A rare congenital anemia is caused by mutations in the centralspindlin complex

Congenital dyserythropoietic anemias (CDAs) are rare disorders characterized by morphologic abnormalities of erythroid precursors leading to ineffective erythropoiesis. CDA type III (CDAIII), characterized by erythroblast multinucleation, represents the rarest form with only ∼60 patients described in the literature. Previous work, studying two independent families, identified a causative dominant missense mutation in KIF23 , which encodes for the kinesin MKLP1. Here, we describe a sporadic CDAIII case associated with compound heterozygous variants in RACGAP1 , a gene not previously associated with any disease. RACGAP1 encodes CYK4, a GTPase activating protein (GAP) for Rho-family GTPases, which interacts with MKLP1 to form the centralspindlin complex. Functional assays show these RACGAP1 variants cause cytokinesis defects due, at least in part, to altering the substrate specificities of the GAP activity of CYK4. These findings provide novel insights into the structural determinants of the GAP activity and demonstrates that cytokinesis failure due to centralspindlin defects leads to CDAIII. Our findings highlight the importance of viewing diseases as malfunctions of common biological pathways/complexes and suggests that next-generation sequencing analysis pipelines should integrate a systems approach in order to identify such functionally related variants. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported by 1K08NS119567 to SNW and a Cancer Research UK program grant (C19769/ A11985) to MM. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The Columbia University Irving Medical Center IRB deemed the work as exempt. All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Requests for any data presented can be obtained through contacting the corresponding authors.