THE CARBOHYDRATE-DEFICIENT GLYCOPROTEIN SYNDROMES - PRE-GOLGI AND GOLGI DISORDERS

The carbohydrate-deficient glycoprotein syndromes are a recently delin eated group of genetic, multisystemic diseases with major nervous syst em involvement. Three distinct variants have been recognized and there are probably many more. They are characterized by a deficiency of the carbohydrate moiety of secretory glycoproteins, lysosomal enzymes and probably also membranous glycoproteins. The biochemical changes are m ost readily observed in serum transferrin and the diagnosis is usually made by isoelectric focusing of this glycoprotein. The deficiency of sialic acid, in particular, results in a cathodal shift and hence the presence of abnormal isoforms of transferrin with higher isoelectric p oints than normal. The basic defects are probably in the processing an d synthesis of the carbohydrate moiety of glycoproteins; there is indi rect evidence for a deficiency of asparagine-N-linked oligosaccharide transfer in type I (endoplasmic reticulum defect) and for a deficiency of N-acetylglucosaminyltransferase II in type II (Golgi defect). From the large number of patients detected in only a few years, it is expe cted that these diseases will become as important as, for example, the lysosomal, peroxisomal or mitochondrial disorders. Their study will u ndoubtedly yield a wealth of new information on the function of glycop roteins and of their carbohydrate moiety.