Acute lymphocytic and myelomonocytic leukemia associated with low platelet counts and a 21q- marker chromosome.

A terminal deletion of the long arm of one chromosome 21 at band q21 was found in two patients with acute leukemia and a low platelet count: one case of acute myelomonocytic leukemia and one case of acute lymphocytic leukemia. The segment deleted from chromosome 21 could not be found translocated to any other chromosome of the complement. The results indicate that the 21q- marker chromosome may be due to a true deletion and that the marker is no specific for primary thrombocythemia or other myeloproliferative disorders associated with thrombocytosis.