Flow cytometric analysis of patients' and parents' platelets. Analysis was performed on whole blood with monoclonal antibodies against GPIbα (AP1) and GPIIbIIIa (AP2). Platelets were then analyzed for their binding to AP1. Filled area, mother and father; clear area, affected children. The results from analysis of an additional three normal volunteers are shown by thedashed lines overlapping the normal sample in the shaded area. There is no detectable GPIbα on the platelets of the two children, whereas the samples from the two parents are similar to those of the normal controls.