EXPANDING THE MOLECULAR MECHANISMS AND THE PATIENT COHORT IN CONGENITAL DYSERYTHROPOIETIC ANEMIA III

​Background: Congenital Dyserythropoietic Anemia type III (CDA III), the rarest subtype in the CDA spectrum, includes autosomal dominant CDA IIIa with monoallelic KIF23 mutations and recessive CDA IIIb with biallelic RACGAP1 missense mutations, as we recently shown. Limited documented cases hinder a complete understanding of the syndrome, posing challenges in accurate diagnosis due to its rarity.

Aims: To report new patients affected by CDAIIIb and characterize the cellular and clinical abnormalities associated with mutations in the RACGAP1 protein.

Methods: DNA samples were collected from five Argentinian individuals with clinical features suggestive of CDAIIIb, along with healthy relatives. We conducted targeted Next-Generation Sequencing (NGS) using a comprehensive panel covering all CDA-associated genes. In addition, in vitro assays with cell lines were performed to assess the impact of missense mutations in the RACGAP1 protein. These assays focused on evaluating the protein's centralspindlin complex formation ability and its capacity to modulate key GTPases essential for cytokinesis progression.

Results: All patients displayed typical CDAIII symptoms, including macrocytic anemia, hemolysis (increased bilirubin and LDH with absence of haptoglobin), and giant multinucleated erythroblasts in the bone marrow. Surprisingly, all affected individuals were homozygous for the known Pro432Ser mutation, while healthy relatives were carriers. In vitro findings reveal that the Pro432Ser and Thr220Ala mutations do not hinder centralspindlin complex formation or localization. However, they disrupt its ability to accurately modulate the activation status of RHOA, CDC42, and RAC1 GTPases.

​Supported by grants PID2021-122436OB-I00 and grant RTC2019-007074-1 from MCIN/AEI /10.13039/501100011033 to MS.