Platelets from proband II-2 show impaired tyrosine phosphorylation after stimulation with convulxin (CVX) and reduced activation of the SFK SRC. Platelets were obtained from peripheral blood from proband II-2 and HCs. Lysates were prepared with resting platelets (time 0 seconds) and after stimulation with 100 ng/mL CVX for 60 and 300 seconds. Immunoblotting was performed with the 4G10 anti-phosphotyrosine antibody (P-Tyr), with an antibody recognizing SRC phosphorylated at Tyr419 (SRC activation tyrosine) and with an antibody recognizing SRC phosphorylated at Tyr530 (SRC inhibitory tyrosine). GAPDH was used as loading control. (A) Representative image of the immunoblotting experiments. (B) Densitometric analysis of tyrosine phosphorylation. The bands obtained with 3 separate experiments (mean ± SD) were analyzed. Change in tyrosine phosphorylation after stimulation with CVX for 60 and 300 seconds is expressed as the fold increase in the P-tyrosine/GAPDH ratio with respect to the resting condition. The proband showed a marked inhibition of the increase in tyrosine phosphorylation of all detectable proteins in response to CVX at both time points. (C) Densitometric analysis of SRC phosphorylation. The bands obtained in 3 separate experiments (means ± SD) were analyzed. SRC activation status is expressed as the SRC phospho-Tyr419/SRC phospho-Tyr530 ratio normalized to GAPDH. The proband showed significantly reduced activation of SRC under resting conditions and after activation with CVX. *P < .05, **P < .01 vs HCs, 2-tailed Student t test.