DNA, MitochondrialMutationPoint MutationMitochondrial DiseasesOptic Atrophy, Hereditary, LeberMELAS SyndromeMitochondrial MyopathiesMutation, MissenseOptic Atrophies, HereditaryMitochondrial EncephalomyopathiesRNA, Transfer, LeuGenome, MitochondrialDNA Mutational AnalysisMERRF SyndromeNADH DehydrogenasePedigreeMitochondriaLeigh DiseaseGenes, MitochondrialPolymerase Chain ReactionBase SequenceFrameshift MutationElectron Transport Complex IRNA, Transfer, SerElectron Transport Complex IVMitochondrial Proton-Translocating ATPasesMolecular Sequence DataOxidative PhosphorylationMitochondrial ProteinsGerm-Line MutationSequence Analysis, DNAPenetranceOphthalmoplegia, Chronic Progressive ExternalHeterozygotePhenotypeRNA, Transfer, ArgAging