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From the Division of Neurology (Drs. Tein and Haslam), the Research Institute (Dr. Tein), and Department of Pathology (Dr. Becker), The Hospital for Sick Children, University of Toronto, Ontario, Canada; the Department of Pediatrics (Dr. Rhead), University of Iowa Hospitals and Clinics, Iowa City, IA; the Departments of Pathology and Pediatrics (Dr. Bennett), University of Texas Southwestern Medical Center at Dallas, TX; and the Department of Medical Genetics (Dr. Vockley), Mayo Clinic and Mayo Foundation, Rochester, MN.
Address correspondence and reprint requests to Dr. Ingrid Tein, Division of Neurology, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G 1X8.
OBJECTIVE: To determine an underlying genetic defect within the differential diagnosis of congenital multicore myopathy.
BACKGROUND: A 13.5-year-old girl presented with congenital-onset facial and neck weakness, slowly progressive severe limb girdle and axial myopathy, respiratory weakness, cardiomyopathy, progressive joint contractures, lumbar lordosis, progressive external ophthalmoplegia with ptosis, and cataracts. Muscle biopsy at 3 years revealed type I fiber predominance and hypotrophy, multicores with a focal decrease in mitochondria and oxidative enzymes, and internal nuclei.
METHODS AND RESULTS: Serum carnitine was decreased (total, 18.2 µmol/L; free, 11.7 µmol/L). Urine organic acids intermittently revealed very large amounts of ethylmalonic and methylsuccinic acids intermittently, with elevated butyrylglycine, 2-methylbutyrylglycine, and tiglylglycine. Fibroblast acylcarnitine profiles revealed marked butyrylcarnitine elevation. Electron-transferring flavoprotein-linked reduction enzymatic assay of fibroblasts with butyrylcoenzyme A (CoA) as substrate, after immunoinactivation of medium-chain acylCoA dehydrogenase activity, revealed a complete absence of short-chain acylCoA dehydrogenase (SCAD) activity. No SCAD protein was detectable with Western blot analysis.
CONCLUSIONS: This patient expands the clinical phenotype of SCAD deficiency and emphasizes the need for its consideration in the differential diagnosis of progressive external ophthalmoplegia and congenital multicore myopathy.
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