RAB1B expression in platelets from the patients with RUNX1 haplodeficiency and healthy control subjects. (A) Platelets RAB1B mRNA levels in the index (P1) patient and 5 normal subjects (N1-N5) by quantitative PCR. Shown are mRNA levels normalized to GAPDH. (B) Immunofluorescence studies of platelet RAB1B expression in the index patient P1 and a normal subject. Platelets were labeled with RAB1B polyclonal antibody, detected with fluorescein isothiocyanate (pseudocolored red)–conjugated secondary antibody, and imaged on a Nikon E1000 microscope. Corrected total cell immunofluorescence is shown ± SEM. (C) Platelet RAB1B mRNA in 2 siblings (P2 and P3) from a second family with RUNX1 mutation and 5 normal subjects (N1-N5). (D) Platelet RAB1B immunofluorescence in patient P2 and 2 normal subjects. Bar, 10 μm (scale also applies to panel B). Corrected total cellular fluorescence is shown ± SEM. The P values represent comparisons of the patient with each of the control subjects. (E) Platelet RAB1B by immunoblotting in 3 patients (P1-P3) and 5 healthy subjects (N1-N5). Also shown is the ratio of RAB1B to GAPDH.