Abstract
Evidence is presented for defective pyruvate dehydrogenase (EC 4.1.1.1) in leukocytes and muscle tissue from a 10-year old child with persistent lactic acidosis, suffering from myasthenia and growth retardation. The defect is expressed in vitro by a depressed stimulation of pyruvate dehydrogenase catalytic activity by exogenous phosphoprotein phosphatase, and in vivo by a lack of response to muscle work, in comparison with healthy controls. Pyruvate dehydrogenase activity is in the normal range when measured without addition of phosphoprotein phosphatase in cells obtained from the resting patient. The defect reported here represents a new, hitherto undescribed form of a pyruvate dehydrogenase deficiency. The insufficient catalytic activity explains the observed accumulation of pyruvate, lactate, oxaloacetate and alanine and the decrease of citrate concentration in the blood of this patient. Electron microscope studies of the muscle tissue show an enhanced number of enlarged mitochondria with bizarre shapes and high densities of cristae.
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