JAK2 and polycythemia: In timed sacrifices at approximately 6 months of age, mice with combined mutations of IDH1R132H or Idh2R140Q and Jak2V617F showed polycythemia (mean hematocrit levels of 59% and 65%, respectively), leukocytosis (mean leukocyte counts of 23.78 K/μl and 16.22 K/μl, respectively; 1, A and E), and splenomegaly (spleen weights of 574.4 mg and 690.7 mg, respectively; Figure 1, B and F), which was similar to what we observed in the Jak2-mutant controls.