PB1304 - Evaluation of platelet abnormalities in children with 22q11.2 deletion syndrome in Chiang Mai University Hospital

Background: 22q11 deletion syndrome (22q11DS) is a common chromosomal microdeletion syndrome. The increased bleeding phenotypes and abnormal hemostatic tests including thrombocytopenia, platelet dysfunction and acquired von Willebrand syndrome (AVWS) have been reported in Western countries.

Aims: The objective of this study was to determine the association between patients with 22q11DS and bleeding phenotypes and abnormal hemostatic tests.

Methods: A cross-sectional study was performed all subjects aged > 1 year with diagnosis 22q11DS. The demographic data and bleeding phenotype by Thai pediatric bleeding assessment tool (BAT) were obtained from the interview and chart review. Subjected were tested for complete blood count (CBC), prothrombin time (PT)/international normalized ratio (INR) and activated partial thromboplastin time (APTT), vWF:Ag, vWF:Act, platelet function analyzer-200 (PFA-100) and platelet GP expression including GPIIB-IIIA, GPIb and GP IX-V detected by using flow cytometry.

Results: Total 25 subjects diagnosed with 22q11.2DS with median age of 5 year (range 1-32.6). Twenty-four subjects (96%) had underlying of congenital cardiac anomalies (Table 1). Thrombocytopenia was found only in 1 patient (4%). Eleven subjects (44%) had low vWF defined by lower vWF:Ag and/or vWF:GPIbM than 50%, however, there was no subject who had vWF:Ag lower than 50%. Eight out of 20 subjects (40%) who were tested for PFA-100 had prolonged closure time (CT) defined by prolonged CT for collagen/epinephrine more than 150 seconds (5/20) and/or prolonged CT for collagen/adenosine diphosphate (ADP) more than 120 seconds (5/20). The median (range) of maximum fluorescence index (MFI) of platelet GP expression for GPIIB-III, GPIb and GPIX detected by using flow cytometry were 60,799 (13,297-89,909), 10,737 (896-19,100) and 31,896 (11,720-50,289), respectively (Table 2). None of the abnormal hemostatic tests was correlated with bleeding issues.

Conclusion(s): Thrombocytopenia, prolonged CTs by PFA and AVWS could be found in patients with 22q11DS. However, those abnormal findings were not associated with bleeding in this cohort.