision loss. No significant deleterious association between tobacco or alcohol consumption and vision loss among individuals harboring Leber hereditary optic neuropathy mutations was observed. Tobacco and alcohol do not appear to promote vision loss in Leber hereditary optic neuropathy.

Mitochondrial DNA variant 11719G is a marker for the mtDNA haplogroup cluster HV

Based on sequencing data and results obtained from applying a tailored mismatch polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis, we report that the G allele of the mitochondrial DNA (mtDNA) polymorphism at nucleotide position 11719 is associated with the European mtDNA haplogroup cluster HV, and that 11719A is therefore the ancestral allele.

[Leber optic neuropathy with clinical improvement]

BACKGROUND

Spontaneous recovery in Leber's hereditary optic neuropathy is rare. Does the clinical course of Leber's hereditary optic neuropathy (LHON) differ between patients with and without spontaneous recovery?

MATERIALS AND METHODS

We compared the clinical and molecular genetic characteristics of 12 visually symptomatic patients having the classical clinical course of LHON who recovered spontaneously with those of 60 who did not.

RESULTS

Classical fundus findings and typical visual field defects were comparable in the two groups; vision improved within 18 months in all cases. The worst visual acuity during the acute stage of LHON was 0.03 in the recovery group. Patients with the 3460 and especially the 14484 mutation had a better chance of recovery. No patient with the 11778 mutation who recovered had secondary mutations. Among patients who recovered women were underrepresented and heteroplasmy was more common. Some families showed a raised rate of clinically affected members with recovery.

CONCLUSIONS

The clinical picture of LHON remains the same regardless of whether the patient recovers spontaneously. A higher rate of spontaneous recovery characterizes some families. Spontaneous recovery is rare in women. Heteroplasmy is frequent in patients with recovery. Our results show a better clinical course of LHON in patients with the 11778 mutation without secondary mutations. Prognosis is better if the peripapillary microangiopathy is seen for a relatively long period, and there is only partial optic atrophy.

Microphotometric analysis of NADH-tetrazolium reductase deficiency in fibroblasts of patients with Leber hereditary optic neuropathy

We employed a microphotometric approach to examine whether a defect in the mitochondrial respiratory complex I expected in Leber hereditary optic neuropathy (LHON) as the consequence of a mtDNA (11778G>A) mutation in the ND4 gene coding for a subunit of the respiratory complex I can be detected at the single-cell level. Genetically stable fibroblast cell lines were established from skin biopsies of two members of a Chinese Indonesian family with LHON. The fibroblasts were homoplasmic for the 11778G>A mutation. The activity of the respiratory complex I was examined histochemically by staining for NADH-tetrazolium reductase. The histochemical staining showed a typical pattern with an apparent concentration of the activity around the nucleus, suggested as the reflection of the gradient in the thickness of the unsectioned fibroblast cells. Microphotometric quantification of the staining intensity showed that the activity is linear for at least 60 min. The activity shows a discontinuity in its Arrhenius kinetics with a break point at 13.0-13.5 degrees C (activation energy at 50-58 J/mol and 209-238 J/mol above and below the break temperature, respectively), indicating the membrane association of the NADH-tetrazolium reductase activity. Both patients showed lower fibroblast NADH-tetrazolium reductase activity, with a reduction of degrees 30%. Our results demonstrate the utility of microphotometric analysis in the study of biochemical defects associated with mutations in the mtDNA.

Mutational analysis and clinical correlation in Leber congenital amaurosis

Leber congenital amaurosis (LCA, MIM 204001) is a clinically and genetically heterogeneous retinal disorder characterized by severe visual loss from birth, nystagmus, poor pupillary reflexes, retinal pigmentary or atrophic changes, and a markedly diminished electroretinogram (ERG).

PURPOSE

To examine 100 consecutive patients with LCA in order to assess the relative burden of the three known genes involved in LCA, namely retinal guanylyl cyclase (GUCY2D), retinal pigment epithelium protein ( RPE65), and the cone-rod homeobox (CRX), and to define their clinical correlates.

METHODS

Mutational analysis and detailed clinical examinations were performed in patients diagnosed with LCA at the Johns Hopkins Center for Hereditary Eye Diseases and the Montreal Children's Hospital.

RESULTS

Mutations were identified in 11% of our patients: GUCY2D mutations accounted for 6%, while RPE65 and CRX gene mutations accounted for 3% and 2%, respectively. The clinical presentation was variable; however, the visual evolution in patients with mutations in GUCY2D and CRX remained stable, while individuals with mutations in the RPE65 gene showed progressive visual loss.

CONCLUSIONS

This study suggests that molecular diagnosis of Leber congenital amaurosis could provide important information concerning prognosis and course of treatment.

Novel mutation in RP2 gene in two brothers with X-linked retinitis pigmentosa and mtDNA mutation of leber hereditary optic neuropathy who showed marked differences in clinical severity

PURPOSE

To report the identification of a novel mutation of the RP2 gene in two Japanese brothers with X-linked retinitis pigmentosa of a differing clinical severity. The mother was a carrier of both retinitis pigmentosa and optic atrophy.

METHODS

The older brother had a severe form of retinitis pigmentosa associated with macular degeneration and total optic atrophy, whereas the younger brother presented typical X-linked retinitis pigmentosa.

RESULTS

Each patient exhibited a novel 2-bp insertion at codon 278 in exon 3 of the RP2 gene as well as a 11778 mutation in mitochondrial DNA. This suggests that the older brother may have developed Leber hereditary optic neuropathy as well as retinitis pigmentosa.

CONCLUSION

Molecular testing confirmed the clinical diagnosis in each case. However, such testing did not explain the differences in the severity of the ophthalmoscopic findings between the two brothers.

'Secondary' 4216/ND1 and 13708/ND5 Leber's hereditary optic neuropathy mitochondrial DNA mutations do not further impair in vivo mitochondrial oxidative metabolism when associated with the 11778/ND4 mitochondrial DNA mutation

The pathogenic role of 'secondary' mitochondrial DNA (mtDNA) point mutations, when occurring in patients with Leber's hereditary optic neuropathy (LHON) in association with 'primary' mutations, is still controversial. We used phosphorus magnetic resonance spectroscopy to establish whether two of these 'secondary' LHON mtDNA mutations, 4216/ND1 and 13708/ND5 (haplogroup J), further affect in vivo mitochondrial oxidative metabolism in subjects with the 'primary' 11778/ND4 mtDNA mutation. Brain and skeletal muscle energy metabolism was assessed in 10 subjects homoplasmic for the 11778/ND4 mtDNA mutation and 10 subjects homoplasmic for the same mutation occurring on the haplogroup J mtDNA background. Brain phosphocreatine concentration and phosphorylation potential were significantly reduced and brain inorganic phosphate concentration was significantly increased compared with controls in both groups of 11778/ND4-positive subjects. The degree of reduction in the phosphocreatine concentration and phosphorylation potential and of increase in the inorganic phosphate concentration was, however, similar in the two groups with the 11778/ND4 mtDNA mutation with or without the haplogroup J. Similarly, the rate of muscle phosphocreatine resynthesis after exercise, a sensitive index of the rate of mitochondrial ATP production, was reduced by the same extent in both groups of LHON subjects. This in vivo study does not support synergism of the 4216/ND1 and 13708/ND5 'secondary' mutations with the 11778/ND4 'primary' mutation in determining the deficit of energy metabolism in LHON.

Do idebenone and vitamin therapy shorten the time to achieve visual recovery in Leber hereditary optic neuropathy?

OBJECTIVES

The authors investigated the effectiveness of idebenone combined with vitamin B2 and vitamin C in the treatment of patients with Leber hereditary optic neuropathy (LHON) in an early stage as compared with untreated patients with LHON. These agents may stimulate the formation of ATP.

MATERIALS AND METHODS

For this retrospective study, the authors selected 28 outpatients with LHON from the Keio University Hospital. These patients were followed for 2 to 19 years from disease onset. They were divided into two groups: 14 untreated patients (11778 mutation in 10 patients, 3460 mutation in 2 patients, and 14484 mutation in 2 two patients); and 14 treated patients (11778 mutation in 11 patients, 3460 mutation in 1 patient, and 14484 mutation in 2 patients). The treated patients were administered medical treatment with idebenone, vitamin B2, and vitamin C for at least 1 year. The current study evaluated the following: 1) number of eyes with visual recovery > or = 0.3; 2) interval between the onset of LHON and the beginning of visual recovery; 3) interval between the onset of LHON and visual recovery to 0.3; and 4) interval between the beginning of medical treatment and the beginning of visual recovery in the treated subjects.

RESULTS

There was no significant difference in the number of eyes with visual recovery > or = 0.3 in the two groups with the 3460, 11778, or 14484 mutation. Patients with visual recovery showed a fenestrated scotoma or a clearing of central vision. The mean interval between the onset of LHON and the beginning of visual recovery was significantly shorter in the treated group (11.1 months) than in the untreated group (17.4 months) (P = 0.03). The mean interval between the onset of LHON and visual recovery to 0.3 was significantly shorter in the treated group (17.6 months) than in the untreated group (34.4 months) (P = 0.01). The mean interval between the initiation of medical treatment to the beginning of visual recovery was 5.4 months.

CONCLUSIONS

Results suggest that the administration of idebenone, vitamin B2, and vitamin C sped the recovery of vision in patients with LHON.

Leber's hereditary optic neuropathy mitochondrial DNA mutations at nucleotides 11778 and 3460 in multiple sclerosis

OBJECTIVES

Leber's hereditary optic neuropathy (LHON) can be difficult to distinguish from optic neuritis seen in multiple sclerosis (MS). About half of the LHON patients harbor a mutation at nucleotide (nt) 11778 in the mitochondrial (mt) DNA. In addition, mutations at nt-3460 and nt-14484 have been associated with LHON. An association of LHON and MS has been suspected for decades, and, recently, the LHON nt-11778 and nt-3460 mtDNA mutations have been found in several patients with MS or MS-like disease. We attempted to determine which MS patients should be evaluated further for LHON mutations.

METHODS

We screened 103 clinically definite MS patients (age range from 18 to 72 years, 27 men and 76 women) for the LHON nt-11778 and nt-3460 mtDNA mutations.

RESULTS

Neither mutation was identified in the patients.

CONCLUSIONS

Our findings confirm previous reports which found that both LHON mutations are rare in unselected MS patients. The reports to date suggest that MS patients with peripapillary teleangiectasia typical of LHON, with relatives harboring LHON or with early severe bilateral optic neuropathy, particularly if female, should be further evaluated for LHON mutations.

The epidemiology of pathogenic mitochondrial DNA mutations

During the past decade, there have been many descriptions of patients with neurological disorders due to mitochondrial DNA (mtDNA) mutations, but the extent and spectrum of mtDNA disease in the general population have not yet been defined. Adults with suspected mtDNA disease in the North East of England were referred to a single neurology center for investigation over the 10-year period from 1990 to 1999 inclusive. We defined the genetic defect in these individuals. For the midyear period of 1997, we calculated the minimum point prevalence of mtDNA disease in the adults of working age (> 16-<60 years old for female subjects and <65 years old for male subjects) and the minimum prevalence of adults and children (<60 years for female subjects, <65 years for male subjects) at risk of developing mtDNA disease. mtDNA defects caused disease in 6.57 per 100,000 individuals in the adult population of working age, and 7.59 per 100,000 unaffected adults and children were at risk of developing mtDNA disease. Overall, 12.48 per 100,000 individuals in the adult and child population either had mtDNA disease or were at risk of developing mtDNA disease. These results reflect the minimum prevalence of mtDNA disease and pathogenic mtDNA mutations and demonstrate that pathogenic mtDNA mutations are a common cause of chronic morbidity. These findings have resource implications, particularly for supportive care and genetic counseling.

Spectrum of retGC1 mutations in Leber's congenital amaurosis

Leber's congenital amaurosis (LCA) is the earliest and most severe form of all inherited retinal dystrophies responsible for congenital blindness. Genetic heterogeneity of LCA has been suspected since the report by Waardenburg of normal children born to affected parents. In 1995 we localised the first disease causing gene, LCA1, to chromosome 17p13 and confirmed the genetic heterogeneity. In 1996 we ascribed LCA1 to mutations in the photoreceptor-specific guanylate cyclase gene (retGC1). Here, we report on the screening of the whole coding sequence of the retGC1 gene in 118 patients affected with LCA. We found 22 different mutations in 24 unrelated families originating from various countries of the world. It is worth noting that all retGC1 mutations consistently caused congenital cone-rod dystrophy in our series, confirming the previous genotype-phenotype correlations we were able to establish. RetGC1 is an essential protein implicated in the phototransduction cascade, especially in the recovery of the dark state after the excitation process of photoreceptor cells by light stimulation. We postulate that the retGC1 mutations hinder the restoration of the basal level of cGMP of cone and rod photoreceptor cells, leading to a situation equivalent to consistent light exposure during photoreceptor development, explaining the severity of the visual disorder at birth.