Platelets from the patients with ITP with <30 × 103 platelets/μL had a lower capacity to be activated, as shown through the reduced binding of PAC1 to fibrinogen receptors (Figure 3A) and the diminished exposure of P-selectin and CD63, released, respectively, from alpha and dense granules (Figure 3B,C). This evidence concerns the gene CD63 and autoimmune thrombocytopenic purpura.