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.

Oval-shaped cornea, lens duplication, and optic nerve hypoplasia associated with myelomeningocele

Oval-shaped cornea associated with true lens duplication and separate capsules is a rare anomaly. It can occur as an isolated finding(1,2) or be associated with other ocular and facial maldevelopments.(3-5) We report a novel association of an hourglass cornea, lens duplication, and optic nerve hypoplasia with myelomeningocele in a male infant.

[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.

[A case of Leber's neuroretinitis]

BACKGROUND

Described in 1916 by Theodore Leber, this rare syndrome characterized by low visual acuity, papillary edema, and a macular star (dry exsudates) occurs classically in the 30 to 40 year age range but also as frequently in children. The visual prognosis is excellent. An infectious cause is found in almost all cases. Case report A 34-year-old man consulted for declining visual acuity of the right eye which began suddenly without pain and was preceded by a flu-like syndrome lasting two weeks. Visual acuity on the right side was 2/10 P6, there was optic disk edema associated with dry macular exsudate (macular star) and a paleness of the posterior pole progressing to the periphery and readily visualized on the angiography, and a central scotome, but no dyschromatopsy. The left eye was strictly normal. Laboratory tests showed an erythrocyte sedimentation rate at 45, C reactive protein at 61, normal red cell count and minimal transaminase elevation. Spinal tap showed: 3 elements/mm(3), protein 0.28g/l, 18% gammaglobulins. Serology tests were negative. Brain imaging was normal.

RESULTS

Corticosteroid flashes for three days were initiated and the patient was seen again two weeks later with clear clinical improvement. Visual acuity was 6/10 P2 with considerable resorption of the edema.

DISCUSSION

This case is a typical illustration of acute Leber's neuroretinititis, probably caused by viral infection. The cerebrospinal fluid tests and brain imaging ruled out multiple sclerosis, and serology tests for syphilis, tuberculosis, Lyme disease and possible parasite infection were negative.

CONCLUSION

Acute lever's neuroretinitis is an uncommon condition which must be distinguished from inflammatory optic neuropathy, particularly in multiple sclerosis which has a very different prognosis and clinical course.

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.

Mutation analysis of 3 genes in patients with Leber congenital amaurosis

OBJECTIVE

To assess the frequency of mutations in the CRX, GUCY2D, and RPE65 genes in patients with Leber congenital amaurosis (LCA).

PATIENTS

One hundred seventy-six probands with a clinical diagnosis of LCA were from 9 countries, with the largest subgroup being 39 probands from India.

METHODS

Samples were screened with single-strand conformation polymorphism analysis followed by DNA sequencing of 3 genes (CRX, GUCY2D, and RPE65) known to be associated with LCA.

RESULTS

Of the 176 probands, 28 (15.9%) harbored possible disease-causing mutations. The relative contribution of each gene to the total number of mutations was as follows: CRX, 2.8%; GUCY2D, 6.3%; and RPE65, 6.8%. No patients who harbored mutations in these genes had associated systemic abnormalities. Molecular diagnosis allowed definitive genetic counseling in a family affected with Best disease and LCA.

CONCLUSIONS

Molecular diagnosis may be of benefit to patients affected with LCA. The relative paucity of mutations found in this study suggests that more LCA-associated genes remain to be discovered.

CLINICAL RELEVANCE

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

[A case of Leber optic neuropathy with a new point mutation in the cytochrome b gene]

BACKGROUND

Leber's hereditary optic neuropathy (LHON) is associated with mutations in the mitochondrial DNA (mtDNA). We report the clinical and molecular genetic findings of a patient who does not carry any of the common LHON mutations.

METHODS

Clinical data were collected for the affected patient and two unaffected maternal family members. Complete sequence analysis of the mtDNA protein coding region was performed in the affected patient.

RESULTS

Clinical examination of the affected patient showed typical features of LHON. A nucleotide exchange was detected at np14894 replacing an evolutionarily conserved phenylalanine by a leucine in the cytochrome b gene. The mutation was also present in two unaffected maternal family members, but absent in 60 other LHON lineages and 175 unrelated controls.

CONCLUSIONS

Cytochrome b plays an important role in the electron transport chain of mitochondrial oxidative phosphorylation, and some mutations in the gene encoding cytochrome b have been associated with LHON. Our results may imply that the novel mutation at np14894 is responsible for LHON in this family.

Optic nerve enhancement on magnetic resonance imaging in arteritic ischemic optic neuropathy

Although optic nerve enhancement may be seen in magnetic resonance imaging of radiation-induced ischemic optic neuropathy, similar enhancement in ischemic optic neuropathy has not been previously reported in the English-language neuroophthalmologic literature. We report three cases of optic nerve enhancement in biopsy-proven arteritic ischemic optic neuropathy. Clinicians should consider giant cell arteritis in the differential diagnosis of an optic neuropathy with optic nerve enhancement on magnetic resonance imaging.

Optic nerve enhancement on orbital magnetic resonance imaging in Leber's hereditary optic neuropathy

An 18-year-old man with Leber's hereditary optic neuropathy and bilateral visual loss had optic nerve enhancement on T1-weighted orbital fat-suppressed magnetic resonance imaging. To our knowledge, this is the first reported case of optic nerve enhancement on orbital magnetic resonance imaging in Leber's hereditary optic neuropathy.

[Leber optic neuropathy in women and children]

BACKGROUND

Leber's hereditary optic neuropathy is associated with point mutations in the mitochondrial DNA (mtDNA) that appear to be pathogenetic for this disease. These mutations affect nucleotide positions 3460, 11778 and 14484. Does the clinical course of LHON differ between men, women and children?

MATERIALS AND METHODS

We reviewed the clinical and molecular genetic characteristics of 15 visually symptomatic patients with the clinical diagnosis of LHON (11 women and 4 male children) and compared them with 66 men with LHON.

RESULTS

LHON was confirmed clinically and with molecular genetic methods in all cases. Men, women and children showed no differences: Classic fundus findings and typical visual field defects were equally found in both sexes. However, age at the beginning of the disease, severity of LHON and rate of spontaneous recovery differed between groups. Women were older (19-55 years, average 31.3 years) than men (15-53 years, average 24.3 years) at the beginning of the disease. Women suffered more severely from LHON. Spontaneous recovery of vision in women was extremely rare. Many more women had a LHON-affected mother than men. All the affected children (9-14, average 11.7 years at the beginning of the disease) did not have a good visual outcome.

CONCLUSIONS

There are some differences in the course of LHON between men and women, concerning age, severity of LHON and rate of spontaneous recovery. Children may also have an unfavorable prognosis.

[Leber's hereditary optic nerve neuropathy]

The authors present a case report of 26 years old man with bilateral optic nerve neuropathy. Detection of heteroplasmic mutation of mitochondrial DNA at G3460A site confirmed the suspicion on Lebers hereditary optic nerve neuropathy (LHON). Genetic and environmental factors of the disease and various accompanying neurologic and other symptoms, which can together with the optic nerve defect participate in the development of of the LOHN clinical pattern are discussed. (Ref. 12.)

Leber's hereditary optic neuropathy

A case of Leber's hereditary optic neuropathy (LHON) in a healthy young man who presented with a slow progressive visual loss in one eye and later developed a visual loss in the other eye. There was no pre-existing symptom and no history of visual loss in other family members. Mitochondrial DNA mutation at 11,778 was found in the patient and his uneffected mother and brother. Currently the availability of reliable molecular genetic testing has revolutionized the diagnosis of LHON. LHON is a maternal inherited disorder that causes bilateral visual loss, predominantly in young men. This disorder has been associated with point mutations in the mitochondrial genome which constitute the different clinical phenotypes and prognosis. Genetic counseling in families at risk is recommended.

Ocular and oculomotor signs in Joubert syndrome

A number of oculomotor defects have been described in Joubert syndrome. This study systematically examined the oculomotor systems of 13 individuals previously diagnosed with Joubert syndrome. Twelve had the characteristic "molar tooth sign" seen on magnetic resonance imaging scan. In all individuals, smooth pursuit gain and vestibulo-ocular reflex cancellation were decreased in the horizontal and vertical directions and volitional saccades, when generated, were hypometric. We believe that these defects arise from a disorder in the posterior cerebellar vermis. All individuals also had partial to complete oculomotor apraxia in which initiation of saccades was prolonged or impaired. The oculomotor apraxia in Joubert syndrome differs from congenital idiopathic oculomotor apraxia in that both volitional saccades and quick phases of nystagmus were impaired both in the horizontal and vertical directions, and the defects did not resolve with time. We believe that the oculomotor apraxia arises from a disorder involving the projections from the superior colliculus to the parapontine reticular formation and rostral interstitial nucleus of the medial longitudinal fasciculus. A subset of individuals also had severe visual loss, pendular nystagmus, pigmentary changes in the fundus, and decreased vestibulo-ocular reflexes. We believe that this is a form of Leber's amaurosis occasionally associated with Joubert syndrome. In summary, key oculomotor features of Joubert syndrome are decreased smooth pursuit and vestibulo-ocular reflex cancellation, partial to complete oculomotor apraxia both in the horizontal and vertical directions, and hypometric saccades if oculomotor apraxia is not complete.

[Clinical manifestation and molecular identification of patients with Leber's hereditary optic neuropathy in a national reference center for neuro-ophthalmology in Cuba]

INTRODUCTION

Leber's hereditary optic neuropathy (LHON) is a mitochondrial disorder, confirmed at a molecular level 10 years ago. This had permitted better understanding of the condition. Since 1998, the Instituto de Neurología y Neurocirugía has used these techniques for the study of mutations which are considered to be the origin of the disorder.

PATIENTS AND METHODS

We describe the characteristics of 14 cases from 10 families with LHON and the molecular confirmation found between 1994 and 1998 in the Instituto de Neurología Neurocirugía de Cuba. We also review the few cases seen in the previous 18 years. These were from only two families. They were diagnosed on clinical grounds and in view of maternal inheritance.

RESULTS AND CONCLUSIONS

In 80% of the families in which the presence of primary mutations was investigated there was A117789, and in 20% A3460G. The average age of appearance was 28 years. The ages of onset were within the limits of 11 years and 48 years. There were 43% women. Two cases were considered to be sporadic. The clinical features corresponded to those described in such cases, with severe visual defects, central scotomas, very reduced colour vision and severely altered visual evoked potentials, with normal diffuse light and pattern electroretinograms. An improvement in visual acuity of 0.2 was seen in two cases. Microangiopathy, described as characteristic of the early stages of this disorder was detected in five cases, in at least one eye. The others had different degrees of optic atrophy. Two generations of one complete family, all with mutation 3460, were studied. In several families with this mutation alterations were found in the colour vision test of Farnsworth Munsell Hue 100 and also microangiospathy of the retina.

Update on hereditary optic neuropathy

Although no treatment is available for hereditary optic neuropathies, recent localization and identification of some of the genetic loci have helped the evaluation and management of patients with these disorders. This article discusses the clinical features and known genetic information regarding Leber's hereditary optic neuropathy, dominant optic atrophy, recessive optic atrophy, and Wolfram syndrome.

Leber's hereditary optic neuropathy mitochondrial DNA mutations in familial multiple sclerosis

Leber's hereditary optic neuropathy (LHON) can be difficult to distinguish from optic neuritis due to multiple sclerosis (MS). For several decades an association of LHON and MS has been suspected, and within the past 7 years the LHON nucleotide (nt)-3460 and nt-11778 mtDNA mutations have been identified in several patients with MS-like phenotypes. To further study this association, we tested 42 index patients with clinically definite, familial MS for the LHON mtDNA mutations at nt-3460, nt-11778, and nt-14484. No patients had a pathogenic LHON mtDNA mutation; however, two MS patients with unilateral optic neuritis harbored the nt-15257 mtDNA polymorphism that was reported originally as a pathogenic LHON mutation. Several investigators have shown evidence that the nt-15257 mtDNA mutation is not primarily pathogenic. Therefore, we conclude that pathogenic LHON mtDNA mutations are absent or rare in unselected patients with familial, clinically definite MS (95% confidence intervals for each of the negative mutations 0-7.0%).

[An analysis of 6 Leber mutations in 31 individuals with optic atrophy. A study of its transmission in 5 families]

BACKGROUND

Leber's hereditary optic neuropathy (LHON) is a mitochondrial disorder that represents the most frequent cause of visual loss among otherwise healthy young men.

PATIENTS AND METHODS

We have screened for the most important LHON mutations (primary mutations) and several other previously described mutations (secondary mutations) in 31 Spanish patients suffering from optic atrophy. These individuals fulfilled the clinical criteria for LHON. We have compared the mutation frequencies obtained with those reported in several other countries. We have also followed the segregation of the disease and its associated LHON mutations in five families. The screening has been performed by PCR followed by restriction enzyme digestions and electrophoretic separation.

RESULTS

67.75% of the patients did not harbour any of the studied mutations, whereas 16.13% showed one mutation and the remaining 16.13% carried two Leber mutations in their mitochondrial DNA. The three primary mutations as well as G15257A were the changes most frequently detected (30% each of them). There were no significant differences among the compared populations in terms of frequencies of the primary mutations. In contrast, our patients showed a significantly higher rate of 15257 mutation.

CONCLUSIONS

The incidence of primary LHON mutations among the Spanish patients is not statistically different from those observed in other Caucasian populations. Transmission of the mutation to the progeny is not necessarily linked to the transmission of the disease. This fact complicates genetic counselling and makes prenatal diagnosis almost impossible for this disease.

A multiple sclerosis-like illness in a man harboring the mtDNA 14484 mutation

In most cases of Leber's hereditary optic neuropathy (LHON) the only clinical manifestation is visual loss. A multiple sclerosis-like illness has been infrequently reported in association with LHON. Most patients are women harboring the mtDNA 11778 mutation. We present a young man with clinical and paraclinical evidence of a demyelinating process with profound bilateral visual loss who harbored the mtDNA 14484 mutation associated with LHON.

Dominant optic atrophy. Refining the clinical diagnostic criteria in light of genetic linkage studies

OBJECTIVE

To describe the clinical findings and refine the clinical diagnostic criteria for dominant optic atrophy based on eight British families in which the diagnosis was confirmed by linkage analysis.

DESIGN AND PARTICIPANTS

Case series; 92 subjects in 8 pedigrees had both eyes examined.

INTERVENTION

Family members received a domiciliary examination based on best-corrected visual acuity, color vision using Ishihara and Hardy Richter Rand (HRR) plates, confrontation field testing using a red target, and optic disc evaluation using a direct ophthalmoscope. Genomic DNA was extracted from leukocytes or buccal mucosal cells and genotyped using 12 fluorescently labeled microsatellite markers from the region 3q27-q29.

MAIN OUTCOME MEASURES

Subjects were classified clinically as definitely or possibly affected on the basis of the domiciliary examination before genetic analysis, and these results were compared with the haplotype analysis.

RESULTS

Clinically, 43 subjects were identified as definitely affected, 4 as possibly affected, and 45 as unaffected. Visual acuity in affected subjects ranged from 6/6 to count fingers and declined with age. On genetic analysis, a haplotype was identified in each family, which was found in all definitely affected members but not in those regarded as unaffected. The four possibly affected individuals also bore the haplotype that segregated with the disease.

CONCLUSIONS

Simple clinical tests are highly efficacious in diagnosing dominant optic atrophy. Contrary to accepted criteria, symptoms begin before the age of 10 years in only 58% of affected individuals. Visual acuity in affected subjects is highly variable. A mild degree of temporal or diffuse pallor of the optic disc and minimal color vision defects, in the context of a family with dominant optic atrophy, are highly suggestive of an individual being affected, even if the visual acuity is normal. This widens the generally accepted diagnostic criteria for this disease.