We used fibroblasts from a baby diagnosed for Leigh syndrome (NDUFS4 W15X), from a baby diagnosed for leukodystrophy (NDUFS1 Q522K), from a child with complex I deficit (NDUFS1 R557X/T595A), and from a patient with familiar Parkinsons disease (PINK W437X) in which mutations in the ND5 and ND6 mitochondrial genes of complex I coexist with mutation in the nuclear phosphatase and tensin homolog- (PTEN-) induced serine/threonine putative kinase-1 (PINK-1) gene. Here, MT-ND6 is linked to Leigh syndrome.