FGFR4 and essential thrombocythemia: In our study, FGFR4, KLF2 gene expression was increased in PV, augmented by JAK2V617F mutant allele burden, while TGFBI level was increased in PV and ET patients. IFITM1 level was also increased in our PV and ET CD34+ cells, enhanced by JAK2V617F mutant allele burden (Supplemental Table 1).