Isochromosome 7q in Down syndrome.

Isochromosome 7q is not an uncommon chromosomal abnormality. It has been reported in association with Shwachman-Diamond syndrome, Wilms tumor, and hepatosplenic T-cell lymphoma. In other hematolymphoid malignancies, it occurs almost invariably as a secondary change. A notable example is its association with t(4;11)(q21;q23) in acute lymphoblastic leukemia. It has rarely been described in myelodysplastic syndrome and acute myeloid leukemia. We report the occurrence of i(7q) as the primary abnormality in a 2-year-old boy with Down syndrome and minimally differentiated acute myeloid leukemia.