Leukocyte Debranching Enzyme in Glycogen Storage

In recent years the classification of glycogen storage disease has been based on the demonstration of a specific enzyme defect for each type (14). Type I, glycogenosis or von Gierke's disease, results from the lack of glucose 6-phosphatase (1). Type II, or Pompe's disease, is characterized clinically by the severity of the disease with cardiovascular complications causing death usually before the eighth month of life (5). Recently Hers has reported that a deficiency of a specific a-glucosidase exists in this condition (3). Type III, or limit dextrinosis, results from a lack of hepatic debranching enzyme or amylo-1-6-glucosidase (6). Type IV is presumed to be due to lack of branching enzyme, although no definite enzymatic assays have been performed to prove this (7). In some classifications, Type V is divided into two subgroups-those with lack of muscle phosphorylase (Vb) (8, 9), and those with a deficiency in hepatic phosphorylase (Va) (10). Others have preferred categorizing patients with muscle phosphorylase deficiency as Type V and those patients with hepatic phosphorylase deficiency as Type VI (4). In many of these types the specific diagnosis can only be made by demonstration of the enzymatic defect in tissue obtained by liver biopsy. In view of the demonstration of low leukocyte phosphorylase in hepatic phosphorylase-deficient glycogen storage disease by Williams and Field ( 11 ) and because of the desirability of using leukocytes rather than liver tissue in establishing the specific enzymatic defect in glycogen storage disease, a method of assay for debranching enzyme has been applied to leukocytes. The results of this assay using leukocytes from patients with glycogen storage disease, their relatives, and a group of control subjects forms the basis of this report. MATERIALS AND METHODS