[Genetic heterogeneity and the diagnosis of hepatic glycogenoses]

Glycogen storage diseases constitute a highly heterogeneous group of disorders, because of the many complex enzyme systems involved in glycogen metabolism, and also because of the diversity of molecular defects connected with gene mutations. To illustrate these features, the authors studied four types of liver glycogen storage diseases, respectively caused by deficiencies of glucose-6-phosphatase, debranching enzyme, phosphorylase and phosphorylase kinase. In each case, the role and functional characteristics of the enzyme system are described, as well as the bioclinical aspects of the deficiency. The only reliable way of diagnosing glycogen storage disease is by assaying the activity of the enzyme concerned. Assay procedure must take account of various factors, especially the progress made in understanding the nature and mechanism of action of enzyme systems, the possible tissular heterogeneity of the deficiency and the functional characteristics of certain enzymes.