Proportions of JAK2 genotypes in BFU-Es from patients with JAK2-mutated PV and ET. Each vertical bar represents 1 patient, divided according to the proportion of wild-type, heterozygous, and homozygous-mutant colonies obtained, with the absolute colony numbers shown above (WT/Het/Hom). BFU-E colonies were grown under low erythropoietin conditions as indicated. (A) Colony genotypes for 30 patients with JAK2V617F-positive PV (total 2287 colonies; mean 76 colonies per patient). (B) Colony genotypes for 29 patients with JAK2V617F-positive ET (total 2277 colonies; mean 79 per patient). (C) Colony genotypes for 18 patients with JAK2 exon 12-mutated PV (total 1931 colonies; mean 107 per patient). (D) Example sequence traces for patients with patients with homozygous JAK2 exon 12 mutations in colonies. (E) Examples of patients grown on 2 occasions show reproducibility of genotype proportions in JAK2V617F-positive PV, JAK2V617F-positive ET, and JAK2 exon 12-mutated PV (1 and 2 represent independent experiments). In total, 16 patients (5 “heterozygous-only” JAK2V617F-positive PV patients, 4 JAK2V617F-positive PV patients with homozygous and heterozygous clones, 3 JAK2V617F-positive ET patients with small homozygous clones, and 4 JAK2 exon 12-mutated PV patients with homozygous clones) were assessed in this way (mean time between experiments, 13 months; range, 2-32 months) and showed reproducibility of proportions of heterozygous and homozygous-mutant colonies.