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Friedreich ataxia

III. Mitochondrial malic enzyme deficiency

Departments of Neurology and Pediatrics, School of Medicine, The University of Colorado Health Sciences Center, Denver, CO.

Polarographic assays of oxidative phosphorylation in muscle mitochondria indicated abnormal pyruvate-malate metabolism in Friedreich ataxia (FA). Pursuing this clue, more specific assays were performed. Mitochondrial malic enzyme (ME_m; malate: NADP oxidoreductase) specific activity was 10% of controls in fibroblasts from eight FA patients (p < 0.0001). Cytosolic malic enzyme was modestly increased in FA fibroblasts. Mitochondrial and cytosolic malate dehydrogenase and aspartate aminotransferase, and malate transport on the dicarboxylate and a-ketoglutarate carriers were normal in fibroblasts or leukocytes.

ME_m activity is normally highest in the nervous system and heart and is important in regulating carbohydrate metabolism. ME_m deficiency could cause FA; further studies are required to substantiate this hypothesis.

Address correspondence and reprint requests to Dr. Stumpf, Director of Pediatric Neurology, University of Colorado Health Sciences Center, Box C229, 4200 East Ninth Avenue, Denver, CO 80262.

This work was supported by a Clinical Research Grant from the Muscular Dystrophy Association; NIH Program Project Grant HD08315, Center Grant HD04024 and National Research Service Award Grant HD07096–01, all from NICHD; Pediatric and Adult CRC Grant RR00069 from the General Clinical Research Centers Program of the Division of Research Resources, and funding from the Friedreich's Ataxia Group in America, Inc.

Accepted for publication September 2, 1981.

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