Quantitative determination of heteroplasmy in Leber's hereditary optic neuropathy by single-strand conformation polymorphism.

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Abstract

PURPOSE: The maternal inheritance of Leber's hereditary optic neuropathy (LHON) is caused by defects in the genes of mitochondrial DNA (mtDNA). The most prevalent mtDNA mutation, present in 40% to 90% of families with this disease, is a G to A substitution at nucleotide position 11778. The rapid and accurate quantification of heteroplasmy of this mutation will help determine the relative risk for disease expression. METHODS: The authors conducted screening tests for heteroplasmy in 44 visually affected patients with the 11778 mutation and 34 unaffected members of 36 Japanese families with LHON using the single-strand conformation polymorphism analysis. This method can detect even a single base difference between the sequences of wild type and mutant DNA strands. The percentage of mutant mtDNA was calculated using an image analyzer. RESULTS: Single-strand conformation polymorphism analysis allowed the detection of heteroplasmy ranging from 5% to 95%. Five (14%) of the 36 families showed heteroplasmy, and 14 (18%) of the 78 persons tested had heteroplasmy ranging from 10% to 94%. Seven patients with heteroplasmy with visual loss had mutant mtDNA ranging from 62% to 94%. CONCLUSIONS: Single-strand conformation polymorphism analysis is rapid, efficient, and accurate for detecting point mutations and quantifying heteroplasmy in mtDNA. Individuals with heteroplasmy with less than 60% of mutant mtDNA in circulating leukocytes are probably at lesser risk for developing optic atrophy.