Laboratory diagnosis of glycogen diseases

Erythrocyte galactokinase assay with high performance liquid chromatography

An assay for erythtocyte galactokinase based on high performance liquid chromatographic determination of galactose 1-phosphate (Gal-1-P) is described. The determination of Gal-1-P was applied to a post-column fluorometric detection of reducing sugars using arginine. This method is as sensitive and accurate as conventional radioisotopic methods, but needs no radioisotopic facilities. It requires only a small blood sample and is suitable as a follow-up test in neonatal screening.

Enzymatic activity of glycogen metabolism in chorionic villi

Glycogen content and six major enzymatic activities involved in glycogen metabolism were analysed in chorionic villi (CV). Glycogen levels were found to be lower than those known to exist in liver and muscle. Activities of alpha-glucosidase, amylo-1,6-glucosidase, phosphorylase b and phosphorylase kinase were detectable by standard methods. The enzymatic activities of glucose-6-phosphatase and phosphorylase a were undetectable. These findings suggest that CV biopsies can be useful for first-trimester diagnosis of glycogen storage disease types II, III and VI, but not for type I (glucose-6-phosphatase deficiency).

Glycogenesis and glyconeogenesis in human platelets. Incorporation of glucose, pyruvate, and citrate into platelet glycogen; glycogen synthetase and fructose-1,6-diphosphatase activity

Washed human platelets are capable of depositing 1-4 as well as probable 1-6 glucosyl linkages onto preexistent glycogen primer. They are also capable of degrading (glycogenolysis) newly synthesized 1-4 as well as probable 1-6 glucosyl linkages. A higher rate of glycogen synthesis was found in platelet suspensions containing lower concentrations of platelets. This was shown to result from decreased glycogen degradation and consequent increased residual glycogen primer in low platelet suspensions. The increased glycogen content of low platelet suspensions was not a result of platelet washing, removal of platelets from plasma, or release of platelet metabolites into the media. The enzyme glycogen synthetase was found to be present at a rate of 5.2 mumoles of uridine diphosphate (UDP) glucose incorporated into glycogen per gram platelets per hour at 37 degrees C. The K(m) for UDP glucose was 6.6 mmoles/liter. At optimum concentration of glucose 6-phosphate, the K(m) was reduced 4.6 fold and V(max) was increased 4.3-fold. Human platelets contain the glyconeogenic pathway. They incorporate pyruvate-(14)C and citrate-(14)C into platelet glycogen and contain an apparent fructose-1,6-diphosphatase. The apparent fructose-1,6-diphosphatase was activated by adenosine monophosphate (AMP) and adenosine diphosphate (ADP), inhibited by adenosine triphosphate (ATP), and shown to be rate limiting for glyconeogenesis at physiologic concentration of adenine nucleotide.

Glucose and glycogen metabolism in erythrocytes from normal and glycogen storage disease type III subjects

Active glycogen metabolism has been demonstrated in both normal and glycogen-rich erythrocytes taken from patients with type III glycogen storage disease. Activity of all enzymes catalyzing the reactions required for the synthesis and degradation of glycogen have been demonstrated in the mature erythrocytes. Uniformly labeled glucose-(14)C is incorporated into glycogen in intact cells of both types during incubation. Replacement of the glucose-(14)C by unlabeled glucose in the medium resulted in a significant loss of radioactivity from cellular glycogen. In the absence of the substrate a progressive shortening of outer branches occurred during incubation of intact glucogen-rich cells. Using cells from patients with type III glycogen storage disease, which have sufficient glycogen content to be analyzed by beta-amylolysis, we demonstrated that the glucosyl units are first incorporated in the outer tiers, then transferred to the core where they tend to accumulate due to the absence of amylo-1,6-glucosidase. The glycogen-rich cells have a more rapid rate of glucose utilization upon incubation which is not reflected by a higher lactate production. The increased rate of glucose utilization did not result from an increased rate of glucose incorporation into glycogen in affected cells. The rate of (14)CO(2) production from glucose-1-(14)C during incubation was not significantly different in the two types of cells unless methylene blue was added as an electron acceptor, in which case the glycogen-rich cells oxidized glucose to CO(2) more rapidly.