Cases have normally sized platelets but reduced numbers of α granules. (A) Representative May-Grünwald-Giemsa stained peripheral blood smear of patient E II.3. Platelets have a normal appearance (size and granularity) by light microscopy (magnification ×100). (B) Representative EM images for 2 unrelated healthy controls and 4 patients from pedigrees A, B, and E showing depletion of α granules. Marker is 1.5 μM for magnification x20 000. (C, D) The sizes and quantities of α granules per unit area of 20 platelets, quantified blinded to case/control status, in each of 5 cases and 7 controls. Linear mixed model with a fixed effect for case/control status, a random effect for pedigree (groupings in gray) and a random effect for sample. The P value under the null hypothesis that the fixed effect is equal to 0 is shown for each of the 2 responses.