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.

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.

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.