Elucidation of the hierarchy between iron overload and erythropoietic activity on Hamp expression is of practical importance, as several diseases such as β-thalassemias, myelodysplastic syndromes, X-linked sideroblastic anemia or congenital dyserythropoietic anemia are characterized both by increased EPO levels and iron overload. Here, EPO is linked to Tangier disease.