GENETIC DEFICIENCIES OF THE GLYCOGEN-PHOSPHORYLASE SYSTEM

Several types of glycogen storage disease attributable to a deficiency of phosphorylase or phosphorylase kinase have been described. These d iseases have been divided according to clinical symptoms, mode of inhe ritance, and affected tissue. However, this classification is question able, as the clinical symptoms of these different diseases are similar , the mode of inheritance is often difficult to establish, and the bio chemical assays are subject to several technical problems. A better cl assification would be based upon the identification of mutations in th e respective disease genes. The molecular heterogeneity, however, is l arge, and at least 10 genes are involved. Mutations have been found in the muscle phosphorylase gene in patients with muscle phosphorylase d eficiency, in the gene encoding the liver a subunit of phosphorylase k inase in patients with X-linked liver glycogenosis, and in the gene fo r the muscle a subunit of phosphorylase kinase in a patient with muscl e phosphorylase kinase deficiency. We review here the different defici encies of the phosphorylase system.