Defect in glycosylation of erythrocyte membrane proteins in congenital dyserythropoietic anaemia type II (HEMPAS).

Congenital dyserythropoietic anaemia type II (HEMPAS) is a hereditary disease believed to be caused by a membrane abnormality of erythroid cells. Since the molecular basis of this membrane abnormality has not yet been defined, membrane glycoproteins of HEMPAS erythrocytes were analysed by cell surface labelling and endo-beta-galactosidase digestion in this study. HEMPAS erythrocytes showed an abnormal glycoprotein profile when cells were labelled by the galactose oxidase/NaB[3H]4 method; Band 3 and Band 4.5 glycoproteins in HEMPAS are labelled but with less intensity although normally these proteins are the major components revealed by the same method. Instead, in HEMPAS, labelled lactosaminoglycans were found as a lower molecular weight glycoconjugate (HEMPAS glycan). HEMPAS glycan was characterized by micelle formation, a monomer molecular weight of 4000, susceptibility to endo-beta-galactosidase and resistance to protease. These characteristics suggest that HEMPAS glycan has the nature of macroglycolipid. Proteins of Band 3 and the glucose transport protein (a component of Band 4.5), which were detected by antibodies showed a slightly decreased molecular weight in HEMPAS erythrocytes compared to those from normal erythrocytes, which was consistent with the decreased glycosylation of these proteins. The results indicate that anomalies in glycosylation occurred specifically in lactosaminoglycan glycoproteins of HEMPAS erythrocytes.