Responses to hypoxia and to iron status are intact in VHL 598C>T homozygotes despite increased basal expression of hypoxia-regulated genes. (A) The relationship of serum erythropoietin concentration to hemoglobin concentration in 41 VHL 598C>T homozygotes and 70 unaffected participants, all of Chuvash ethnicity, is depicted. Regression lines and 95% confidence intervals are shown for each group. The dashed horizontal lines represent the lower (5 IU/L) and upper (35 IU/L) limits of the reference range for erythropoietin. The slope of the regression line is identical for each group (–0.007 log erythropoietin unit per 1 g/dL hemoglobin). (B) The relationship of serum transferrin receptor concentration to serum ferritin concentration in the same subjects is depicted. Regression lines and 95% confidence intervals are shown for each group. The dashed horizontal lines represent the lower (2.3 mg/L) and upper (8.9 mg/L) limits of the reference range for transferrin receptor. The slope of the regression line for the VHL 598C>T homozygotes (–0.154 log transferrin receptor unit per log ferritin unit) is almost identical to the slope for unaffected subjects (–0.158).