Eeva Nikoskelainen

Clinical expression of Leber hereditary optic neuropathy is affected by the mitochondrial DNA-haplogroup background.

Leber hereditary optic neuropathy (LHON) is due primarily to one of three common point mutations of mitochondrial DNA (mtDNA), but the incomplete penetrance implicates additional genetic or environmental factors in the pathophysiology of the disorder. Both the 11778G-->A and 14484T-->C LHON mutations are preferentially found on a specific mtDNA genetic background, but 3460G-->A is not. However, there is no clear evidence that any background influences clinical penetrance in any of these mutations. By studying 3,613 subjects from 159 LHON-affected pedigrees, we show that the risk of visual failure is greater when the 11778G-->A or 14484T-->C mutations are present in specific subgroups of haplogroup J (J2 for 11778G-->A and J1 for 14484T-->C) and when the 3460G-->A mutation is present in haplogroup K. By contrast, the risk of visual failure is significantly less when 11778G-->A occurs in haplogroup H. Substitutions on MTCYB provide an explanation for these findings, which demonstrate that common genetic variants have a marked effect on the expression of an ostensibly monogenic mtDNA disorder.

Vigabatrin, a gabaergic antiepileptic drug, causes concentric visual field defects

Objective: To determine whether there is a causal link between vigabatrin treatment and concentric visual field defects and to evaluate the prevalence of these visual field constrictions. Background: While the GABAergic antiepileptic drug (AED) vigabatrin was being clinically developed, only rare cases (less than 1:1000) of symptomatic visual field constriction and retinal disorders were reported. During 1997 to 1998, concentric visual field constrictions were described in case reports of mostly drug-resistant epilepsy patients receiving vigabatrin concurrently with other AEDs. Methods: Ophthalmologic tests including Goldmann perimetry were performed on 32 adult patients on long-term successful vigabatrin monotherapy (treatment duration 29 to 119 months) and on 18 patients on carbamazepine monotherapy (treatment duration 32 to 108 months). Eighteen healthy adults served as controls. Results: None of the patients complained about vision problems when asked to participate into the study. Thirteen out of the 32 (40%) epilepsy patients treated with vigabatrin monotherapy had concentrically constricted visual fields (9% severely, 31% mildly constricted), whereas none of the carbamazepine monotherapy patients or normal controls presented with a visual field defect (chi-square test, p = 0.0001). The extents of the visual fields were significantly constricted in vigabatrin group as compared with the visual fields of the patients in carbamazepine group or healthy controls (analysis of variance, Scheffé F-test, significant at 99%). Conclusions: The use of vigabatrin seems to increase the risk of a unique and specific pattern of bilateral, mainly asymptomatic visual field constriction. This risk should be considered when using vigabatrin. Visual field testing should also be performed before treatment and during routine follow-up for patients on vigabatrin.

Electron transfer properties of NADH: Ubiquinone reductase in the ND1/3460 and the ND4/11778 mutations of the Leber hereditary optic neuroretinopathy (LHON)

We report the electron transfer properties of the NADH: ubiquinone oxidoreductase complex of the respiratory chain (Complex I) in mitochondria of cells derived from LHON patients with two different mutations in mitochondrial DNA (mtDNA). The mutations occur in the mtDNA genes coding for the ND1 and ND4 subunits of Complex I. TheNDI/3460 mutation exhibits 80% reduction in rotenone‐sensitive and ubiquinone‐dependent electron transfer activity, whereas the proximal NADH dehydrogenase activity of the Complex is unaffected. This is in accordance with the proposal that the ND1 subunit interacts with rotenone and ubiquinone. In contrast, theND4/11778 mutation had no effect on electron transfer activity of the Complex in inner mitochondrial membrane preparations: alsoK m for NADH and NADH dehydrogenase activity were unaffected. However, in isolated mitochondria with theND4 mutation, the rate of oxidation of NAD‐linked substrates, but not of succinate, was significantly decreased. This suggests that the ND4 subunit might be involved in specific aggregation of NADH‐dependent dehydrogenases and Complex I, which may result in fast (‘solid state’) electron transfer from the former to the latter.

Ophthalmologic Findings in Leber Hereditary Optic Neuropathy, with Special Reference to mtDNA Mutations

BACKGROUND Leber hereditary optic neuropathy (LHON) is associated with primary and secondary mutations in mitochondrial DNA. Clinical studies suggest that there is a wide spectrum of clinical expression. METHODS Fifty-three affected and 131 unaffected maternal relatives from 21 pedigrees with LHON were studied neuro-ophthalmologically and followed over a period of 14 years. Mitochondrial DNA analysis was performed on their blood specimens. RESULTS Thirty-two affected (60%) individuals from ten families harbored the 11778 mutation and ten individuals (19%) from three families harbored the 3460 mutation. No confirmed primary mutation was detected in 11 (21%) affected individuals from eight families. The visual outcome was better in families with the 3460 mutation than in those with the 11778 mutation. Secondary mutations did not affect the penetrance or the visual outcome. Fifteen patients had a favorable outcome; seven of whom had subclinical disease, two had slowly progressive LHON with a favorable visual outcome, and six had classic LHON with spontaneous recovery. In seven patients, the onset of the disease had been in childhood. These patients had a more favorable prognosis than the adults. Results of eye examinations of asymptomatic maternal relatives showed subclinically affected individuals. CONCLUSIONS In addition to classic LHON, the disease can manifest itself in three different atypical forms: subclinical disease, slowly progressive LHON with a favorable visual outcome, and LHON with the classic acute stage but spontaneous visual recovery. The current study suggests that the ophthalmologic findings and outcome in LHON are independent of secondary mutations.

Identification of an X-Chromosomal Locus and Haplotype Modulating the Phenotype of a Mitochondrial DNA Disorder

Mitochondrial DNA (mtDNA) mutations are a major cause of human disease. A large number of different molecular defects ultimately compromise oxidative phosphorylation, but it is not clear why the same biochemical defect can cause diverse clinical phenotypes. There is emerging evidence that nuclear genes modulate the phenotype of primary mtDNA disorders. Here, we define an X-chromosomal haplotype that interacts with specific MTND mutations to cause visual failure in the most common mtDNA disease, Leber hereditary optic neuropathy. This effect is independent of the mtDNA genetic background and explains the variable penetrance and sex bias that characterizes this disorder.

Epidemiology and penetrance of Leber hereditary optic neuropathy in Finland

We have performed an entire-population-based survey of the epidemiology and penetrance of Leber hereditary optic neuropathy (LHON) in Finland – a country that is among the best-studied genetic isolates in the world. During our long-term clinical follow-up period since 1970, we have so far identified 36 LHON families in Finland, comprised of almost 1000 family members. Counting the unaffected family members has been possible thanks to accessible genealogical records, and this has improved the accuracy of our penetrance figures by minimizing the sample bias. Our results, although confirming some well-known features of LHON, indicate that the overall penetrance of LHON is lower than previously estimated, and that affected females have a higher incidence of affected offspring compared to the unaffected females. The prevalence of LHON in Finland is 1:50 000, and one in 9000 Finns is a carrier of one of the three LHON primary mutations.

Ophthalmologic findings in long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency caused by the G1528C mutation : A new type of hereditary metabolic chorioretinopathy

OBJECTIVE The purpose of the study was to determine the nature and course of ophthalmic abnormalities in long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency, a recently discovered disorder of mitochondrial fatty acid beta-oxidation. STUDY DESIGN The study design was a cohort (case series). PARTICIPANTS A retrospective review of the records of 15 children who had died during their first 2 years was performed. Also performed were a longitudinal reanalysis and cross-sectional clinical examination of four long-term survivors aged 5 to 31 years. MAIN OUTCOME MEASURES Visual acuity, refraction, visual fields, ophthalmoscopy, fluorescein angiography, biometry, corneal topography, electroretinography (ERG), visual-evoked potentials (VEPs), color vision, and dark adaptation were measured. RESULTS In seven children, ophthalmoscopic findings were within normal limits at 3 days to 13 months of age (median, 4.8 months). In 11 children, a granular retinal pigment epithelium (RPE), with or without pigment clumping in the macula, was seen at 4 months to 5 years of age (median, 9 months). Two long-term survivors, 16 and 31 years of age, eventually had circumscribed atrophy of the choroid, RPE, and retina, which coincided with a posterior staphyloma type 1. They had progressive axial myopia starting at 6 and 12 years of age and later paracentral scotomas leading to poor central vision. They suffered from early difficulty with mesopic vision, glare, and a severe generalized color vision deficiency that started as a tritanomaly. A third survivor was mildly myopic at 5 years of age. All four surviving patients had visually insignificant, flake-like supranuclear opacities in the lens. The ERG initially was normal but deteriorated during the first decade and later was unrecordable. The VEP responses remained fairly normal. Initially, angiography showed no blockade of the choroidal fluorescence because of the thin RPE. Filling of choroidal vessels was delayed, and the choriocapillaris and, later, larger choroidal vessels in the posterior pole became nonperfused. CONCLUSIONS In LCHAD deficiency, the fundus is normal at birth (stage 1). Soon, however, pigment dispersion occurs in the RPE (stage 2), followed by circumscribed chorioretinal atrophy, occlusion of choroidal vessels, and deterioration of central vision, often with relative sparing of the peripheral fundus (stage 3). Finally, posterior staphylomas and central scotomas may develop (stage 4). Developmental cataract, progressive myopia, and deterioration of visual fields and color vision are new findings in LCHAD deficiency. The chorioretinopathy and abnormal ERG precede the development of myopia and posterior staphyloma, which, in turn, coincide with the loss of macular vision. The authors postulate that the RPE or choriocapillaris is primarily affected. Awareness of the characteristic ocular features is important because of an opportunity for dietary treatment, genetic counseling, and prenatal diagnosis.

The spectrum of mitochondrial DNA mutations in families with Leber hereditary optic neuroretinopathy.

The mitochondrial complex I genes were sequenced in seven Leber hereditary optic neuroretinopathy (LHON) families without the ND4/11778 and ND1/3460 mutations. Four replacement mutations restricted only to LHON families were found, one in the ND1 gene at nt 4025, and three in the ND5 gene at nt 12811, 13637, and 13967. The mutations did not change evolutionarily conserved amino acids suggesting that they are not primary LHON mutations in these families. They may be considered as secondary LHON mutations serving as exacerbating factors in an appropriate genetic background. A complex III mutation, cyt b/15257, has been suggested to be one of the primary mutations causing LHON. Its presence was determined for 23 Finnish LHON families, and it was detected in two families harboring the ND4/11778 mutation. Similarly, complex IV mutation COI/7444 was screened in Finnish LHON families, and it was found in one family carrying the ND1/3460 mutation.

New aspects of the genetic, etiologic, and clinical puzzle of Leber's disease.

Joint World Meeting in Neuro-Ophthalmology, May 14-18,1984, Antwerp, Belgium. 19. Nikoskelainen E, Hoyt WF, Nummelin K. Ophthalmoscopic findings in Leber’s hereditary optic neuropathy. I. Fundus findings in asymptomatic family members. Arch Ophthalmol 20. Carroll WM, Mastaglia FL. Leber’s optic neuropathy: a clinical and visual evoked potential study of affected and asymptomat ic members of a six-generation family. Brain 21. Stehouwer A, Oosterhuis JA, Renger-Van Dijk AH, Went LN. Leber’s optic neuropathy. 11. Fluorescein angiographic studies. Doc Ophthalmol 1982;53:113-22. 22. Nikoskelainen E, Hoyt WF, Nummelin K. Fundus findings in Leber’s hereditary optic neuroretinopathy. 111. Fluorescein angiographic studies. Arch Ophthalmol 1984;102:981-9. 23. Stehouwer A, Went LN. Leber’s optic nedopathy. I. Clinical studies. Doc Ophthalmol 1982;53:97-111. 24. Livingstone JR, Mastaglia FL, Howe JW, Aherne GES. Leber’s optic neuropathy: clinical and visual evoked response studies in asymptomatic and symptomatic members of a 4generation family. Br J Ophthalmol 1980;64751-7. 1970;89:125-46.

Human mitochondrial DNA types in Finland

SummaryVariation in mitochondrial DNA (mtDNA) in a sample of 110 Finns was analyzed with six restriction enzymes, AvaII, BamHI, HaeII, HinII, HpaI, and MspI, by using total blood cell DNA probed with mouse mtDNA. Two new enzyme morphs were observed, one for HaeII and one for HindII. Double-digestion experiments indicated that the BamHI morphs 2 and 3 result from base changes leading to AvaII morphs 3 and 9, respectively. Of the ten different mtDNA types observed, defined by restriction fragment patterns, seven have been previously described in Caucasoid populations. The three new “Finnish” mtDNA types can be derived from Caucasoid lineages by single restriction site changes. The results were used to reconstruct a phylogenetic tree for Caucasoid mtDNA types defined by the enzymes used. The frequencies of mtDNA types were used to compute genetic distances between Finns, Italians, and Israeli Jews. The frequencies of both enzyme morphs and mtDNA types show that the Finnish population is highly homogeneous.