Hypereosinophilia in a monosomy 7 myeloproliferative disorder in childhood

Hyperosinophilia in association with a monosomy 7 myeloproliferative disorder is described in an eight‐year‐old boy. Antileukemic treatment resulted in a decrease in the eosinophilia, but did not appear to affect the blast cell population or the presence of monosomy 7 cells in the bone marrow. These findings suggest that bone marrow karyotyping may be useful in differentiating pre‐malignant causes of eosinophilia from those with a more benign etiology.