Composition of the intra-erythroblastic precipitates in thalassaemia and congenital dyserythropoietic anaemia (CDA): identification of a new type of CDA with intra-erythroblastic precipitates not reacting with monoclonal antibodies to - and -globin chains S. N. WICKRAMASINGHE , M. J. L EE , T. F URUKAWA,* M. E GUCHI * AND C. D. L. R EID † Department of Haematology, Imperial College School of Medicine at St Mary’s, London, U.K., *Second Department of Paediatrics, Dokkyo University School of Medicine,Mibu-machi, Japan, and †Department of Haematology, Northwick Park Hospital, Harrow, Middlesex, U.K. Received 4 September 1995; accepted for publication 12 February 1996 Summary. Ultrathin sections of bone marrow cells from two patients with homozygous -thalassaemia, two patients with haemoglobin H (HbH) disease, a patient with congenital dyserythropoietic anaemia (CDA) type III and two patients with severe congenital dyserythropoietic anaemia of an unusual type were reacted with mouse monoclonal antibodies against various globin chains and the reactionvisualized using a gold-labelled goat antibodyagainst mouse IgG. The multiple rounded intra-erythroblastic inclusions found in homozygous -thalassaemiareacted with the monoclonal antibody against -globin chains but not -globin chains, thus confirming that they consisted of precipitated -globin chains. The branching intra-erythroblastic inclusions found in HbH disease and CDA type III reacted with the monoclonal antibody against - globin chains but not -globin chains, indicating that they consisted of precipitated -globin chains. The two patients with severe CDA had been transfusion-dependent since infancy, had a normal : globin chain synthesis ratio or parents with normal red cell indices, displayed prominent dysplastic changes in their erythroblasts, and had intra- erythroblastic inclusions resembling those seen in homozy- gous -thalassaemia. However, unlike those in -thalassae- mia, the inclusions in these two patients did not react with the monoclonal antibody against either - or -globin chains. The inclusions reacted with antibody against -globin chains, but detailed studies in one of the patients indicated that the antigen involved was not -globin. These patients have features not reported in the condition known as dominantly inherited inclusion body -thalassaemia and appear to suffer from a novel type of CDA in which the intra-erythroblastic inclusions may consist of some non-globin protein or structurally-abnormal -globin chains. Keywords: congenital dyserythropoietic anaemia, thalas- saemia, intra-erythroblastic inclusions, immunoelectron- microscopy. Supravitally-stained erythroblasts from patients with homo- zygous -thalassaemia contain inclusions that are visible under the light microscope (Fessas, 1963; Yataganas & Fessas, 1969; Wickramasinghe et al, 1973). Analysis of these inclusions by peptide fingerprinting has indicated that they consist largely, if not exclusively, of precipitated -globin chains (Fessas et al, 1966). Under the electron microscope, such precipitates appear as multiple rounded foci of amorphous electron-dense material which tend to become confluent (Polliack & Rachmilewitz, 1973; Wickramasinghe & Bush, 1975). Ultrastructurally different electron-dense intra-erythroblastic inclusions have been reported in HbH disease and -thalassaemia trait (Wickramasinghe et al, 1980, 1984). These are elongated, branching or stellate, and have distinct edges. Although there are no data on their chemical composition, such inclusions have been assumed to consist of precipitated -globin chains. Inclusions similar to those found in HbH disease have also been reported in British Journal of Haematology , 1996, 93, 576–585 576 1996 Blackwell Science Ltd Correspondence: Professor S. N. Wickramasinghe, Department of Haematology, Imperial College School of Medicine at St Mary’s, Norfolk Place, London W2 1PG.