Pathology of cMTFM. Wright-Giemsa–stained peripheral blood smears from (A) a normal control, (B) patient 3-II-4 and (C) the clinically unaffected, genotypically G6b-mutated individual 1-III-9 (original magnification ×1000). Note the large, hypogranular platelets (arrow) and RBC anisocytosis in 3-II-4 and the rare giant platelet in 1-III-9 (arrow). Serial histologic sections of a bone marrow biopsies from (D,G,J,M) a normal control individual, (E,H,K,N) 3-II-4, and (F,I,L,O) 1-III-9 stained with (D-F) H&E (original magnification ×400), (G-I) Reticulin (original magnification ×600), (J-L) the megakaryocytic marker CD61 (original magnification ×400), and (M-O) G6b-B (original magnification ×400). Atypical megakaryocytes present in stellate clusters associated with increased reticulin staining are characteristic of cMTMF. Staining for G6b-B is entirely negative in the megakaryocytes and platelets from 3-II-4 and 1-III-9.