Response of BFU-E erythroid progenitors to EPO. EPO dose–response curves derived from the homozygous VHL^P138L patient (▵), patient with heterozygous gain-of-function HIF2α^M535V mutation (□), and healthy controls (●; n = 8, T bars = SD). VHL^P138L-affected erythroid progenitors display hypersensitivity to low concentration of EPO (15–60 mU/mL). There was a relatively higher number of BFU-Es in comparison with healthy controls (number of colonies ± SD) in all analyzed EPO concentrations. The assays of VHL^P138L and HIF2α^M535V erythroid progenitors were not done concomitantly.