Congenital dyserythropoietic anemia type II: exclusion of seven candidate genes

Pleomorphic adenoma gene like-2 induces epithelial-mesenchymal transition via Wnt/β-catenin signaling pathway in human colorectal adenocarcinoma

Epithelial-mesenchymal transition (EMT) is a critical step in the acquisition of metastatic and invasive power for tumor cells. Colorectal adenocarcinoma (CRC) is a common cancer where metastasis is directly linked to patient survival. Recent studies show that pleomorphic adenoma gene like-2 (PLAGL2) could induce tumor EMT and is an independent predictive factor associated with poor prognosis in cancer. In the present study, we confirmed the role of PLAGL2 in the prognosis of CRC patients and provide molecular evidence of PLAGL2 promoted EMT in CRC cell line SW480. We found that PLAGL2 expression was upregulated in the paraffin-embedded CRC tissues compared to borderline or benign tissues. Experimental EMT induced by PLAGL2 plasmid transfection proved PLAGL2 protein overexpression could enhance the cell scratch wound-healing and Transwell ability and significantly upregulated mesenchymal marker proteins, N-cadherin and vimentin and concurrently downregulated epithelial marker of E-cadherin. Subsequently, through western blot assay, we found that PLAGL2 could activate the Wnt-signaling component β-catenin in the nuclei. More CRC cell metastasis to the lungs was observed when the PLAGL2 overexpressing SW480 cells were injected into the tail vein of rats, compared with the cell control and PLAGL2 silence group. Our findings indicated that PLAGL2 might be a very upstream key molecule regulating EMT involved in Wnt/β-catenin signaling pathway.

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.

Congenital dyserythropoietic anemia

Congenital dyserythropoietic anemias (CDAs) are a heterogeneous group of rare hereditary disorders of erythropoiesis characterized by morphologic abnormal erythroblasts in the bone marrow. Three types of the disease are known as type I, II and III, and the variant type of CDA and several minor subgroups of CDA have been also reported since the first classification. Recently, responsible genes for type I (CDAN1) and type II (SEC23B) have been identified and the molecular pathogenesis of the disease is currently being explored. Although CDAs rarely transform to myelodysplastic syndrome or leukemia, the disease is important to understand the mechanism of hemopoiesis in humans.

A novel missense mutation in MVK associated with MK deficiency and dyserythropoietic anemia

Mevalonate kinase deficiency (MKD) is a rare inborn error of metabolism caused by mutations in the mevalonate kinase (MVK) gene. The clinical phenotype is variable, ranging from the hyperimmunoglobulinemia D and periodic fever syndrome (HIDS) to mevalonic aciduria (MA), a severe metabolic disease. We report here for the first time (to our knowledge) the case of a patient with MKD and congenital dyserythropoietic anemia. Clinical and laboratory characteristics of inflammatory attacks were compatible with HIDS, but mild dysmorphic features and elevated urinary mevalonic acid levels in the absence of an inflammatory attack suggested an intermediate phenotype between HIDS and MA. Genomic sequencing of the MVK gene revealed compound heterozygosity for a missense mutation previously described in MA (V310M) and a novel missense mutation (Y116H). By contrast, sequencing of the novel CDAII (SEC23B) gene revealed no mutations, suggesting that the bone marrow abnormalities were causally related to the MKD. Treatment with corticosteroids and colchicine directed at controlling the autoinflammatory disease resulted in improvement of the anemia.

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.

Close to unraveling the secrets of congenital dyserythropoietic anemia types I and II

The congenital dyserythropoietic anemias are rare recessive disorders characterized by erythroblast multinuclearity, ineffective erythropoiesis, anemia and iron overload. In this perspective article, Drs. Iolascon and Delaunay examine genetic and clinical aspects of these inherited disorders.

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.

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.

Glycosylation diseases: quo vadis?

About 250 to 500 glycogenes (genes that are directly involved in glycan assembly) are in the human genome representing about 1-2% of the total genome. Over 40 human congenital diseases associated with glycogene mutations have been described to date. It is almost certain that the causative glycogene mutations for many more congenital diseases remain to be discovered. Some glycogenes are involved in the synthesis of only a specific protein and/or a specific class of glycan whereas others play a role in the biosynthesis of more than one glycan class. Mutations in the latter type of glycogene result in complex clinical phenotypes that present difficult diagnostic problems to the clinician. In order to understand in biochemical terms the clinical signs and symptoms of a patient with a glycogene mutation, one must understand how the glycogene works. That requires, first of all, determination of the target protein or proteins of the glycogene followed by an understanding of the role, if any, of the glycogene-dependent glycan in the functions of the protein. Many glycogenes act on thousands of glycoproteins. There are unfortunately no general methods to identify all the potentially large number of glycogene target proteins and which of these proteins are responsible for the mutant phenotypes. Whereas biochemical methods have been highly successful in the discovery of glycogenes responsible for many congenital diseases, it has more recently been necessary to use other methods such as homozygosity mapping. Accurate diagnosis of many recently discovered diseases has become difficult and new diagnostic procedures must be developed. Last but not least is the lack of effective treatment for most of these children and of animal models that can be used to test new therapies.

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.

Congenital Disorders of Glycosylation: A Rapidly Expanding Disease Family

Congenital disorders of glycosylation (CDG) are a large family of genetic diseases resulting from defects in the synthesis of glycans and in the attachment of glycans to other compounds. These disorders cause a wide range of human diseases, with examples emanating from all medical subspecialties. Since our 2001 review on CDG ( 36 ), this field has seen substantial growth: The number of N-glycosylation defects has doubled (from 6 to 12), five new O-glycosylation defects have been added to the two previously known ones, three combined N- and O-glycosylation defects have been identified, the first lipid glycosylation defects have been discovered, and a new domain, that of the hyperglycosylation defects, has been introduced. A number of CDG are due to defects in enzymes with a putative glycosyltransferase function. There is also a growing group of patients with unidentified defects (CDG-x), some with typical clinical presentations and others with presentations not seen before in CDG. This review focuses on the clinical, biochemical, and genetic characteristics of CDG and on advances expected in their future study and clinical management.

Mammalian N-glycan branching protects against innate immune self-recognition and inflammation in autoimmune disease pathogenesis

Autoimmune diseases are prevalent and often life-threatening syndromes, yet the pathogenic triggers and mechanisms involved remain mostly unresolved. Protein asparagine linked- (N-) glycosylation produces glycan structures that substantially differ among the extracellular compartments of evolutionarily divergent organisms. Alpha-mannosidase-II (alphaM-II) deficiency diminishes complex-type N-glycan branching in vertebrates and induces an autoimmune disease in mice similar to human systemic lupus erythematosus. We found that disease pathogenesis provoking glomerulonephritis and kidney failure was nonhematopoietic in origin, independent of complement C3 and the adaptive immune system, mitigated by intravenous administration of immunoglobulin-G, and linked to chronic activation of the innate immune system. N-glycans produced in alphaM-II deficiency bear immune-stimulatory mannose-dependent ligands for innate immune lectin receptors, disrupting the phylogenic basis of this glycomic recognition mechanism. Thus, mammalian N-glycan branching safeguards against the formation of an endogenous immunologic signal of nonself that can provoke a sterile inflammatory response in the pathogenesis of autoimmune disease.

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.

Stomatocytic haemolysis and macrothrombocytopenia (Mediterranean stomatocytosis/macrothrombocytopenia) is the haematological presentation of phytosterolaemia

Phytosterolaemia (sitosterolaemia) is a recessively inherited metabolic condition in which the absorption of both cholesterol and plant-derived cholesterol-like molecules at the gut is unselective and unrestricted. In haematology, Mediterranean stomatocytosis or Mediterranean macrothrombocytopenia is a poorly understood haematological condition that combines stomatocytic haemolysis with the presence of very large platelets. Five pedigrees showing this haematology were identified. Gas chromatography mass spectrometry (GC-MS) showed that all of the patients with this highly specific haematology had grossly elevated levels of phytosterols in the blood, diagnostic of phytosterolaemia. All showed mutations in the ABCG5 and ABCG8 previously linked to phytosterolaemia. Three pedigrees showed five new mutations, while two pedigrees showed the common W361X mutation in ABCG8. We draw the following four conclusions: (i) that Mediterranean stomatocytosis/macrothrombocytopenia is caused by an excess of phytosterols in the blood; (ii) that phytosterolaemia, which does not respond to standard statin treatment, can be diagnosed via the distinctive haematology described here, even when the cholesterol is normal; (iii) that phytosterolaemia should be considered in the differential diagnosis of all patients with large platelets; and (iv) that the platelet size should be noted in patients with hypercholesterolaemia.