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.