Journal Article

A Novel Heteroplasmic tRNA<sup>leu(CUN)</sup> mtDNA Point Mutation in a Sporadic Patient With Mitochondrial Encephalomyopathy Segregates Rapidly in Skeletal Muscle and Suggests an Approach to Therapy

Katherine Fu, Rebecca Hartlen, Timothy Johns, Angela Genge, George Karpati and Eric A. Shoubridge

in Human Molecular Genetics

Volume 5, issue 11, pages 1835-1840
Published in print November 1996 | ISSN: 0964-6906
e-ISSN: 1460-2083 | DOI: http://dx.doi.org/10.1093/hmg/5.11.1835
A Novel Heteroplasmic tRNAleu(CUN) mtDNA Point Mutation in a Sporadic Patient With Mitochondrial Encephalomyopathy Segregates Rapidly in Skeletal Muscle and Suggests an Approach to Therapy

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A novel mtDNA point mutation was detected in the tRNAleu(CUN) gene (G to A at position 12315) in a sporadic patient with chronic progressive external ophthalmoplegia, ptosis, limb weakness, sensorineural hearing loss and a pigmentary retinopathy. The mutation disrupts base pairing in the TΨC stem at a site which has been conserved throughout evolution. Although the other mtDNA tRNAleu gene (UUR) is a hotspot for mutation, this is the first pathogenic mutation to be reported in the gene coding for tRNAleu(CUN). MtDNAs carrying the mutation constituted 94% of total mtDNAs in two separate muscle biopsies. Single fibre analysis showed that skeletal muscle fibres without detectable cytochrome c oxidase activity (COX-ve fibres) contained predominantly mutant mtDNAs (93–98%) while fibres with apparently normal COX activity had up to 90% mutant mtDNAs, demonstrating that the G12315A mutation is functionally recessive. Immunofluorescence studies with specific antibodies to mtDNA- or nuclear-encoded subunits of COX were consistent with a defect in mitochondrial protein translation. The mutation was not present in blood cells or cultured fibroblasts and surprisingly, it could not be detected in satellite cells cultured from the patient's muscle. This pattern, which may be typical of patients who have inherited new germline pathogenic mtDNA mutations, possibly reflects loss of the mutation by random genetic drift in mitotic tissues and proliferation of mitochondria containing the mutant mtDNA in post-mitotic cells. The absence of mtDNA carrying the mutation in satellite cells suggests that regeneration of skeletal muscle fibres from satellite cells could restore a wild-type mtDNA genotype and normal muscle function.

Journal Article.  4713 words.  Illustrated.

Subjects: Genetics and Genomics

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