Platelet electron microscopy, aggregometry, and BMw evaluation. Average number of dense granules per platelet in each patient tested, compared according to the type of variant (A). Normal cutoff for adults is 1.2 granules/platelet (dotted orange line). Bars indicate mean and 1 standard deviation. Percentage of patients with normal, delayed/decreased, or absent platelet aggregation (B) and adenosine triphosphate release (C) in response to various platelet agonists. Representative BM histology of FPDMM patients showing small megakaryocytes with hypolobation (D) or separated nuclear lobes (E). BM flow cytometry analysis quantified percentage of monocytes of all nucleated cells based on expression of CD14 and CD64 (F), eosinophils of all cells based on expression of CD45, CD16 and side light scatter (G), lymphocytes of all cells based on CD45, CD3, CD19, and CD56 (H), CD4:CD8 ratios of CD3⁺ T cells (I), and CD34⁺ cells of all nucleated cells (J). Mann Whitney statistical analysis compared BM of controls (n = 16) vs FPDMM adults without malignancy (n = 24) (blue dots). Three FPDMM adults diagnosed with a myeloid malignancy (1 CMML and 2 MDS) are indicated by red dots but were not included in the statistical analysis which sought to evaluate differences in baseline (nonmalignant) patients with FPDMMvs controls. Pediatric patients with FPDMM without a malignancy were separated in the analysis as healthy pediatric controls were not available for comparison. Black horizontal lines refer to median. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001. Flow cytometry shows normal CD10⁺ B-cell precursors in a healthy marrow (K), compared with an FPDMM marrow (L) showing absence of CD10⁺ B-cell precursors. AA, arachidonic acid; ADP, adenosine diphosphate; Avg, average.