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J Neurol Sci. 2010 May 15;292(1-2):107-10. doi: 10.1016/j.jns.2010.01.026. Epub 2010 Feb 18.

The m.12316G>A mutation in the mitochondrial tRNA Leu(CUN) gene is associated with mitochondrial myopathy and respiratory impairment.

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Dino Ferrari Centre, Department of Neurological Sciences, University of Milan, IRCCS Foundation Ospedale Maggiore Policlinico, Mangiagalli and Regina Elena, Milan, Italy.


Mitochondrial disorders are often associated with mutations in mitochondrial tRNA. Independent observation of the same molecular defect in unrelated subjects is a generally required proof of pathogenicity. A sporadic case of chronic external ophthalmoplegia (cPEO) with ragged red fibres (RRFs) has been previously related to an m.12316G>A substitution in tRNA(Leu(CUN)). Sequencing muscle-derived mtDNA, we found the m.12316G>A substitution in an adult woman with mitochondrial myopathy and respiratory impairment. Her muscle biopsy presented several cytochrome c oxidase-negative (COX-) fibres, and RRFs as signs of mitochondrial proliferation. Restriction-fragment length polymorphism (RFLP) analysis of the mutation in isolated muscle fibres showed a threshold of at least 60% of mutated mtDNA to determine a COX deficiency phenotype. This second report of the m.12316G>A mutation in a sporadic patient consolidates its pathogenic nature and provides further elements for genetic counselling.

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