Defective erythropoiesis in primary myelofibrosis associated with a chromosome 11 abnormality.

A case of primary myelofibrosis was identified with a previously unreported complex karyotype with two abnormal clones in addition to a proportion of normal cells: 46,XY,-2,-11, + der(2)t(2;11) (q24/31;q13), + mar and 45,XY,-2,-11, + der(2)t(2;11)(q24/31;q13), + mar, -17, del(7q). Study of circulating committed progenitors from this patient consistently showed (1) an absence of erythroid progenitors which is uncommon and (2) greatly increased granulocyte-monocyte progenitors (CFU-GM) which is generally observed in myelofibrosis. Further study showed that peripheral blood mononuclear cells co-cultured with irradiated normal bone marrow stroma generated increased numbers of CFU-GM compared with controls but failed to generate erythroid progenitors, providing evidence for an intrinsic defect in erythropoiesis. Only once previously has the absence of erythroid progenitors in primary myelofibrosis been studied in relation to cytogenetic abnormalities. This case also revealed a complex karyotype which, however, shared with our case a defect on chromosome 11. The identification of two cases of primary myelofibrosis which lack committed erythroid progenitor cells and which show in common a chromosomal defect on chromosome 11 point to the existence of genes on this chromosome which play a key role during erythropoiesis.