ALBERT

Description: Abstract 5313 Introduction VWD 2B and PT-VWD are rare diseases, due to mutations inducing a gain of function respectively of von Willebrand factor (VWF) and of its platelet receptor, Glycoprotein (GP)1bα Case history We report here the case of a young girl, born with an extensive purpura and a severe thrombocytopenia: platelet count: 16G/L. There was no associated biological nor clinical abnormality. A high dose of 1g/kg of immunoglobulin G infused on day 1 was unsuccessful, and a HPA-1a (−) platelet concentrate infusion led to a partial and transient increase of the platelet count up to 60G/L. Thrombocytopenia then resolved spontaneously. Biological study showed no sign of materno-fetal allo- or auto-immunity, parents were not consanguineous. The diagnosis of type 2B VWD was performed when she was 5 months old: VWF:RCo 〈 13 IU/dl, VWF:Ag 60 IU/dl, positive ristocetin induced platelet aggregation (RIPA) at a low ristocetin concentration (0.5 mg/ml). RIPA mixing studies were unconclusive. The same biological abnormalities were found in the father, whereas the mother had normal hemostasis tests. The biological phenotype also included a study of the multimeric VWF structure, showing a marked decrease in percentage of VWF high and intermediate molecular multimers. Genetic analysis performed on VWF gene showed the heterozygous p.Pro1266Leu missense mutation in the VWF A1 domain. This mutation ( o ) is only slightly deleterious, and induces usually a mild disease, without thrombocytopenia, even in stress situations, with normal VWF multimeric distribution; therefore, it could not explain the biological phenotype severity in this family. GPIBA was then analysed, and a candidate point mutation p.Met239Ile was evidenced. This mutation had not been described yet, but p.Met255Val had already been found in diagnosed cases of PT-VWD. Conclusion This case underlines the utmost importance to characterize precisely neonatal thrombocytopenia mechanism. Furthermore, it points out the difficulties to performing PT-VWD diagnosis, which incidence is most probably underestimated. In our case, it was the systematic and extensive biological workout performed in this case of isolated neonatal thrombocytopenia, without any obvious cause, which led to the diagnosis of a PT-VWD, inducing a severe biological phenotype, associated with type 2B VWD characterized by a mild expression. It is, to our knowledge, the first case described to date of such a morbid association. Disclosures: No relevant conflicts of interest to declare.