Cell membrane anomaly impeding cell division

Clinical aspects and pathogenesis of congenital dyserythropoietic anemias: from morphology to molecular approach

Congenital dyserythropoietic anemias belong to a group of inherited conditions characterized by a maturation arrest during erythropoiesis with a reduced reticulocyte production in contrast with erythroid hyperplasia in bone marrow. The latter shows specific morphological abnormalities that allowed for a morphological classification of these conditions mainly represented by congenital dyserythropoietic anemias types I and II. The identification of their causative genes provided evidence that these conditions have different molecular mechanisms that induce abnormal cell maturation and division. Some altered proteins seem to be involved in the chromatin assembly, such as codanin-1 in congenital dyserythropoietic anemia I. The gene involved in congenital dyserythropoietic anemia II, the most frequent form, is SEC23B. This condition seems to belong to a group of diseases attributable to defects in the transport of newly synthesized proteins from endoplasmic reticulum to the Golgi. This review will analyze recent insights in congenital dyserythropoietic anemias types I and II. It will also attempt to clarify the relationship between mutations in causative genes and the clinical phenotype of these conditions.

The congenital dyserythropoietic anemias

The congenital dyserythropoietic anemias (CDAs) are a heterogeneous group of hereditary disorders that seem to be restricted to the erythroid lineage. They are characterized by morphologic abnormalities of erythroid precursors in the bone marrow, resulting in ineffective erythropoiesis and a suboptimal reticulocyte response. As with many rare disorders, cases of CDA are often misdiagnosed, which may lead to inappropriate management. In this review, the authors highlight the relevant clinical data together with recent molecular advances that should aid decision making in diagnosis and patient management.

Advances in the understanding of the congenital dyserythropoietic anaemias

The congenital dyserythropoietic anaemias (CDAs) are a heterogeneous group of diseases in which the anaemia is predominantly caused by dyserythropoiesis and marked ineffective erythropoiesis; three major (types I, II and III) and several minor subgroups have been identified. Additional information on the natural history of these conditions, the beneficial role of splenectomy in CDA type II and efficacy of interferon-alpha in type I have recently been reported. A disease gene has been localised to a chromosomal segment in the three major types and in CDA type I, a disease gene has been identified (CDANI). Mutations have been detected in both familial and sporadic cases but the predicted protein structure gives few clues as to its function. In both type I and II, there are cases unlinked to the identified localisations, suggesting genetic heterogeneity.

Congenital dyserythropoietic anaemias: clinical features, haematological morphology and new biochemical data

Three types of congenital dyserythropoietic anaemia (CDA) were originally identified on the basis of the pattern of dysplastic changes in the erythroblasts and the results of the acidified serum lysis test (Ham test). These were designated CDA types I, II and III. Several other types have been described subsequently and new forms continue to be reported. Some patients with CDA develop iron overload even without repeated blood transfusion and may present with the complications of severe iron overload. Dysmorphic features are seen in some cases, especially of CDA type I. In CDA type II, incomplete processing of N-linked oligosaccharides leads to a marked reduction of polylactosamines associated with band 3 of the red cell membrane. A few cases of CDA type III develop lymphoid neoplasms. Some of the Swedish cases of CDA type III have developed a retinal abnormality characterized by angioid streaks and macular degeneration. The chromosomal localizations of the disease gene in CDA types I and II and in the Swedish family with CDA type III are now known, but the identities of the mutant genes are still unknown. Cases of CDA type I have shown a partial haematological response to interferon-alpha, however the biochemical basis of this response is unclear. An important step in the diagnosis of sporadic cases of CDA is the exclusion of known causes of acquired dyserythropoiesis.

Red cell membrane protein anomalies in congenital dyserythropoietic anaemia, type II (HEMP AS)

In all of six cases of congenital dyserythropoietic anaemia, type II (HEMPAS), gel electrophoresis in the presence of SDS revealed abnormally rapid migration of the preponderant integral membrane protein, band 3. After proteolysis of intact cells, the remaining part of the band 3, comprising the intramembrane segment and the cytoplasmic domain, migrated electrophoretically as a single band, identical in mobility to that from normal cells treated in the same manner. The anomaly thus resides in the extracellular domain of the protein, which is the glycosylated part of the chain. Peptide digests of the band 3 showed no evidence of a missing protein segment in the abnormal cells and the amino acid composition of the peptides derived from proteolysis of the extracellular protein of intact cells was also normal. We infer that the anomaly is one of glycosylation. The major glycoproteins, detected by carbohydrate-specific (PAS) stain appear normal in SDS gels. However, when the more sensitive procedure of reacting after electrophoresis with radioiodinated lentil lectin is employed, some additional minor protein components are revealed. In particular one species of apparent subunit molecular weight about 150 000 appeared in all cases of HEMPAS examined and in no normals. This component is not accessible to proteolysis by chymotrypsin or Streptomyces griseus protease, and may be associated with the inner membrane patches, characteristic of the HEMPAS condition. Overall cell shape and microviscosity of the membrane bilayer, as measured by fluorescence polarization of a lipid-soluble fluorophore, were substantially normal in HEMPAS cells.

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

Bone marrow CFU-E and BFU-E from a patient with CDA-II formed erythroid colonies and bursts which contained multinucleated erythroblasts in vitro. Adherent cell depletion of the patient's marrow increased CFU-E derived colonies six-fold (98 +/- 17 v. 640 +/- 15 per 10(5) marrow cells plated) and co-culture of CDA-II marrow adherent cells with CSA-II adherent cell depleted marrow significantly suppressed erythroid colony formation. Similar adherent cell suppression of the patient's BFU-E also occurred. Adherent cell depletion of normal marrow did not increase CFU-E derived colony formation (488 +/- 63 v. 495 +/- 108) and decreased BFU-E derived burst formation. Addition of normal adherent cells to normal marrow increased erythroid colony and burst formation. Karyotype and chromosomal banding studies of the patient's multinucleated cells did not show chromosomal inversions, deletions or translocations.

Congenital dyserythropoietic anaemia type II (HEMPAS): a family study

A family having two affected siblings with congenital dyserythropoietic anaemia type II (HEMPAS) is described. The proband was diagnosed after referral for investigation of haemolytic anaemia. Clinical evaluation and in vivo red cell (RBC) survival and the sequestration studies in the proband indicated that the anaemia was due to a combination of ineffective erythropoiesis and premature destruction of RBCs in the spleen. Scanning electron microscopic examination of peripheral RBCs was undertaken and is reported. The polypeptide composition of RBC membranes was also examined using polyacrylamide gel electrophoresis after solubilisation in sodium dodecyl sulphate. These results are also reported.

Morphological Abnormalities in cultured erythroid colonies (BFU-E) from the blood of two patients with HEMPAS

The results of cytological and ultrastructural analysis of erythroid burst colonies derived from the peripheral blood of two patients with HEMPAS have been compared to those obtained in normal controls. Using the plasma clot technique, in studies on 10 subjects we confirmed that most of the colonies consisted or erythroblasts with a synchronous and normal maturation involving a wave of nuclear extrusion at day 13. In contrast, the majority of well-haemoglobinized colonies from HEMPAS consisted of numerous bi- or multinucleated erythroblasts displaying the supplementary double membrane beneath their plasma membrane. This excessive membrane may be present as a continuous or fragmented structure in different erythroblasts from the same colony. These findings suggest that the progeny derived from one BFU-E may vary considerably in their morphological defects. Furthermore, one third of the packed colonies appeared to be formed by non-haemoglobinized cells which were clearly identified by electron microscopy as very early erythroblasts. These cells were unable to mature and subsequently lysed. Thus dyserythropoiesis occurred in culture both at early and late stages of maturation. These studies clearly demonstrate that HEMPAS is a disorder resulting from defective erythroid committed cells.

Electron microscope autoradiographic studies of the erythroblasts of a case of congenital dyserythropoietic anaemia, type II

The bone marrow cells of a patient with congenital dyserythropoietic anaemia, type II, were incubated with 3H-thymidine, 3H-uridine or 3H-leucine for 1 h and studied using the technique of electron microscope autoradiography. Several of the erythroblasts which either displayed the characteristic subsurface double membranes or showed various non-specific abnormalities of the nuclear membrane were found to be actively engaged in DNA, RNA and protein synthesis. Both members of some pairs of erythroblasts which were joined together by a spindle bridge were found to be engaged in DNA synthesis, indicating that some spindle bridges persist for a period longer than the duration of the G1 phase. A small proportion of mononucleate and binucleate late (non-dividing) erythroblasts showed a marked depression or arrest of protein synthesis and some or all of such cells were presumably destined to be phagocytosed by the bone marrow macrophages.

Congenital dyserythropoietic anaemia, types I and II: aberrant pattern of erythrocyte membrane proteins in CDA II, as revealed by two-dimensional polyacrylamide gel electrophoresis

The protein composition of the erythrocyte membrane of two patients with CDA I and four patients with CDA II has been investigated by two-dimensional polyacrylamide gel electrophoresis. The two-dimensional patterns of erythrocyte membrane proteins of the patients with CDA were compared with the well-established pattern of normal individuals. No alterations could be detected in the patients with CDA I, but a striking deviation from normal was observed in all patients with CDA II. The major aberrations of the erythrocyte membrane proteins in CDA II are the lack of protein B1.1, the drastically increased concentration of protein B1.4 and the presence of a new component, C2'. These results are discussed in relation to the known morphological and immunological abnormalities of the erythrocyte membrane in CDA II.

Dyserythropoiesis and annulate lamellae

Cytoplasmic and intranuclear annulate lamellae in the erythroblasts from patients with dyserythropoietic anaemia (megaloblastic anaemia, dysplastic anaemia and erythroleukaemia) are described. Annulate lamellae have mainly been observed in oocytes, in embryonic tissues and in malignant cells. Their occurrence in dyserythropoietic anaemia may be related to the reappearance of fetal characteristics in the erythroblasts and erythrocytes.