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Exercise intolerance resulting from a muscle-restricted mutation in the mitochondrial tRNA(Leu (CUN)) gene
C Vives-Bauza1, J Gamez, M Roig
1Research Centre for Biochemistry and Molecular Biology, Universitary Hospital Vall d'Hebron, Barcelona, Spain.
Background:
Some patients presenting with isolated lifelong exercise intolerance and ragged-red fibres, harbour skeletal-muscle restricted mutations in their mitochondrial DNA.
Aim:
To identify the molecular defect in a patient presenting with lifelong exercise intolerance, ragged-red fibres and deficiencies of complexes III and IV in skeletal muscle.
Methods:
The muscle biopsy was studied for activities of the respiratory chain, histochemical stains, and sequencing the tRNA genes of mitochondrial DNA.
Results:
The patient had a heteroplasmic mutation in the tRNA(Leu (CUN)) gene of mitochondrial DNA (G12334A). Clinical and morphological data as well as restriction fragment length polymorphism (RFLP) and single-fibre polymerase chain reaction (PCR) analyses strongly indicate that this molecular defect is the primary cause of the myopathy.
Conclusion:
Mutations in any mitochondrial gene should be considered in the differential diagnosis of patients with lifelong exercise intolerance, even when the neurological examination is normal.