CONGENITAL DYSERYTHROPOIETIC ANEMIA TYPE II: GENOTYPE-PHENOTYPE CORRELATION, MOLECULAR MECHANISMS, ANIMAL MODEL. NEW INSIGHTS IN ERYTHROPOIESIS AND IRON OVERLOAD

Congenital Dyserythropoietic Anemias (CDAs) are a heterogeneous group of inherited disorders in which anemia of variable severity is present without other cytopenias. Three forms of CDAs are well known (Heimpel and Wendt, 1967): the type II is the well biochemically characterized and known, as well as the most frequent form. Cirrhosis and hemochromatosis of the liver, diabetes and gallstones are common complications. CDA II is associated with a well defined cellular and ultrastructural phenotype: bi- or multi-nucleated late precursors, flat vesicles of variable length, abnormalities affecting glycosylation and/or levels of erythrocyte glycoconjugates. The causative gene (CDAN2), localized on 20p11.2, was recently identified by two independent approaches, the positional and functional mapping (Nature Genetics submitted). This discovery opens a wide range of studies direct to acquire new insights in erythropoiesis and also in overcome CDA II complications, such as iron overload. In particular, CDAN2 identification could allow heterozygous state diagnosis and prenatal diagnosis, planning of lifelong therapy and follow-up, preventing organ damage, studying genotype-phenotype correlation. We plan to elucidate the molecular genetics of CDA II by CDAN2 sequencing analysis of all CDA II cases, by studying geographic clustering of its mutations, and by analyzing the role of CDAN2 in erythropoiesis through gene promoter analysis. Moreover, we aim to understand the molecular mechanisms through which CDAN2 alterations cause CDA II by in vitro functional studies on two cellular models: CDA34+ during erythroid differentiation and human hepatoma cell line, HepG2, since in CDAII patients defects in protein glycosylation were detected in epatocytes (Fukuda, 1992). Finally, we plan to generate knock-out (KO) and knock-in (KI) mouse models to acquire insights on CDA II molecular mechanisms, clarifying the unique role(s) or redundant role(s) in which CDAN2 protein is involved. Furthermore, if animal models are able to reproduce the clinical features of CDA II patients, they could allow to evaluate possible therapeutical approaches.