The myeloproliferative reaction in a child with Down syndrome: cytological and chromosomal evidence for a transient leukemia.

Infants with Down syndrome occasionally develop marked myeloproliferative reactions (MPR) indistinguishable from acute myelocytic leukemia but which spontaneously regress. Most authors have attributed MPR to immature or defective control on bone marrow development. In this report serial cytomorphologic and chromosomal findings in the bone marrow and peripheral blood of a child with the MPR suggests that MPR may be due to a spontaneously regressing clone of malignant cells. At the height of the myeloproliferative response, chromosomal studies demonstrated a clone of blast-like cells with a 21-22 translocation consistent with Down Syndrome and an X-8 translocation which was present only in the initial peripheral blood analysis harvested at 24 hours but was not present in the 72 hours samples. This X-8 translocation was not demonstrated in bone marrow or peripheral blood samples obtained at random times throughout the one year followup. During this period there was complete resolution of the MPR. In addition the chromosomes from one cell demonstrated several double minutes at the time of the MPR. Double minutes have previously been reported only in malignant diseases, especially tumors of neural origin and leukemia. These findings raise questions about the benign origin of the MPR and support the idea the MPR may be the result of a spontaneously regressing clone of malignant cells.