Platelet aggregation and integrin activation is markedly impaired in index cases with lifelong bleeding diathesis from 2 unrelated families. (A) Platelet aggregation in response to the indicated platelet agonists was evaluated in unadjusted PRP from index cases (P) and a healthy and unrelated control (C). (B) Platelets from index cases and healthy and unrelated controls (controls) (combined data from 3 participants) were stimulated under static conditions (30 minutes at room temperature) with agonist (5 and 25 μM ADP [ADP-5 and ADP-25], 25 μM PAR1p, 250 μM PAR4p, 2 and 10 μg/mL collagen-related peptide [CRP-2 and CRP-10], 2 μg/mL convulxin [Cvx], and 100 nM PMA) in the presence of fibrinogen-Alexa 488. The samples were evaluated by flow cytometry and the median fluorescence intensity (MFI) for fibrinogen-A488 binding is shown.