Congenital dyserythropoietic anaemia type II, or
HEMPAS (hereditary erythroblastic multinuclearity with positive acidified serum lysis test) is a
genetic disease caused by membrane disorganization of erythroid cells. The primary defect of this disease lies in the gene encoding
enzyme(s) which is responsible for the biosynthesis of Asn-linked
oligosaccharides chains of
glycoproteins (Fukuda et al, 1990). In order to know whether this gene defect affects the glycosylation in the cells other than the erythroid cells, the
carbohydrate structures of the
transferrin isolated from the sera of
HEMPAS patients were analysed. Fast atom bombardment mass spectrometry analysis showed the presence of high
mannose type and hybrid type
oligosaccharides in the
HEMPAS transferrin which is in contrast to the complex-type
oligosaccharides found in the normal
transferrin. The results strongly suggest that biosynthesis of Asn-linked
oligosaccharide chains in
HEMPAS hepatocytes is disturbed. As a result, the serum
glycoproteins with incompletely processed
carbohydrates are circulating in the plasma in
HEMPAS patients, but they must have been absorbed by the cells in the liver and the reticuloendothelial cells. Upon
intravenous infusion into rats, as much as 30% of the
HEMPAS transferrin was cleared from the plasma circulation. The majority of the
HEMPAS transferrins was taken up by the liver, and
transferrin was distributed both in the hepatocytes and the Kupffer cells. The presence of enormous amounts of aberrantly glycosylated serum
glycoproteins may lead to the
liver cirrhosis and secondary tissue
siderosis seen in
HEMPAS patients.