A Case of Mcardle's Syndrome with a Positive Family History.

McArdle (1951) described the case of a man who from early childhood was unable to maintain exercise, because muscle pain and stiffness developed during it. He found that blood concentrations of lactate and pyruvate did not increase in the usual way after exercise in this patient and therefore deduced that there was a defective breakdown of muscle glycogen. Other patients with similar symptoms and biochemical abnormalities have been described and their skeletal muscle shown to lack phosphorylase (Mommaerts, Illingworth, Pearson, Guillory and Seraydarian, 1959; Schmid and Mahler, 1959; Pearson, Rimer and Mommaerts, 1961; Thomson, MacLaurin and Prineas, 1963; Rowland, Fahn, and Schotland, 1963). The excess glycogen observed in skeletal muscle in these cases is explicable by a method of glycogen synthesis via uridine nucleotides that does not involve phosphorylase (Leloir and Cardini, 1957). The onset early in life and the associated enzymatic defect suggest a genetic abnormality in McArdle's syndrome, while its rarity and the involvement of only one enzyme implicate a single gene. However, only one detailed report of an affected family (Schmid and Hammaker, 1961) supported this hypothesis until two recent descriptions. Engel, Eyerman, and Williams (1963) reported a defect of phosphorylase in siblings whose symptoms appeared only late in life, while Rowland et al. (1963) described a patient with a typical history of muscle pain and myoglobinuria who had one first cousin who complained of muscular arching and dark urine occasionally. Although the parents of their patient were themselves first cousins, none of his four sibs were affected. Also, Mahler stated (Schmid and Mahler, 1959) that among six patients whom he had seen with the clinical and biochemical findings of McArdle's syndrome there were two sisters in whom muscle studies had not been possible.