PB0268 - Desmopressin response may fail in children with congenital platelet function defects.

Background: Desmopressin can be used for treatment of congenital platelet function defects (PFDs), but little is published about the nature and duration of response in children with PFDs.

Aims: Evaluate desmopressin response in children with PFDs.

Methods: Observational study in children ≤18 years with PFDs that have received desmopressin (0,3mcg/kg). Good response was defined when Von Willebrand Factor (VWF) activity doubled from baseline 1-2 hours after infusion and Platelet Function Analyzer (PFA) was < 150sec, without co-existing low VWF. Descriptive statistics were used.

Results: Fourty nine children were included, mean age 12,2y (SD 4.48; range 4-18), 19 males (39%). A molecular defect was found in 30 (61%). Ten (20%) children had platelets < 100x10E9/L. Nine (18%) had Von Willebrand Factor activity (VWF) between 0,3-0,6 U/mL. Thirty two children responded good, but 16 did not meet both response criteria. Poor response was seen in 8/16 in whom VWF doubled, but PFA remained >150; In 3/8 without thrombocytopenia. In 1/16 PFA was normal, but VWF was < 1.5x the baseline (SOS1). In the remaining 7/16 none of the response criteria was met, 5/7 without thrombocytopenia. Non-responders had a molecular defect in genes involving platelet production or function or a syndromic disease: intestinal pseudo-obstruction (FLNA), Fechtner syndrome (MYH9) and DiGeorge syndrome (del(22q11)).

Conclusion(s): In 89% of children without a molecular defect desmopressin response was good (17/19). In contrast, non-responsiveness occurred in 14% of children, all with molecular defects without co-existing low VWF in all but one. The role of a continuous prolonged PFA without low platelets in PFDs remains unclear. More research is needed.