PDC and anemia (phenotype): In the case of HIF, a combination of biochemical and physiological studies led to the proposal of an unexpectedly direct connection between the reaction catalysed by the PHDs (prolyl-hydroxylation of HIF-α, figure 1) and hypoxia sensing in animals [27,28], a finding that has stimulated the clinical development of PHD inhibitors for treatment of anaemia and other hypoxia-related diseases [1].