Morphofunctional disorders of platelets in children with essential thrombocythemia and polycythemia vera

Introduction. Thrombosis and bleeding are frequent complications of essential thrombocythemia (ET) and polycythemia vera (PV). Platelet morphofunctional abnormalities in these disorders are poorly understood.

Aim: To study the morphofunctional characteristics of platelets in ET and PV.

Materials and methods. The study included 39 patients under 18 years of age with an established diagnosis of ET (n = 26) and PV (n = 13). The control group consisted of 40 healthy children. The manifestations of ischemic and hemorrhagic symptoms, hepato-/splenomegaly were evaluated. Platelets were studied using fl ow cytometry (FC) with activation by a mixture of thrombin and collagen analogues; the activity of the Willebrand factor was measured.

Results. Depending on the presence and type of driver mutation, all patients were divided into 3 groups. Group 1 included 16 patients with triple negative (TN) form of ET. Group 2 included 15 patients with JAK2 driver mutation and diagnoses of PV or ET. The third group included 8 patients with CALR driver mutation and a diagnosis of ET. The platelet count was higher in the TN group when compared to the JAK2 group (p = 0.005) and did not differ between the TN and CALR groups (p = 0.98). Hepatomegaly was observed in 36 % of patients, splenomegaly in 56 %. Symptoms of ischemia and/or bleeding were observed in 54 % of patients. Acquired von Willebrand disease syndrome developed in 64 % of patients. According to the results of FC, the size of non-activated platelets was reduced in all groups when compared to the control group (p ≤ 0.01). The reduction in platelet size upon activation was signifi cantly attenuated in JAK2 and CALR (p ≤ 0.0015). Platelet granularity was reduced in TN and CALR groups (p ≤ 0.01) when compared to the control. Morphological abnormalities of platelets, in the form of an increase in their granularity relative to cell size, were detected in 58 % of patients. The decrease in the amount of CD42b on the platelet membrane, due to Shedding and internalization, was signifi cantly attenuated in all patient groups (p ≤ 0.01). The externalization of CD61 on the platelet membrane surface upon activation was attenuated in all groups (p ≤ 0.02). In the JAK2 and CALR groups, the volume/number of platelet dense granules were signifi cantly reduced at rest (p ≤0.02), and upon activation, dense granule degranulation was attenuated (p < 0.001) when compared to the control. Conclusion. Common morphofunctional platelet abnormalities (reduced size, abnormalities in CD42b and CD61 expression) were identifi ed in children and adolescents with ET/PV, independent of the genetic cause.>< 0.001) when compared to the control.

Conclusion. Common morphofunctional platelet abnormalities (reduced size, abnormalities in CD42b and CD61 expression) were identifi ed in children and adolescents with ET/PV, independent of the genetic cause.

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