Chromosome 1q+ in erythroid and granulocyte-monocyte precursors in a patient with essential thrombocythemia.

A 55-year-old man with essential thrombocythemia had multiplication of bands q21 to q32 of chromosome 1 in all studied mitoses from bone marrow, from unstimulated blood, and from erythroid and granulocyte-monocyte colonies grown in vitro. The multiplication was in the form of triplication in 16 out of 20 mitoses from the marrow and in 4 of 6 mitoses from the blood; the rest showed a duplication of this region. All 20 mitoses from erythroid and granulocyte-monocyte colonies showed the abnormality in the form of duplication. These findings indicate most probably a clonal evolution, the triplication having arisen in the clone with the duplication. This may be associated with early leukemic transformation. The detection of the 1q+ aberration in two different types of hematopoietic colonies indicates the involvement of multipotent stem cells in at least this patient with essential thrombocythemia.