anticodon and Mitochondrial-Myopathies

A mitochondrial tRNA(Lys) gene mutation at nucleotide position 8344 is responsible for the myoclonus epilepsy associated with ragged-red fibers (MERRF) subgroup of mitochondrial encephalomyopathies. Here, we show that normally modified uridine at the anticodon wobble position remains unmodified in the purified mutant tRNA(Lys). We have reported a similar modification defect at the same position in two mutant mitochondrial tRNAs(Leu)(UUR) in another subgroup, mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS), indicating this defect is common in the two kinds of tRNA molecules with the respective mutations of the two major mitochondrial encephalomyopathies. We therefore suggest the defect in the anticodon is responsible, through the translational process, for the pathogenesis of mitochondrial diseases.

Topics: Anticodon; Cell Line; HeLa Cells; Humans; MELAS Syndrome; MERRF Syndrome; Mitochondria; Mitochondrial Myopathies; Mutation; Point Mutation; RNA, Transfer, Leu; RNA, Transfer, Lys; Uridine

We have identified a novel mitochondrial (mt) DNA mutation in the tRNA(Phe)-gene in a patient with an isolated mitochondrial myopathy. This T to C transition at position 618 disrupts a strictly conserved base pair within the anticodon stem of tRNA(Phe). Computer analysis showed that the affected base pair is essential for anticodon stem formation of tRNA(Phe). The mutant mtDNA was heteroplasmic in skeletal muscle (95% mutant) and peripheral blood cells (20% mutant) from the patient but was undetectable in blood cells from his healthy sister. The patient presented with ragged red fibers and reduced activities of complex I and complex III in skeletal muscle. The T618C mutation described here is the second found in this region. Both mutations affect the same base pair of the tRNA(Phe) anticodon stem substantiating the pathogenic nature of both mutations.

Topics: Adult; Animals; Anticodon; Base Sequence; Cattle; DNA, Mitochondrial; Electron Transport; Humans; Male; Mice; Mitochondrial Myopathies; Molecular Sequence Data; Muscle, Skeletal; Point Mutation; Rats; RNA, Transfer, Phe

Several point mutations in mitochondrial tRNA genes have been linked to distinct clinical subgroups of mitochondrial diseases. A particularly large number of different mutations is found in the tRNA(Leu)(UUR) gene. We show that base substitutions at nucleotide position 3256, 3260, and 3271 of the mitochondrial genome, located in the D and anticodon stem of this tRNA, and mutation 3243 changing a base involved in a tertiary interaction, significantly impair the processing of the tRNA precursor in vitro. In correlation with other studies, our results suggest that inefficient processing of certain mutant variants of mitochondrial tRNA(Leu)(UUR) is a primary molecular impairment leading to mitochondrial dysfunction and consequently to disease.

Topics: Anticodon; Base Sequence; Codon; Endoribonucleases; Genetic Diseases, Inborn; Genetic Variation; Humans; Mitochondrial Myopathies; Molecular Sequence Data; Nucleic Acid Conformation; Point Mutation; Ribonuclease P; RNA; RNA, Catalytic; RNA, Mitochondrial; RNA, Transfer, Leu

We have identified a novel mtDNA mutation in a 29-year-old man with myopathy and diabetes mellitus. This T-->C transition at mtDNA position 14709 alters an evolutionarily conserved nucleotide in the region specifying for the anticodon loop of the mitochondrial tRNA(Glu). The nt-14709 mutation was heteroplasmic but present at very high levels in the patient's muscle, white blood cells (WBCs), and hair follicles; lower proportions of mutated mtDNA were observed in WBCs and hair follicles of all examined maternal relatives. In the patient's muscle, abnormal fibers showed mitochondrial proliferation, severe focal defects in cytochrome c oxidase activity, and absence of cross-reacting material for mitochondrially synthesized polypeptides. These fibers had higher levels of mutated mtDNA than did surrounding "normal" fibers. Although the percentage of mutated mtDNA in WBCs from family members were distributed around the percentage observed in the mothers, the pattern was different in hair follicles, where the mutated population tended to increase in subsequent generations. PCR/RFLP analysis of single hairs showed that the intercellular variations in the percentage of mutated mtDNA differed among family members, with younger generations having a more homogeneous distribution of mutated mtDNA in different hair follicles. These results suggest that the intercellular distribution of the mutated and wild-type mtDNA populations may drift toward homogeneity in subsequent generations.

Topics: Adult; Anticodon; Base Sequence; Diabetes Complications; Diabetes Mellitus; DNA, Mitochondrial; Female; Humans; Male; Meiosis; Mitochondrial Myopathies; Molecular Sequence Data; Muscles; Pedigree; Phenotype; Point Mutation; Protein Biosynthesis; RNA, Transfer, Glu

We have identified an unusual mitochondrial (mt) tRNA mutation in a seven year-old girl with a pure myopathy. This G to A transition at mtDNA position 15990 changed the anticodon normally found in proline tRNAs (UGG) to the one found in serine tRNAs (UGA), and is the first pathogenic anticodon alteration described in a higher eukaryote. The mutant mtDNA was heteroplasmic (85% mutant) in muscle but was undetectable in white blood cells from the patient and her mother. Analysis of single muscle fibres indicated that mutant mtDNAs severely impaired mitochondrial protein synthesis and respiratory chain activity, but only when present at greater than 90%. The recessive behaviour of this mtDNA alteration may explain the patient's relatively mild clinical phenotype.

Topics: Anticodon; Base Sequence; Child; DNA, Mitochondrial; Female; Humans; Mitochondrial Myopathies; Molecular Sequence Data; Muscle Proteins; Muscles; Pedigree; Phenotype; Point Mutation; RNA; RNA, Mitochondrial; RNA, Transfer, Pro; RNA, Transfer, Ser; Tissue Distribution

A patient with a mitochondrial myopathy and biochemically proven profound complex I deficiency has a new mutation in mtDNA. This A-to-G transition at position 3302, involving the aminoacyl stem of tRNA(Leu(UUR)), is associated with abnormal mitochondrial RNA processing. Northern analysis demonstrates marked accumulation of a polycistronic RNA precursor containing sequence for 16 S rRNA, tRNA(Leu(UUR)), and ND1. Comparison of skeletal muscle and skin fibroblasts suggests that the processing error may be quantitatively less severe in this tissue, and biochemical analysis shows that fibroblasts do not express a biochemical defect despite containing the mutation. Important qualitative differences in the processing of this RNA precursor were found when comparing muscle and skin fibroblasts. In muscle, processing appears to occur first at the 5'-end of the tRNA, generating 16 S rRNA plus a tRNA + ND1 intermediate. In fibroblasts, processing occurs at the 3'-end of the tRNA, generating a 16 S rRNA + tRNA intermediate. We suggest that the mutation at position 3302 induces abnormal mitochondrial RNA processing that is linked to the biochemical defect (profound loss of complex I activity), either by qualitative or quantitative abnormalities in the ND1 message. The restriction to skeletal muscle of both the processing error and the biochemical defect suggests that the observed tissue differences in RNA processing play a protective role in skin fibroblasts.

Topics: Adult; Amino Acid Sequence; Animals; Anticodon; Base Sequence; Blotting, Northern; Cells, Cultured; DNA, Mitochondrial; Female; Fibroblasts; Humans; Male; Mitochondrial Myopathies; Molecular Sequence Data; Muscles; NAD(P)H Dehydrogenase (Quinone); Nucleic Acid Conformation; Oligodeoxyribonucleotides; Pedigree; Point Mutation; Polymerase Chain Reaction; Restriction Mapping; RNA Precursors; RNA, Transfer, Leu; Sequence Homology, Nucleic Acid; Skin