PHD2 loss causes severe polycythemia. (A) Hematologic parameters and (B) serum erythropoietin (Epo) levels in 10-week-old PHD2^+/+;Cre-ER (+/+) and PHD2 flox/flox;Cre-ER (F/F) mice after treatment with tamoxifen at E17.5 and at 3 weeks of age. (C) Real-time RT-PCR analysis for the indicated mRNAs from PHD2 conditional knockout (F/F) mice treated as in panels A and B. *P < .05; **P < .01. Error bars indicate 1 SD.