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

New Cases and Mutations in SEC23B Gene Causing Congenital Dyserythropoietic Anemia Type II

Congenital dyserythropoietic anemia type II (CDA II) is an inherited autosomal recessive blood disorder which belongs to the wide group of ineffective erythropoiesis conditions. It is characterized by mild to severe normocytic anemia, jaundice, and splenomegaly owing to the hemolytic component. This often leads to liver iron overload and gallstones. CDA II is caused by biallelic mutations in the SEC23B gene. In this study, we report 9 new CDA II cases and identify 16 pathogenic variants, 6 of which are novel. The newly reported variants in SEC23B include three missenses (p.Thr445Arg, p.Tyr579Cys, and p.Arg701His), one frameshift (p.Asp693GlyfsTer2), and two splicing variants (c.1512-2A>G, and the complex intronic variant c.1512-3delinsTT linked to c.1512-16_1512-7delACTCTGGAAT in the same allele). Computational analyses of the missense variants indicated a loss of key residue interactions within the beta sheet and the helical and gelsolin domains, respectively. Analysis of SEC23B protein levels done in patient-derived lymphoblastoid cell lines (LCLs) showed a significant decrease in SEC23B protein expression, in the absence of SEC23A compensation. Reduced SEC23B mRNA expression was only detected in two probands carrying nonsense and frameshift variants; the remaining patients showed either higher gene expression levels or no expression changes at all. The skipping of exons 13 and 14 in the newly reported complex variant c.1512-3delinsTT/c.1512-16_1512-7delACTCTGGAAT results in a shorter protein isoform, as assessed by RT-PCR followed by Sanger sequencing. In this work, we summarize a comprehensive spectrum of SEC23B variants, describe nine new CDA II cases accounting for six previously unreported variants, and discuss innovative therapeutic approaches for CDA II.

Consequences of mutations in the genes of the ER export machinery COPII in vertebrates

Coat protein complex II (COPII) plays an essential role in the export of cargo molecules such as secretory proteins, membrane proteins, and lipids from the endoplasmic reticulum (ER). In yeast, the COPII machinery is critical for cell viability as most COPII knockout mutants fail to survive. In mice and fish, homozygous knockout mutants of most COPII genes are embryonic lethal, reflecting the essentiality of the COPII machinery in the early stages of vertebrate development. In humans, COPII mutations, which are often hypomorphic, cause diseases having distinct clinical features. This is interesting as the fundamental cellular defect of these diseases, that is, failure of ER export, is similar. Analyses of humans and animals carrying COPII mutations have revealed clues to why a similar ER export defect can cause such different diseases. Previous reviews have focused mainly on the deficit of secretory or membrane proteins in the final destinations because of an ER export block. In this review, we also underscore the other consequence of the ER export block, namely ER stress triggered by the accumulation of cargo proteins in the ER.

Analysis of a cohort of 101 CDAII patients: description of 24 new molecular variants and genotype-phenotype correlations

Congenital dyserythropoietic anaemia type II (CDAII) is a rare autosomal recessive disease characterized by ineffective erythropoiesis, haemolysis, erythroblast morphological abnormalities, hypoglycosylation of some red blood cell membrane proteins, particularly band 3, and mutations in the SEC23B gene. We report the analysis of 101 patients from 91 families with a median follow-up of 23 years (range 0-65); 68 patients are newly reported. Clinical and haematological parameters were separately analysed in early infancy and thereafter, when feasible. Molecular analysis of the SEC23B gene confirmed the high heterogeneity of the defect, leading to the identification of 54 different mutations, 24 of which are newly described. To evaluate the genotype-phenotype correlation, patients were grouped according to their genotype (two missense mutations vs. one missense/one drastic mutation) and assigned to two different severity gradings based on laboratory data and on therapeutic needs; by this approach only a weak genotype-phenotype correlation was observed in the analysed groups.

Characteristic phenotypes associated with congenital dyserythropoietic anemia (type II) manifest at different stages of erythropoiesis

Congenital dyserythropoietic anemia type II is an autosomally recessive form of hereditary anemia caused by SEC23B gene mutations. Patients exhibit characteristic phenotypes including multinucleate erythroblasts, erythrocytes with hypoglycosylated membrane proteins and an apparent double plasma membrane. Despite ubiquitous expression of SEC23B, the effects of mutations in this gene are confined to the erythroid lineage and the basis of this erythroid specificity remains to be defined. In addition, little is known regarding the stage at which the disparate phenotypes of this disease manifest during erythropoiesis. We employ an in vitro culture system to monitor the appearance of the defining phenotypes associated with congenital dyserythropoietic anemia type II during terminal differentiation of erythroblasts derived from small volumes of patient peripheral blood. Membrane protein hypoglycosylation was detected by the basophilic stage, preceding the onset of multinuclearity in orthochromatic erythroblasts that occurs coincident with the loss of secretory pathway proteins including SEC23A during erythropoiesis. Endoplasmic reticulum remnants were observed in nascent reticulocytes of both diseased and healthy donor cultures but were lost upon further maturation of normal reticulocytes, implicating a defect of ER clearance during reticulocyte maturation in congenital dyserythropoietic anemia type II. We also demonstrate distinct isoform and species-specific expression profiles of SEC23 during terminal erythroid differentiation and identify a prolonged expression of SEC23A in murine erythropoiesis compared to humans. We propose that SEC23A is able to compensate for the absence of SEC23B in mouse erythroblasts, providing a basis for the absence of phenotype within the erythroid lineage of a recently described SEC23B knockout mouse.

Inherited hematological disorders due to defects in coat protein (COP)II complex

Many diseases attributed to trafficking defects are primary disorders of protein folding and assembly. However, an increasing number of disease states are directly attributable to defects in trafficking machinery. In this context, the cytoplasmic coat protein (COP)II complex plays a pivotal role: it mediates the anterograde transport of correctly folded secretory cargo from the endoplasmic reticulum towards the Golgi apparatus. This review attempts to describe the involvement of COPII complex alteration in the pathogenesis of human genetic disorders; particularly, we will focus on two disorders, the Congenital Dyserythropoietic Anemia type II and the Combined Deficiency of Factor V and VIII.

Congenital dyserythropoietic anemia type II: molecular analysis and expression of the SEC23B gene

Background

Congenital dyserythropoietic anemia type II (CDAII), the most common form of CDA, is an autosomal recessive condition. CDAII diagnosis is based on invasive, expensive, and time consuming tests that are available only in specialized laboratories. The recent identification of SEC23B mutations as the cause of CDAII opens new possibilities for the molecular diagnosis of the disease. The aim of this study was to characterize molecular genomic SEC23B defects in 16 unrelated patients affected by CDAII and correlate the identified genetic alterations with SEC23B transcript and protein levels in erythroid precursors.

Methods

SEC23B was sequenced in 16 patients, their relatives and 100 control participants. SEC23B transcript level were studied by quantitative PCR (qPCR) in peripheral erythroid precursors and lymphocytes from the patients and healthy control participants. Sec23B protein content was analyzed by immunoblotting in samples of erythroblast cells from CDAII patients and healthy controls.

Results

All of the investigated cases carried SEC23B mutations on both alleles, with the exception of two patients in which a single heterozygous mutation was found. We identified 15 different SEC23B mutations, of which four represent novel mutations: p.Gln214Stop, p.Thr485Ala, p.Val637Gly, and p.Ser727Phe. The CDAII patients exhibited a 40-60% decrease of SEC23B mRNA levels in erythroid precursors when compared with the corresponding cell type from healthy participants. The largest decrease was observed in compound heterozygote patients with missense/nonsense mutations. In three patients, Sec23B protein levels were evaluated in erythroid precursors and found to be strictly correlated with the reduction observed at the transcript level. We also demonstrate that Sec23B mRNA expression levels in lymphocytes and erythroblasts are similar.

Conclusions

In this study, we identified four novel SEC23B mutations associated with CDAII disease. We also demonstrate that the genetic alteration results in a significant decrease of SEC23B transcript in erythroid precursors. Similar down-regulation was observed in peripheral lymphocytes, suggesting that the use of these cells might be sufficient in the identification of Sec23B gene alterations. Finally, we demonstrate that decreased Sec23B protein levels in erythroid precursors correlate with down-regulation of the SEC23B mRNA transcript.

Two founder mutations in the SEC23B gene account for the relatively high frequency of CDA II in the Italian population

Congenital Dyserythropoietic Anemia type II is an autosomal recessive disorder characterized by unique abnormalities in the differentiation of cells of the erythroid lineage. The vast majority of CDA II cases result from mutations in the SEC23B gene. To date, 53 different causative mutations have been reported in 86 unrelated cases (from the CDA II European Registry), 47 of them Italian. We have now identified SEC23B mutations in 23 additional patients, 17 Italians and 6 non-Italian Europeans. The relative allelic frequency of the mutations was then reassessed in a total of 64 Italian and 45 non-Italian unrelated patients. Two mutations, E109K and R14W, account for over one-half of the cases of CDA II in Italy. Whereas the relative frequency of E109K is similar in Italy and in the rest of Europe (and is also prevalent in Moroccan Jews), the relative frequency of R14W is significantly higher in Italy (26.3% vs. 10.7%). By haplotype analysis we demonstrated that both are founder mutations in the Italian population. By using the DMLE+ program our estimate for the age of the E109K mutation in Italian population is ≈2,200 years; whereas for the R14W mutation it is ≈3,000 years. We hypothesize that E109K may have originated in the Middle East and may have spread in the heyday of the Roman Empire. Instead, R14W may have originated in Southern Italy. The relatively high frequency of the R14W mutation may account for the known increased prevalence of CDA II in Italy. Am. J. Hematol. 86:727–732, 2011. © 2011 Wiley-Liss, Inc.

Epidemiology of rare anaemias in Europe

Registry and epidemiological data of Rare Anaemias (RA) in Europe is in general still incomplete and/or partially documented. One important issue is the increasing prevalence of haemoglobin disorders (HD) due to migrations from high prevalence areas. The size of the problem, particularly for sickle cell disease (SCD), is already having an impact on health services in many European countries. The best known cause of rare anaemias associated with congenital haemolytic anaemia (CHA) in Europe is Hereditary Spherocytosis (HS) a red blood cell (RBC) membrane defect with a prevalence of 1 to 5 cases per 10.000 individuals. Some other causes of CHA are extremely rare and only few individual cases have been described worldwide (i.e. some RBC enzymopathies). Congenital defects of erythropoiesis are less frequent Diamond-Blackfan Anaemia (DBA) and Fanconi Anaemia (FA) exhibit a very low prevalence ranging from 4 to 7 per million live births. Congenital Dyserythropoietic Anaemia (CDA), a genetically heterogenous group, is still less frequent and exhibits a large variability of frequency depending on the European region: 0.1-3.0 cases per million births In addition many cases are known from a large autosomal dominant family in Sweden. Although incidence of Paroxysmal Nocturnal Haemoglobinuria (PNH) in Europe is still unknown, data collection from different sources has given quotes of 1 case per 100,000 individuals to 5 cases per million births.

Mutational spectrum in congenital dyserythropoietic anemia type II: identification of 19 novel variants in SEC23B gene

SEC23B gene encodes an essential component of the coat protein complex II (COPII)-coated vesicles. Mutations in this gene cause the vast majority the congenital dyserythropoietic anemia Type II (CDA II), a rare disorder resulting from impaired erythropoiesis. Here, we investigated 28 CDA II patients from 21 unrelated families enrolled in the CDA II International Registry. Overall, we found 19 novel variants [c.2270 A>C p.H757P; c.2149−2 A>G; c.1109+1 G>A; c.387(delG) p.L129LfsX26; c.1858 A>G p.M620V; c.1832 G>C p.R611P; c.1735 T>A p.Y579N; c.1254 T>G p.I418M; c.1015 C>T p.R339X; c.1603 C>T p.R535X; c.1654 C>T p.L552F; c.1307 C>T p.S436L; c.279+3 A>G; c. 2150(delC) p.A717VfsX7; c.1733 T>C p.L578P; c.1109+5 G>A; c.221+31 A>G; c.367 C>T p.R123X; c.1857_1859delCAT; p.I619del] in the homozygous or the compound heterozygous state. Homozygosity or compound heterozygosity for two nonsense mutations was never found. In four cases the sequencing analysis has failed to find two mutations. To discuss the putative functional consequences of missense mutations, computational analysis and sequence alignment were performed. Our data underscore the high allelic heterogeneity of CDA II, as the most of SEC23B variations are inherited as private mutations. In this mutation update, we also provided a tool to improve and facilitate the molecular diagnosis of CDA II by defining the frequency of mutations in each exon. Am. J. Hematol., 2010. © 2010 Wiley-Liss, Inc.

Molecular analysis of 42 patients with congenital dyserythropoietic anemia type II: new mutations in the SEC23B gene and a search for a genotype-phenotype relationship

BACKGROUND

The most frequent form of congenital dyserythropoietic anemia is the type II form. Recently it was shown that the vast majority of patients with congenital dyserythropoietic anemia type II carry mutations in the SEC23B gene. Here we established the molecular basis of 42 cases of congenital dyserythropoietic anemia type II and attempted to define a genotype-phenotype relationship.

DESIGN AND METHODS

SEC23B gene sequencing analysis was performed to assess the diversity and incidence of each mutation in 42 patients with congenital dyserythropoietic anemia type II (25 described exclusively in this work), from the Italian and the French Registries, and the relationship of these mutations with the clinical presentation. To this purpose, we divided the patients into two groups: (i) patients with two missense mutations and (ii) patients with one nonsense and one missense mutation.

RESULTS

We found 22 mutations of uneven frequency, including seven novel mutations. Compound heterozygosity for a missense and a nonsense mutation tended to produce a more severe clinical presentation, a lower reticulocyte count, a higher serum ferritin level, and, in some cases, more pronounced transfusion needs, than homozygosity or compound heterozygosity for two missense mutations. Homozygosity or compound heterozygosity for two nonsense mutations was never found.

CONCLUSIONS

This study allowed us to determine the most frequent mutations in patients with congenital dyserythropoietic anemia type II. Correlations between the mutations and various biological parameters suggested that the association of one missense mutation and one nonsense mutation was significantly more deleterious that the association of two missense mutations. However, there was an overlap between the two categories.

Mass spectrometry in the characterization of human genetic N-glycosylation defects

Human genetic diseases that affect N-glycosylation result from the defective synthesis of the N-linked sugar moiety (glycan) of glycoproteins. The role of glycans for proper protein folding and biological functions is illustrated in the variety and severity of clinical manifestations shared by congenital disorders of glycosylation (CDG). This family of inherited metabolic disorders includes defects in the assembly of the oligosaccharide precursor that lead to an under-occupancy of N-glycosylation sites (CDG-I), and defects of glycan remodeling (CDG-II). Mass spectrometry constitutes a key tool for characterization of CDG-I defects by mass resolution of native protein glycoforms that differ for glycosylation-site occupancy. Glycan MS analyses in CDG-II is mandatory to detect whenever possible a repertoire of structures to pinpoint candidate enzymes and genes responsible for the abnormal N-glycan synthesis. In this manuscript, we review the MS applications in the area of CDG and related disorders with a special emphasis on those techniques that have been already applied or might become functional for diagnosis, characterization, and treatment monitoring in some specific conditions.

Congenital dyserythropoietic anemia type II (CDAII/HEMPAS): where are we now?

Congenital diserythropoietic anemias (CDA) were classified according to bone marrow changes and biochemical features 40 years ago. A consistent finding in CDA type II, the most frequent subgroup of CDAs is a relevant hypoglycosylation of erythrocyte membrane proteins. It is a matter of debate if the hypoglycosylation is the primary cause of the disorder or a phenomenon secondary to other pathomechanisms. The molecular cause of the disorder is still unknown although some enzyme deficiencies have been proposed to cause CDA II in the last 2 decades and a linkage analysis locating the CDA II gene in a 5 cM region on chromosome 20 was done in 1997. In this review biochemical and genetic data are discussed and diagnostic methods based on biochemical observations of the recent years are reviewed.

Characterization of the N-glycosylation phenotype of erythrocyte membrane proteins in congenital dyserythropoietic anemia type II (CDA II/HEMPAS)

Congenital dyserythropoetic anemia type II (CDA II) is characterized by bi- and multinucleated erythroblasts and an impaired N-glycosylation of erythrocyte membrane proteins. Several enzyme defects have been proposed to cause CDA II based on the investigation of erythrocyte membrane glycans pinpointing to defects of early Golgi processing steps. Hitherto no molecular defect could be elucidated. In the present study, N-glycosylation of erythrocyte membrane proteins of CDA II patients and controls was investigated by SDS-Page, lectin binding studies, and MALDI-TOF/MS mapping in order to allow an embracing view on the glycosylation defect in CDA II. Decreased binding of tomato lectin was a consistent finding in all typical CDA II patients. New insights into tomato lectin binding properties were found indicating that branched polylactosamines are the main target. The binding of Aleuria aurantia, a lectin preferentially binding to alpha1-6 core-fucose, was reduced in western blots of CDA II erythrocyte membranes. MALDI-TOF analysis of band 3 derived N-glycans revealed a broad spectrum of truncated structures showing the presence of high mannose and hybrid glycans and mainly a strong decrease of large N-glycans suggesting impairment of cis, medial and trans Golgi processing.

CONCLUSION

Truncation of N-glycans is a consistent finding in CDA II erythrocytes indicating the diagnostic value of tomato-lectin studies. However, structural data of erythrocyte N-glycans implicate that CDA II is not a distinct glycosylation disorder but caused by a defect disturbing Golgi processing in erythroblasts.

Glycoproteomics ofN-glycosylation by in-gel deglycosylation and matrix-assisted laser desorption/ionisation-time of flight mass spectrometry mapping: Application to congenital disorders of glycosylation

A general strategy for the structural evaluation of N-glycosylation, a common post-translational protein modification, is presented. The methods for the release of N-linked glycans from the gel-separated proteins, their isolation, purification and matrix-assisted laser desorption/ionisation-mass spectrometry (MALDI-MS) analysis of their mixtures were optimised. Since many glycoproteins are available only at low quantities from sodium dodecyl sulphate-polyacrylamide gel electrophoresis or two-dimensional gels, high attention was paid to obtain N-glycan mixtures representing their actual composition in human plasma by in-gel deglycosylation. The relative sensitivity of solid MALDI matrices for MS analysis of acidic N-glycans was compared. The most favourable results for native acidic N-glycans were obtained with 2,4,6-trihydroxyacetophenone monohydrate/diammoniumcitrate as a matrix. This matrix provided good results for both neutral and acidic mixtures as well as for methylated N-glycans. In the second part of this paper the potential of such an optimised MS strategy alone or in combination with high pH anion-exchange chromatography profiling for the clinical diagnosis of congenital disorders of glycosylation is presented.

Congenital dyserythropoietic anemia type II: epidemiology, clinical appearance, and prognosis based on long-term observation

Congenital dyserythropoietic anemia type II (CDA II) is the most frequent type of congenital dyserythropoietic anemia. More than 200 cases have been described, but with the exception of a report by the International CDA II Registry, these reports include only small numbers of cases and no data on the lifetime evolution of the disease. Since 1967, we were able to follow 48 cases of CDA II from 43 families for up to 35 years. All patients exhibit chronic anemia of variable severity requiring regular red cell transfusions only in a minority of children; 60% developed gallstones before the age of 30 years, and 16 patients had cholecystectomy between 8 and 34 years of age. Iron overload was a frequent complication. In 16 cases, iron depletion started between 7 and 36 years. Three patients died from secondary hemochromatosis. Splenectomy, performed in 22 cases, led to moderate increases in hemoglobin values and eliminated the need for transfusions but did not prevent further iron loading. The current recommendation is to consider splenectomy if the anemia compromises patients' performance, and to manage iron overload according to the guidelines derived from patients with thalassemia.

Congenital dyserythropoietic anaemia type II (HEMPAS) and haemochromatosis: a report of two cases

We describe two patients with severe iron overload in the context of congenital dyserythropoietic anaemia (CDA) type II, which is characterized by a protein glycosylation defect with impairment of N-glycan synthesis. In both patients a corpuscular, haemolytic anaemia had been diagnosed in early childhood and both patients underwent splenectomy before the age of 9 years. They developed clinical manifestations of haemochromatosis and only re-evaluation during adulthood led to the correct diagnosis. Abnormal glycosylation of proteins involved in iron homeostasis is likely to contribute to the massive hepatic iron accumulation characteristic for CDA type II. Both patients required chelation therapy. This report points out the need to consider CDA in patients presenting with haemochromatosis and anaemia.

A case of congenital dyserythropoietic anemia type II, Gilbert's syndrome and malleolar trophic ulcers

A case of a woman with congenital dyserythropoietic anemia type II (CDA-II), Gilbert's syndrome (GS) and trophic malleolar ulceration is described. The association of CDA-II and GS caused early gallstone formation that led the patient to undergo cholecystectomy at the age of 15. GS is typified by increased production of both unconjugated and monoconjugated bilirubin, which is more lithogenic. The development of ulcers is not typical of CDA-II, even though they are associated with many of the hemolytic anemias, and were thought in our patient to be due to a thrombophilic tendency which manifest with Antithrombin III and Protein C deficiency.

Congenital dyserythropoietic anemia type II: exclusion of seven candidate genes

Congenital dyserythropoietic anemias (CDA) are genetic disorders characterized by anemia and ineffective erythropoiesis. Three main types of CDA have been distinguished: CDA I, CDAII and CDA III, whose loci have been already mapped. After the identification of the locus for CDA II, also known as HEMPAS (hereditary erythroblast multinuclearity with positive acidified serum test), on the long arm of chromosome 20 (20q11.2) we have analyzed by a mutational search seven candidate genes in a large series of CDA II patients. In particular, the following genes have been investigated: integrin beta 4 binding protein, ribophorin II, ubiquitin protein ligase ITCH, mannosil-oligosaccharide alpha-1,2-mannosidase like protein, erythrocyte protein band 4.1 like protein, zinc finger protein PLAGL2, and finally novel zinc finger protein. None of them resulted as the causative gene but several protein variants and DNA polymorphisms have been identified. These data exclude the role of the above mentioned genes in causing CDA II and add further information in the process of cloning the CDA II gene.

HEMPAS. Hereditary erythroblastic multinuclearity with positive acidified serum lysis test

Congenital dyserythropoietic anemia type II or HEMPAS (hereditary erythroblastic multinuclearity with positive acidified serum lysis test) is a genetic anemia in humans caused by a glycosylation deficiency. Erythrocyte membrane glycoproteins, such as band 3 and band 4.5, which are normally glycosylated with polylactosamines lack these carbohydrates in HEMPAS. Polylactosamines accumulate as glycolipids in HEMPAS erythrocytes. Analysis of N-glycans from HEMPAS erythrocyte membranes revealed a series of incompletely processed N-glycan structures, indicating defective glycosylation at N-acetylglucosaminyltransferase II (GnT-II) and/or alpha-mannosidase II (MII) steps. Genetic analysis has identified two cases from England in which the MII gene is defective. Mutant mice in which the MII gene was inactivated by homologous recombination resulted in a HEMPAS-like phenotype. On the other hand, linkage analysis of HEMPAS cases from southern Italy excluded MII and GnT-II as the causative gene, but identified a gene on chromosome 20q11. HEMPAS is therefore genetically heterogeneous. Regardless of which gene is defective, HEMPAS is characterized by incomplete processing of N-glycans. The study of HEMPAS will identify hitherto unknown factors affecting N-glycan synthesis.

Suppression of CDA II expression in a homozygote

The CDAN2 gene, responsible for congenital dyserythropoietic anaemia, type II (CDA II), was recently mapped to 20q11.2. We report data on an additional member of a previously studied CDA II family. This member had always been regarded as haematologically normal. Unexpectedly, she had the same microsatellite assortments around the CDAN2 alleles as her three sisters with CDA II. In particular, she was a homozygote for microsatellites D20S863 and D20S841. This prompted an analysis of all facets of her phenotype. The Ham test was negative. The bone marrow smears contained a normal proportion of binucleate erythroblasts. Electron microscopy revealed the absence of extensive stretches of cisternae beneath and parallel to the inner surface of the erythroblast plasma membrane. Proteins of the endoplasmic reticulum, which contaminate the reticulocyte plasma membrane in CDA II patients, were missing. Only the shape of the band 3 peak appeared slightly altered. This case exemplifies that homozygosity (or compound heterozygosity) for a deleterious gene may be silenced, or almost completely silenced. In recessively inherited diseases, suppressed phenotypes tend to be overlooked in siblings where both patients and unaffected individuals are expected.

Exclusion of Three Candidate Genes as Determinants of Congenital Dyserythropoietic Anemia Type II (CDA-II)

Congenital dyserythropoietic anemia type II (CDA-II) is the most common form of inherited dyserythropoiesis. Previous studies have shown that the anion transporter (band 3) is narrower and it migrates faster on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE); this aspect was related to insufficient glycosylation. Biochemical data support the hypothesis that this disease is due to a deficiency of N-acetylglucosaminyltransferase II (GnT II) or α-Mannosidase II (α-Man II), which represent the key to glycosylation. In addition, a third candidate gene is α-Man IIx, which shows a strong homology with α-Man II. The knowledge of the chromosomal localization of these putative genes allowed us to perform a linkage study using three sets of microsatellite markers flanking the candidate genes. Six families with two or more affected children were enrolled in this study. The data obtained exclude linkage to all three candidate genes. In consideration of the biochemical data (reduction of enzymatic activity) of the same enzymes, our results suggest the hypothesis that a defect in an unknown transcriptional factor is involved in CDA-II.

Localization of the congenital dyserythropoietic anemia II locus to chromosome 20q11.2 by genomewide search

Congenital dyserythropoietic anemias (CDA) are genetic disorders characterized by anemia and ineffective erythropoiesis. Three main types of CDA have been distinguished: CDA I and CDA III, whose loci have been already mapped, and CDA II (MIM 224100), the most frequent among CDAs, which is transmitted as an autosomal recessive trait and is known also as "HEMPAS" (hereditary erythroblast multinuclearity with positive acidified serum). We have recruited a panel of well-characterized CDA II families and have used them to search for the CDA II gene by linkage analysis. After the exclusion of three candidate genes, we ob-tained conclusive evidence for linkage of CDA II to microsatellite markers on the long arm of chromosome 20 (20q11.2). A maximum two-point LOD score of 5.4 at a recombination fraction of .00 was obtained with marker D20S863. Strong evidence of allelic association with the disease was detected with the same marker. Some recombinational events established a maximum candidate interval of approximately 5 cM.

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.

Acral dysostosis dyserythropoiesis syndrome

The term congenital dyserythropoietic anaemia (CDA) designates a group of rare but well defined erythrocytic disorders. Type I is defined by macrocytosis and megaloblastic changes of the bone marrow cells. Two unrelated children with CDA are described with associated defects: absence of nails and short or absent phalanges, polysyndactyly of the fourth metacarpal. One of them had also areas of depigmentation.

CONCLUSION

The association of congenital dyserythropoietic anaemia with morphological defects of hands and feet is suggested to constitute a new syndrome caused by a single morphogenetic gene.

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.

Incompletely processed N-glycans of serum glycoproteins in congenital dyserythropoietic anaemia type II (HEMPAS)

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.

Congenital dyserythropoiesis and progressive alopecia in Polled Hereford calves: hematologic, biochemical, bone marrow cytologic, electrophoretic, and flow cytometric findings

Congenital dyserythropoiesis with dyskeratosis is a slow, progressive, and often fatal disease in Polled Hereford calves. Affected calves have a macrocytic normochromic anemia with a mild reticulocytosis. Studies indicate that calves are hyperferremic with increased saturation of serum total iron binding capacity, which rules out iron deficiency as a cause. Other secondary causes of dyserythropoiesis, including cobalamin and folate deficiencies, are unlikely because serum cobalamin and folate levels of affected calves were normal. Virus isolation was negative, and failure to identify bovine retroviral antigens or antibodies from several calves suggested that viral agents were not involved. Bone marrow cytologic findings were similar to those in congenital hereditary dyserythropoiesis in humans and included occasional multinucleate cells, internuclear chromatin bridging between nuclei of partially divided cells, and, more frequently, irregular nuclear shapes and chromatin patterns. DNA content and cell cycle distribution of erythroid cells appeared normal, and no electrophoretic abnormalities were detected in erythrocyte membrane proteins. The Polled Hereford syndrome is similar in many ways to type I congenital dyserythropoiesis in humans and may be an appropriate biomedical model for studying erythroid proliferation during dyserythropoiesis.

Circulating nucleated red blood cells following splenectomy in a patient with congenital dyserythropoietic anemia

A 24-year-old white female with a 10-year history of juvenile rheumatoid arthritis and splenomegaly developed numerous circulating nucleated red blood cells (NRBC) following splenectomy for chronic abdominal pain. Subsequent evaluation revealed the presence of a congenital dyserythropoietic anemia (CDA) with atypical features. Circulating NRBCs have been reported following splenectomy in three other cases of CDA, each of which had atypical features and did not fit into the customary classification of types I-IV. Follow-up of our patient at 4 years revealed no untoward consequences of persistent NRBCs in her circulation.

Primary shunt hyperbilirubinaemia: a variant of the congenital dyserythropoietic anaemias

A 19 year old Mauritian male presented with episodic nausea, abdominal discomfort and jaundice. Unconjugated hyperbilirubinaemia and erythroid hyperplasia without dyserythropoiesis led to the diagnosis of primary shunt hyperbilirubinaemia. The similarity between congenital dyserythropoietic anaemia and this entity suggests that patients with these lesions can be considered within a single spectrum of disorders, characterized as congenital ineffective erythropoiesis.

Incomplete synthesis of N-glycans in congenital dyserythropoietic anemia type II caused by a defect in the gene encoding alpha-mannosidase II

Congenital dyserythropoietic anemia type II, or hereditary erythroblastic multinuclearity with a positive acidified-serum-lysis test (HEMPAS), is a genetic anemia in humans inherited by an autosomally recessive mode. The enzyme defect in most HEMPAS patients has previously been proposed as a lowered activity of N-acetylglucosaminyltransferase II, resulting in a lack of polylactosamine on proteins and leading to the accumulation of polylactosaminyl lipids. A recent HEMPAS case, G.C., has now been analyzed by cell-surface labeling, fast-atom-bombardment mass spectrometry of glycopeptides, and activity assay of glycosylation enzymes. Significantly decreased glycosylation of polylactosaminoglycan proteins and incompletely processed asparagine-linked oligosaccharides were detected in the erythrocyte membranes of G.C. In contrast to the earlier studied HEMPAS cases, G.C. cells are normal in N-acetylglucosaminyltransferase II activity but are low in alpha-mannosidase II (alpha-ManII) activity. Northern (RNA) analysis of poly(A)+ mRNA from normal, G.C., and other unrelated HEMPAS cells all showed double bands at the 7.6-kilobase position, detected by an alpha-ManII cDNA probe, but expression of these bands in G.C. cells was substantially reduced (less than 10% of normal). In Southern analysis of G.C. and normal genomic DNA, the restriction fragment patterns detected by the alpha-ManII cDNA probe were indistinguishable. These results suggest that G.C. cells contain a mutation in alpha-ManII-encoding gene that results in inefficient expression of alpha-ManII mRNA, either through reduced transcription or message instability. This report demonstrates that HEMPAS is caused by a defective gene encoding an enzyme necessary for the synthesis of asparagine-linked oligosaccharides.

Aberrant pattern of red cell membrane and cytosolic proteins in a case of congenital dyserythropoietic anaemia

We report an unusual case of congenital dyserythropoietic anaemia (CDA). The propositus is a 25-year-old gipsy female presenting with a recessively inherited haemolytic anaemia. The diagnosis of CDA was based on erythrokinetic data and the morphological appearance of the erythroid precursors. The direct assay of HEMPAS antigen was negative. In peripheral blood there were 15% dacryocytes. The red cell membrane protein pattern was dramatically altered, with four major aberrant bands. Band a (mol wt 86,000) was at the lower edge of band 3, band b (mol wt 82,000) was below band 3, band c (68,000) and band d (67,000) were below band 4.2. In addition, there was an array of aberrant minor bands below band d. Gel densitometric determinations and immunological characterization showed that these bands did not derive from any of the major components of the membrane. In fact, membrane proteins appeared normal in many respects, although periodic acid-Schiff staining revealed an apparent decrease of sialoglycoproteins. The major aberrant bands a, b and c occur in very low amounts in controls. These bands, as well as band d, also exist in normal cytosol and were strongly increased in the propositus.

Glycolipids and glycopeptides of red cell membranes in congenital dyserythropoietic anaemia type II (CDA II)

The composition and structure of neutral and acidic oligoglycosylceramides, polyglycosylceramides and polyglycosylpeptides were determined in erythrocyte membranes of two patients with congenital dyserythropoietic anaemia type II. In keeping with previous studies we found an elevated accumulation in CDA II erythrocytes of LacCer, Lc3Cer and nLc4Cer. Gb4Cer was elevated in erythrocytes of only one of the two patients tested. In addition we found a significant increase of 6IVNeuAcnLc4Cer ganglioside. Polyglycosylceramides were elevated 6-fold but they resembled those of cord erythrocytes with respect to complexity and the number of side chains. Polyglycosylpeptides of CDA II erythrocytes were decreased 7-fold. These glycopeptides were, however, heterogeneous with respect to branching pattern; the minor fraction was highly branched whereas the major one was more linear in structure. Both polyglycosylceramides and polyglycosylpeptides exhibited high I and i antigenicity. We postulate that the accumulation of glycolipids and underglycosylation of glycoproteins in CDA II membranes results from the prolongation of G1 and possibly M phases of the mitotic cycle of the erythroid cells in which glycolipids are preferentially synthesized.

Unclassified type of congenital dyserythropoietic anaemia (CDA) with prominent peripheral erythroblastosis

Two unrelated cases of congenital dyserythropoietic anaemia (CDA) are described. They show striking similarities which could not be attributed to one of the well-known types of CDA or any other congenital disease of the erythroid system. Both patients were followed for many years before and after splenectomy. There was a long-lasting, prominent post-splenectomy erythroblastosis, suggesting impairment of red cell denucleation. The type of heredity is unknown, and the enzymatic or molecular basis of the changes observed is not understood.

Abnormality of glycophorin-alpha on paroxysmal nocturnal hemoglobinuria erythrocytes

To investigate the greater enzymatic activity of the alternative pathway convertase (and the subsequent greater fixation of C3b) on paroxysmal nocturnal hemoglobinuria (PNH) erythrocytes, we have examined the topography of binding of C3b to PNH and normal erythrocytes. Using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography, the alpha-chain of C3b was found to bind via predominantly ester bonds to free hydroxyl groups on glycophorin-alpha, the major erythrocyte sialoglycoprotein. The pattern of binding of nascent C3b was the same for normal and PNH erythrocytes. Thus, although C3b binding to a different membrane constituent did not appear to account for the greater enzymatic activity of the alternative pathway convertase when affixed to PNH erythrocytes, it seemed possible that the glycoproteins to which C3b bound might be qualitatively abnormal on the PNH cells, and that structural differences in these molecules might impose modifications in the enzyme-substrate interactions of the alternative pathway convertase. Using methods for radiolabeling both protein and carbohydrate residues, we therefore compared the electrophoretic pattern of the cell-surface glycoproteins on PNH and normal erythrocytes. The glycophorin-alpha dimer was found to be qualitatively abnormal on the PNH cells as evidenced by its greater susceptibility to trypsin-mediated proteolysis. In addition, the abnormal erythrocytes from patients with PNH had fewer periodate oxidizable constituents than did normal erythrocytes, indicating a relative deficiency of cell-surface sialic acid. These investigations suggest that abnormalities in membrane glycoproteins may underlie the aberrant interactions of complement with the hematopoietic elements of PNH.

Defect in glycosylation of erythrocyte membrane proteins in congenital dyserythropoietic anaemia type II (HEMPAS)

Congenital dyserythropoietic anaemia type II (HEMPAS) is a hereditary disease believed to be caused by a membrane abnormality of erythroid cells. Since the molecular basis of this membrane abnormality has not yet been defined, membrane glycoproteins of HEMPAS erythrocytes were analysed by cell surface labelling and endo-beta-galactosidase digestion in this study. HEMPAS erythrocytes showed an abnormal glycoprotein profile when cells were labelled by the galactose oxidase/NaB[3H]4 method; Band 3 and Band 4.5 glycoproteins in HEMPAS are labelled but with less intensity although normally these proteins are the major components revealed by the same method. Instead, in HEMPAS, labelled lactosaminoglycans were found as a lower molecular weight glycoconjugate (HEMPAS glycan). HEMPAS glycan was characterized by micelle formation, a monomer molecular weight of 4000, susceptibility to endo-beta-galactosidase and resistance to protease. These characteristics suggest that HEMPAS glycan has the nature of macroglycolipid. Proteins of Band 3 and the glucose transport protein (a component of Band 4.5), which were detected by antibodies showed a slightly decreased molecular weight in HEMPAS erythrocytes compared to those from normal erythrocytes, which was consistent with the decreased glycosylation of these proteins. The results indicate that anomalies in glycosylation occurred specifically in lactosaminoglycan glycoproteins of HEMPAS erythrocytes.

Incomplete glycosylation of erythrocyte membrane proteins in congenital dyserythropoietic anaemia type II (CDA II)

The alterations in the erythrocyte membrane proteins of individuals with congenital dyserythropoietic anaemia (CDA II) were studied. Alterations were observed in both the erythrocyte sialoglycoproteins and erythrocyte anion transport protein (Band 3). There was a decrease in the apparent molecular weight of the major sialoglycoprotein alpha (glycophorin A) as well as a general reduction in the intensity of staining of all the sialoglycoproteins by the PAS stain. Sialoglycoprotein alpha isolated from CDA II erythrocytes contained 30% less sialic acid than normal alpha. The anion transport protein of CDA II erythrocytes migrated as a band with a lower molecular weight than the normal protein on SDS-gel electrophoresis. The CDA II anion transport protein had a substantially reduced content of N-acetylglucosamine and galactose, which probably reflects a reduction in the number of N-acetyl-lactosamine units carried by the protein. Our results suggest that there is a general defect in glycosylation of the major membrane glycoproteins of CDA II erythrocytes. We suggest that this glycosylation defect is a consequence of bone marrow stress.

Decreased glycosylation of band 3 and band 4.5 glycoproteins of erythrocyte membrane in congenital dyserythropoietic anaemia type II

We report a study of HEMPAS erythrocyte membrane glycoproteins in relation to proteolytic digestion and surface labelling with galactose-oxidase/NaB[3H]4. The proteolytic digestion of band 3, the major intrinsic glycoprotein of the human erythrocyte membrane, reveals an abnormality in the outer glycosylated segment of this protein. 3H incorporation in band 3 and band 4.5 glycoproteins after treatment with galactose-oxidase/NaB[3H]4 is reduced in HEMPAS red cells suggesting a defective glycosylation of these proteins. These findings together with the persistence of i antigen and the normal presence of I antigen lead us to conclude that erythroblastic membrane features may persist in HEMPAS erythrocytes.

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.

Erythrocyte membrane proteins in an unusual case of congenital dyserythropoietic anaemia type II (CDA II)

Analysis of the erythrocyte membrane protein of an atypical case of congenital dyserythropoietic anaemia type II (CDA II) by electrophoresis on polyacrylamide gels revealed marked abnormalities. One-dimensional analysis showed a pronounced decrease in levels of B1.1 components, an increase in the level of B1.4 and the appearance of new components in the A region as well as in the C region of the gel. There were no artefacts due either to the presence of early red cells or to abnormally high levels of proteolytic enzyme activity in the CDA II preparations. Two-dimensional analysis confirmed the alterations in membrane components showing two novel A region species not reported in other studies of this disease. Abnormalities in components of such large molecular size may explain the greater degree of membrane perturbation seen in the present case and support the idea that CDA II may embrace more than one disease entity.

Congenital dyserythropoietic anemia type I. Report of a case

A new case of congenital dyserythropoietic anemia type I is reported in a 12-year-old Spanish boy. In regard to the morphological study at an optical and ultrastructural level, the most outstanding feature was the internuclear bridging connecting two erythroblastic nuclei within a single cytoplasm or stretched between two erythroblasts perfectly individualized.