P1645: the severity of hemorrhagic syndrome and the weakening of the procoagulant activity of platelets in patients with wiskott-aldrich syndrome.

Background: Patients with Wiskott-Aldrich syndrome (WAS) have a reduced platelet count. Bleeding occurs in most patients and may result in death in 4–10%. The role of impaired procoagulant activity of platelets in WAS has not been studied enough. Aims: To study the role of the weakening of the platelets procoagulant activity in the development of hemorrhagic syndrome. Methods: We examined 25 patients with WAS, observed from June 2017 to January 2020. The median age was 2 years (9 months to 18 years). Patients complained of hemorrhagic manifestations. The severity of hemorrhagic syndrome was assessed using the Pediatric bleeding questionnaire (PBQ). Patients were divided into 2 subgroups depending on the severity of bleeding from 0 to 2 score (n=12) and 3-6 score (n=13). The control group (CG) included 42 healthy children, median age 10 years (from 2-17 years). Flow cytometry was used to determine the total number of platelets and the proportion of phosphatidylserine-positive (PS+) platelets at rest and after activation with a mixture of TRAP-6 and CRP. Statistical differences were analyzed using the Mann-Whitney test with a significance level of p<0.05. Results: The platelet count was lower in patient subgroups compared with CG (p<0.001), but did not differ between patient subgroups (p=1). In the subgroup of patients with bleeding from 0 to 2 points, the proportion of PS+ platelets at rest did not differ from CG (p=0.89), and after activation it was reduced (p<0.001). In the subgroup of patients with bleeding from 3 to 6 points, the proportion of PS+ platelets was lower compared with CG at rest (p=0.02) and after activation (p<0.001). After activation, the proportion of PS+ platelets in CG was ≥ 5%. In 10 (40%) patients, a decrease in platelet PS+ <5% correlated negatively with an increase in the severity of bleeding (corr.= -0.65, p=0.04). Summary/Conclusion: The weakening of the ability to generate procoagulant platelets in patients with Wiskott-Aldrich syndrome was related with an increase in the severity of hemorrhagic syndrome.