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Late-onset muscle weakness in partial phosphofructokinase deficiency

A unique myopathy with vacuoles, abnormal mitochondria, and absence of the common exon 5/intron 5 junction point mutation

Neuromuscular Diseases Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD. (Dr. Sivakumar) (Dr. Dalakas)
Clinical Neurogenetics Unit, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD. (Dr. Vasconcelos) (Dr. Goldfarb)

Address correspondence and reprint requests to Marinos C. Dalakas, The Neuromuscular Diseases Section, National Institutes for Neurological Disorders and Stroke, National Institutes of Health, Building 10 Room 4N 248, 9000 Rockville Pike, Bethesda, MD 20892.

Three patients (ages 51, 59, and 79) from two generations of an Ashkenazi Jewish family had partial (33% activity) phosphofructokinase (PFK) deficiency that presented with fixed muscle weakness after the age of 50 years. MR spectroscopy revealed accumulation of phosphomonoesters during exercise. Muscle biopsy showed a vacuolar myopathy with increased autophagic activity and several ragged-red and cytochrome c oxidase-negative fibers. The older patient, age 79 at biopsy, had several necrotic fibers. Electron microscopy revealed subsarcolemmal and intermyofibrillar glycogen accumulation and proliferation of mitochondria with paracrystalline inclusions, probably related to reduced availability of energy due to impaired glycolysis. The common point mutation of exon 5/intron 5 junction seen in Jewish Ashkenazi patients with PFK deficiency was excluded. We conclude that late-onset fixed muscle weakness occurs in partial PFK deficiency and it may represent the end result of continuing episodes of muscle fiber destruction. Partial enzyme deficiency in two successive generations suggests a unique molecular mechanism.

Note added in proof. Since submission of this article, we have identified with further molecular genetic analysis that the homozygosity was due to a nonsense mutation in exon 6, codon 95 [CGA(Arg) to TGA(stop)1, as responsible for the patients' phenotype. (Vasconcelos 0, Sivakumar K, Dalakas MC, et al. Proc Natl Acad Sci U S A 1995;92:10322–10326.)

Received May 31, 1995. Accepted in final form July 14, 1995.

This article has been cited by other articles:

				M. C. Dalakas, K.-Y. Park, C. Semino-Mora, H. S. Lee, K. Sivakumar, and L. G. Goldfarb Desmin Myopathy, a Skeletal Myopathy with Cardiomyopathy Caused by Mutations in the Desmin Gene N. Engl. J. Med., March 16, 2000; 342(11): 770 - 780. [Abstract] [Full Text] [PDF]