PS1477 PLATELET DISFUNCTION IN NOONAN AND 22Q11.2 DELETION SYNDROMES IN CHILDHOOD

Background: An underlying thrombocytopathy seems to be the responsible for hemorrhagic symptoms in patients diagnosed with 22q11.2 deletion syndrome (22q11DS) and Noonan syndromes (NS). Whereas in 22q11DS it is explained by a defect in the membrane glycoprotein complex Ib‐V‐IX, the cause of thrombocytopathy in NS remains unclear. Aims: To study the incidence of thrombocytopathy in pediatric patients diagnosed with 22q11DS or NS assessing the utility of ISTH‐BAT questionnaire and laboratory techniques in this regard. Methods: Prospective study between March and December 2018 in children (2 to 18 year‐old) diagnosed with 22q11DS or NS. Hemorrhagic symptoms, total cell blood count, platelet indices, closure time and platelet aggregation were evaluated in all patients. Membrane glycoprotein expression was only performed in 22q11DS patients. Results: Among NS patients (n = 22), near 80% had an aggregation defect with adenosine diphosphate (ADP) and epinephrine without thrombocytopenia. A significant correlation ( p  < 0.05) between closure times and aggregation with arachidonic acid, epinephrine and ADP was found. This correlation was more evident in those patients with hemorrhagic symptoms. Five out 29 (17%) patients diagnosed with 22q11DS had thrombocytopenia. Impairment in ristocetin‐induced platelet aggregation was found. This defect was correlated with prolonged closure times. Moreover, a significant correlation between thrombocytopenia, closure times and hemorrhagic symptoms was demonstrated. Summary/Conclusion: This study shows in a cohort of patients with NS and 22q11DS a significant impairment of platelet aggregation which correlates with hemorrhagic symptoms and closure times. Thus, closures times might be useful as screening test to evaluate the bleeding risk in this group of patients.