Lack of the human choline transporter-like protein CTL2 causes hearing impairment and a rare red blood cell phenotype

Recent genome-wide association and murine studies identified the human neutrophil antigen -3a/b polymorphism (HNA-3a/b) in SLC44A2 (rs2288904-G/A) as a risk factor in venous thromboembolism (VTE). The choline transporter-like protein CTL2 encoded by the SLC44A2 gene plays an important role in platelet aggregation and neutrophil interaction with the von Willebrand factor. By investigating alloantibodies to a high-prevalence antigen of unknown specificity, found in patients with a rare blood type, we showed that CTL2 is also expressed in red blood cells and carries a new blood group system. Furthermore, we identified three siblings of European ancestry who are homozygous for a large deletion in SLC44A2 , resulting in complete CTL2 deficiency. Interestingly, the first-ever reported CTL2-deficient individuals suffer from progressive hearing impairment, recurrent arterial aneurysms and epilepsy. In contrast to Slc44a2 -/- mice, CTL2null individuals showed normal platelet aggregation and do not suffer from any apparent hematological disorders. In addition, CD34+ cells from CTL2null patients undergo normal ex vivo erythropoiesis, indicating that CTL2 is not essential for erythroid proliferation and differentiation. Overall, our findings confirm the function of CTL2 in hearing preservation and provide new insights into the possible role of this protein in maintaining cerebrovascular homeostasis. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement a grant from Association Recherche et Transfusion (#151/2016), the Institut National de la Transfusion Sanguine, and the Laboratory of Excellence GR-Ex, reference ANR-11-LABX-0051; GR-Ex is funded by the program Investissements d avenir of the French National Research Agency, reference ANR-11-IDEX-0005-02. ### 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: Ethics committee of the National Institute of Blood Transfusion gave ethical approval for this work (DC-2016-2872). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. 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 All data produced in the present work are contained in the manuscript