Flow cytometric analysis of GPIIb-IIIa content in platelets from the proband, her father, mother, and sister. Washed platelets were incubated with anti-GPIIIa or anti-GPIIb MoAbs as described in Materials and Methods. Results are expressed as semilog plots of cell number versus fluorescence intensity. The upper panel shows the surface expression of GPIIb, using the MoAb M3, in platelets from the patient, from her parents and sister, and from a normal unrelated individual. The lower panel represents the surface expression of GPIIIa using the MoAb P37. The negative control represents the fluorescent signal of platelets treated only with the second antibody. The plot corresponding to the sister’s platelets overlaps with the control and, therefore, only one tracing was represented. For the sake of clarity, the original plots have been redrawn.