IN 1951, McArdle1 described a 30-year-old man who suffered from severe muscle cramps and weakness following exertion. The symptoms were relieved by rest, and results of neurological examination were entirely normal. A disorder of glycogen breakdown was presumed on the basis of the failure of the patient's blood lactate level to rise following exercise under ischemicconditions. It was shown in subsequent similar cases2-5 that there was an absence of muscle phosphorylase, the initial enzyme of glycolysis reacting directly with branched glycogen. Findings from muscle biopsies2-5 demonstrated abnormal aggregates of glycogen within the muscle, both in the form of subsarcolemmal "blebs" and in more central regions of the fibers. These findings were confirmed by electronmicroscopy.6,7 Subsequently, other examples of myopathy associated with different abnormalities of glycogen metabolism have been presented. These have included the absence of the enzymes α-glucosidase (amylo-1,4-glucosidase),8-11 amylo-1,6-glucosidase (debrancher),12-14 phosphohexoisomerase,15
Slotwiner P, Song SK, Maker HS. Myopathy Resembling McArdle's Syndrome. Arch Neurol. 1969;20(6):586–598. doi:10.1001/archneur.1969.00480120032002
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