Heterogeneity of erythropoietin-dependent erythrocytosis: case report in a child and synopsis of primary erythrocytosis syndromes

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Abstract
To investigate the pathogenesis of polycythemia in a child with isolated, primary erythrocytosis, serum erythropoietin activity and in vitro erythroid progenitor cell responsiveness to erythropoietin were measured. Unstimulated erythropoietin activity was markedly elevated (1.8 IU/ml), and isovolemic phlebotomy induced a 4-fold increment above this level. In contrast to findings in an index case with this syndrome, normal erythroid colony growth patterns were present in patient marrow cultures. The primary mechanism of polycythemia in this individual is similar to that reported in the index case: an inappropriately elevated regulatory set point for erythropoietin production. Since an additional defect of progenitor cell hypersensitivity to erythropoietin is not always present, abnormalities at single or multiple sites of the erythropoietic regulatory axis may occur in primary erythropoietin-dependent erythrocytosis.