Circulating erythropoietin concentration associates with thromboembolism in sickle cell disease

Elevated erythropoietin (EPO) concentration associates with thrombotic risk in hypoxic conditions, hereditary erythrocytosis and treatment of anaemia with recombinant EPO. We evaluated sickle cell disease (SCD) patients from the University of Illinois at Chicago (UIC) and the Treatment of Pulmonary Hypertension and SCD with Sildenafil Therapy (Walk-PHaSST) study and found that higher serum EPO concentration associated with increased thromboembolic risk (combined odds ratio [OR] = 1.9, p = 0.0029, N = 557). Percent haemoglobin F and haemoglobin concentration strongly correlated with EPO concentration in SCD, and the haemoglobin F locus BCL11A affected EPO concentration through percent haemoglobin F. In peripheral blood mononuclear cells from 159 UIC patients, we identified an expression quantitative trait locus for EPOR encoding EPO receptor, in which the G allele of rs322139 associated with higher EPOR expression (β = 0.055, p = 2.0 × 10^-5). This G allele associated with lower EPO concentration in Walk-PHaSST (β = -0.23, p = 6.4 × 10^-5, N = 327) and UIC (β = -0.18, p = 0.017, N = 179), but not in normal populations. The G allele of rs322139 also associated with a trend to decreased thromboembolism (combined OR = 0.64, p = 0.054, N = 665). In summary, our study indicates that higher serum EPO concentration associates with thromboembolic risk in SCD and reveals a novel role of EPOR expression variation in modulating EPO concentration and, possibly, thromboembolic risk in this condition.