Three or four copies of a dicentric 17q isochromosome in an acute myeloproliferative disorder.

The majority of metaphases in the bone marrow of a male patient aged 72 with a rapidly evolving aleukemic erythremic myelosis had 48 chromosomes with three copies, or 49 chromosomes with four copies, of an i(17q), which was seen to be dicentric in C-banded and Giemsa-11-banded preparations. There was also loss of a chromosome No. 5 and the addition of a chromosome resembling a No. 22. The presence of multiple copies of the isochromosome is postulated to be related to the acuteness of the condition.