Immunoprecipitation analysis. Biotin-labeled platelet proteins from a normal individual (lane 1) and the patient (lane 2) were immunoprecipitated with anti-GPIbα antibody (HPL7) and analyzed under reduced conditions. From the patient's platelets, it predominantly precipitated GPIbα and a small amount of GPIbβ and GPIX. Moreover, the amount of GPIbβ was less than GPIX.