Neurological symptoms and natural course of xeroderma pigmentosum.

We have prospectively followed 16 Finnish xeroderma pigmentosum (XP) patients for up to 23 years. Seven patients were assigned by complementation analysis to the group XP-A, two patients to the XP-C group and one patient to the XP-G group. Six of the seven XP-A patients had the identical mutation (Arg228Ter) and the seventh patient had a different mutation (G283A). Further patients were assigned to complementation groups on the basis of their consanguinity to an XP patient with a known complementation group. The first sign of the disease in all the cases was severe sunburn with minimal sun exposure in early infancy. However, at the time the diagnosis was made in only two cases. The XP-A patients developed neurological and cognitive dysfunction in childhood. The neurological disease advanced in an orderly fashion through its successive stages, finally affecting the whole nervous system and leading to death before the age of 40 years. Dermatological and ocular damage of the XP-A patients tended to be limited. The two XP-C patients were neurologically and cognitively intact despite mild brain atrophy as seen by neuroimaging. The XP-G patients had sensorineural hearing loss, laryngeal dystonia and peripheral neuropathy. The XP-C patients had severe skin and ocular malignancies that first presented at pre-school age. They also showed immunosuppression in cell-mediated immunity. Neurological disease appears to be associated with the complementation group and the failure of fibroblasts to recover RNA synthesis following UV irradiation, but not necessarily to the severity of the dermatological symptoms, the hypersensitivity of fibroblasts to UVB killing or the susceptibility of keratinocytes to UVB-induced apoptosis.

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.

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 cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy: a cross-sectional study.

OBJECTIVE: To determine the ophthalmologic findings, especially the nature of retinal vascular changes, and their clinical significance in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), a disease that causes migraine, recurrent strokes, and finally subcortical vascular dementia. DESIGN: Cross-sectional study. PARTICIPANTS: Thirty-eight CADASIL patients (19 to 61 years old; 20 in a prestroke group, 15 in a stroke group, and 3 in a dementia group), all with the R133C NOTCH3 mutation and including one homozygous patient, underwent a detailed ophthalmologic examination. METHODS: Common cardiovascular risk factors were evaluated. Ophthalmologic examination included best-corrected visual acuity, anterior- and posterior-segment biomicroscopy, and measurement of intraocular pressure. In 33 patients and 16 healthy controls (20-64 years old), retinal fundus photographs were taken. Diameters of all arterioles and venules located in the area from 0.5 to 1.0 disc diameters from the optic disc margin were measured with a computer-based program and arteriole-to-venule (A/V) ratios were calculated from digitized photographs. RESULTS: General arterial narrowing and arteriovenous nickings were common. Straightening of the retinal arterioles and a marked wall reflex (n = 6) occurred. The A/V ratio of CADASIL patients was significantly (P< 0.001) lower than that of controls. One patient had one retinal microinfarct and hemorrhages. The homozygous patient had a chorioretinal scar as a sign of circulatory deficiency. Anterior-segment changes included mild iris atrophy (n = 5) and various degrees of lens opacities. Visual acuity was normal in all but 2 patients, who had cataract and amblyopia. CONCLUSIONS: The generalized arteriopathy of CADASIL causes a wide variety of changes in retinal arterioles but only minimal functional disturbances. These findings are consistent with alterations in arterioles in the cerebral cortex with which the retina and its arterioles are analogous, but contrast with the severe damage of cerebral white matter arterioles.

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.

Nordic research in ophthalmology.

Nordic ophthalmologists and vision scientists are active in many fields of eye research. This is most evident at the biannual Nordic Congress of Ophthalmology, most recently held in Malmö in June 2004. The authors here review some of the research in vision and ophthalmology presented at this meeting or published recently by Nordic scientists. This paper does not represent a comprehensive review of all Nordic research in the field, but attempts to give an overview of some of the activities underway in eye research in this part of the world.

Dominant optic atrophy: correlation between clinical and molecular genetic studies.

PURPOSE: To assess the clinical picture and molecular genetics of 14 Finnish families with dominant optic atrophy (DOA). METHODS: The clinical status of family members was based on the assessment of visual acuity, colour vision, visual fields and optic nerve appearance; 31 individuals were affected, two suspect and 21 unaffected. A total of 30 coding exons and exon- intron boundaries of the OPA1 gene were sequenced in order to detect mutations. RESULTS: Half the patients were diagnosed at the age of < or = 20 years. Ten out of 20 affected individuals followed up for > or = 6 years had a progressive disease and 10 had a stable disease. According to WHO criteria, 36% of the affected patients were visually handicapped. Eight OPA1 pathogenic mutations, all but one novel, and 18 neutral polymorphisms were detected. CONCLUSION: The most sensitive indicators of DOA were optic disc pallor and dyschromatopsia. With molecular genetic analysis, asymptomatic mutation carriers and DOA cases with a mild clinical outcome were ascertained. No mutational hotspot or Finnish major mutation in the OPA1 gene could be demonstrated as most families carried a unique mutation. No obvious genotype- phenotype correlation could be detected. Detailed clinical assessment and exclusion of non-DOA families prior to mutation screening are necessary for obtaining a high mutation detection rate.

Scanning laser Doppler flowmetry shows reduced retinal capillary blood flow in CADASIL.

BACKGROUND AND PURPOSE: Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a progressive systemic nonatherosclerotic angiopathy which causes ischemic strokes and vascular subcortical dementia. A cross-sectional study was performed to examine the retinal vascular caliber and blood flow in CADASIL. METHODS: Scanning laser Doppler flowmetry was used in a case-control study (11 patients and controls) of peripapillary retinal circulation. Automated full-field perfusion image analysis was used to analyze the flow data. Retinal vessel calibers were measured from retinal images acquired with scanning laser ophthalmoscopy. The caliber of the superior and inferior temporal retinal artery and vein were measured 1 and 2 mm from the disc rim, and the mean values were used for analysis. RESULTS: Retinal capillary peak systolic flow (mean, 249 versus 311 arbitrary unit [AU]; P=0.072) was lower, and mean capillary flow (mean, 184 versus 224 AU; P=0.12) and minimum diastolic flow (mean, 105 versus 132 AU; P=0.16) tended to be lower in patients than in controls. No significant difference in the calibers of proximal retinal arteries (mean, 104 versus 108 microm) and veins (mean, 150 versus 145 microm) was found between the patients and controls. CONCLUSIONS: Retinal capillary blood flow is mild to moderately reduced in CADASIL but that does not appear to cause major ischemic injury. Such reduction is analogous to that in the cerebral cortex in CADASIL patients with which retina appears to share its relative sparing from severe arterial ischemic tissue damage.

Segregation of the ND4/11778 and the ND1/3460 mutations in four heteroplasmic LHON families.

Leber hereditary optic neuropathy (LHON) is an ocular disease associated with mutations in the mitochondrial DNA (mtDNA). The level of heteroplasmy in the mtDNA mutations ND4/11778 and ND1/3460 was followed over a period of 4-12 years in blood samples taken from nine members of four heteroplasmic LHON families. In addition, hair follicle and urinary tract epithelium samples of one individual were studied. The quantification of heteroplasmy was performed using the solid-phase minisequencing method. Only minor and random shifts in the heteroplasmy levels were observed over time, but there were no systematic changes towards an increasing or decreasing proportion of either LHON mutant in the individuals. This indicates that there is no selection for either mtDNA genotype but the segregation of the wild-type mtDNAs and those carrying LHON mutations is a stochastic process governed by random genetic drift. In this respect, LHON mutations seem to behave like neutral polymorphisms.

Genetic counseling in Leber hereditary optic neuropathy (LHON).

PURPOSE: To demonstrate the importance of mitochondrial DNA (mtDNA) analysis in the diagnosis of Leber hereditary optic neuropathy (LHON) and illustrate the difficulties in genetic counseling of the disease. PARTICIPANTS AND METHODS: Ophthalmological and molecular genetic study of one affected and three unaffected members from a family with heteroplasmic ND1/3460 mtDNA mutation associated with LHON. RESULTS: The proband had variable amounts of mutant mtDNA in all his tissues studied, ranging from 58% in blood to 92% in subcutis. The mother had an extremely low amount of mutant mtDNA in her tissues, except for hair roots, which contained only normal mtDNA. No mutant mtDNA could be detected in the proband's unaffected sister and maternal aunt. CONCLUSIONS: Despite her minimal mutation load, the mother of the proband has still transmitted a considerable amount of mutant mtDNA to her son, who is severely affected. Although proband's unaffected sister and maternal aunt had no mutant mtDNA, a theoretical risk that they may transmit the disease to their offspring cannot be excluded.