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Marcus Deschauer, MD; Helen Swalwell, BSc; Maria Strauss, MD; Stephan Zierz, MD; Robert W. Taylor, PhD, MRCPath

Arch Neurol. 2006;63:902-905.

Background  An extensive range of molecular defects have been identified in the human mitochondrial genome (mitochondrial DNA); many are associated with well-characterized, progressive neurological syndromes, but a minority of patients have uncharacteristic phenotypes in which symptoms may be relatively mild.

Objective  To describe a novel transfer RNA^Phe mutation of mitochondrial DNA in a late-onset case with a mild phenotype of mitochondrial disease.

Design  Case report.

Patient  A 66-year-old woman presented with a 4-year history of walking difficulties due to exercise intolerance and paresthesia in the feet. Clinical examination results were normal. Her deceased mother had similar walking difficulties, but her sister and 2 children were unaffected.

Results  The demonstration of a marked histochemical defect in cytochrome c oxidase activity on muscle biopsy prompted molecular investigation of mitochondrial DNA, revealing a novel maternally inherited mutation in the variable loop of the mitochondrial transfer RNA^Phe gene. This 622G>A transition was heteroplasmic and segregated with cytochrome c oxidase deficiency in single fibers.

Conclusion  This case serves to illustrate that primary defects of the mitochondrial genome should be considered even in older patients with late-onset, mild neuromuscular symptoms.

Author Affiliations: Department of Neurology, Martin-Luther-Universität Halle-Wittenberg, Halle/Saale, Germany (Drs Deschauer, Strauss, and Zierz); Mitochondrial Research Group, School of Neurology, Neurobiology and Psychiatry, The Medical School, University of Newcastle upon Tyne, Newcastle upon Tyne, United Kingdom (Ms Swalwell and Dr Taylor).

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