Isochromosome 17 in a patient with a myeloproliferative disorders terminating in eosinophilic leukemia

A patient is described, who for more than two years had a myeloproliferative disorder which terminated in eosinophilic leukemia. Chromosome analysis revealed an isochromosome 17 in all metaphases of bone marrow cells. This abnormality has now been found in two out of six patients with eosinophilic leukemia investigated by banding techniques, and may therefore have etiologic importance. Chromosome analysis in the hypereosinophilic syndrome has practical value for differentiating malignant and non-malignant disease.