Our finding that certain clinically observed PHD2 mutations substantially alter ODD selectivity, that is, the erythrocytosis-associated P317R PHD2 (refs 24, 25) variant towards CODD, and the breast cancer-associated R396T PHD2 (ref. 27) variant towards NODD, implies that altered PHD2 selectivity may have pathological consequences. Here, EGLN1 is linked to breast carcinoma.