Congenital dyserythropoietic anaemia type II (CDA-II): chromosomal banding studies and adherent cell effects on erythroid colony (CFU-E) and burst (BFU-E) formation

Pure red cell aplasia--evidence for an inhibitory action of the bone marrow adherent cell layer

Evidence is presented for an inhibitory action of the bone marrow adherent cell layer on erythropoiesis in a case of pure red cell aplasia. Cultures of the patient's bone marrow with autologous and normal plasma showed normal numbers of CFU-C, but total absence of BFU-E. There was no inhibition of BFU-E when normal bone marrow was cultured with the patient's plasma. T-cell depletion of the patient's bone marrow did not affect these results, but after removal of the adherent cells, normal numbers of BFU-E were cultured. These observations suggest that the adherent cells, which are predominantly macrophages, were responsible for the inhibitory action on erythropoiesis.

Congenital dyserythropoietic anemias

The congenital dyserythropoietic anemias (CDAs) are a group of relatively rare inherited anemias that share in common ineffective erythropoiesis and morphologic abnormalities of mature red blood cells and their precursors. Three major types of CDA and a number of variants have been described. The diagnosis and categorization of these disorders are facilitated by microscopic examination of the blood and bone marrow and by serologic testing. Management of patients currently consists of observation and supportive care. Because patients with CDAs may be at significant risk for secondary hemochromatosis, they require monitoring for this condition. Splenectomy may be of benefit in certain cases in which the anemia is particularly severe. Over the past few years advances have been made in understanding the pathogenesis of these disorders, and it now appears that CDA II results from enzymatic defects in the cellular glycosylation pathway.

Congenital dyserythropoietic anemia type II: morphological characterization of the erythroid colonies (BFU-E) from the bone marrow and peripheral blood of two patients

The numerical and morphological findings of erythroid burst colonies from the peripheral blood and bone marrow of two patients with congenital dyserythropoietic anemia type II (CDA-II) are described. In both patients there was an increase of medullary and peripheral BFU-E that was explained by a compensating mechanism against the destruction of erythrocytes. In most of the colonies normal and abnormal erythroblasts co-existed. The ultrastructural analysis of erythroblasts showed, as in vivo, bi- and multinuclearity, autophagic vacuoles, and aberrant membranes that sometimes gave rise to the double-membrane appearance. These abnormalities were found in both patients simultaneously in the blood and bone marrow. These findings point to defective erythroid stem cells. The clinical expression of the disease may depend partly on the ratio of normal to abnormal erythroid colonies.

Congenital dyserythropoietic anaemia type II (HEMPAS) and its molecular basis

Congenital dyserythropoietic anaemia type II (CDA II) is a rare genetic anaemia in humans, inherited in an autosomally recessive mode. CDA II is also called HEMPAS as this disease is characterized by hereditary erythroblastic multinuclearity with positive acidified serum lysis test. Analyses of CDA II erythrocyte membranes showed that the band 3 glycoprotein is underglycosylated. An aberrant glycosylation pattern is seen in the polylactosamine carbohydrates which are normally attached to the band 3 and band 4.5 glycoproteins. The polylactosamines are, however, accumulated in the form of glycolipids. Therefore a genetic factor in CDA II appears to block the glycosylation of protein acceptors and shift these carbohydrates to the lipid acceptors. Structural analysis of CDA II band 3 carbohydrates identified truncated hybrid-type oligosaccharides and suggests that the Golgi glycosylation enzyme(s), alpha-mannosidase II or N-acetylglycosaminyltransferase II is defective in CDA II. By using a cDNA probe for alpha-mannosidase II, one CDA II case has been identified as being defective in the gene encoding alpha-mannosidase II. At present, it is not clear whether CDA II is a genetically heterogenous collection of glycosylation deficiencies, or genetically homogenous but apparently heterogenous in phenotype expression. Freeze-fracture electron microscopy and immunoelectron microscopy revealed that the band 3 glycoproteins are clustered in CDA II erythrocyte membranes. The abnormal distribution of band 3 might cause an unstable membrane organization. In CDA II erythroblasts, the membrane proteins might also be underglycosylated and abnormally distributed. When normal erythroblasts were cultured in vitro in the presence of swainsonine (alpha-mannosidase inhibitor) the erythroblasts became multinucleared. It is, therefore, quite possible that the enzymic defect of alpha-mannosidase II could cause various morphological anomalies including multinuclearity. Because the genes encoding glycosylation enzymes are housekeeping genes, the enzyme defect of CDA II is not restricted to erythroid cells and there is also an abnormal glycosylation of hepatocyte glycoproteins. On the other hand, there are many types of cells and tissues which appear not to be affected by the CDA II defect. A mechanism for the erythroid-specific manifestation of CDA II and its tissue specificity are also discussed.

Effects of dexamethasone on erythroid colony and burst formation from human fetal liver and adult marrow

Dexamethasone, a prototypic synthetic glucocorticoid, was added to cultures of human fetal liver and adult marrow cells to assess its effects on erythroid colony and burst formation. Dexamethasone decreased the number of fetal liver erythroid colonies and bursts formed in the presence of erythropoietin, and also decreased the number of cells per colony. The amount and type of haemoglobin produced per cell were unaffected by adding dexamethasone to the cultures. Dexamethasone inhibited the incorporation of 3H-thymidine into DNA in fetal liver cells stimulated with erythropoietin, supporting the hypothesis that dexamethasone inhibits the proliferation but not the differentiation of fetal liver CFU-E and BFU-E. In contrast, addition of dexamethasone to adult bone marrow cultures had a variable effect on erythroid colony and burst formation.