Unusual inclusions occurring in the blasts of four patients with acute leukemia and Down's syndrome.

The blast cells from four patients with these patients revealed the inclusions to acute leukemia and Down’s syndrome be single membrane-bound structures conwere found to contain unusual inclusions taming electron-dense amorphous debris, which manifested similar morphologic membranous substance, and virus-like and cytochemical characteristics. Ultraparticles. structure studies of the blasts from one of I T is NOW WELL established that children with Down’s syndrome have an increased incidence of acute leukemia: the several studies supporting this conclusion have been reviewed by Rosner and Lee.’ These authors also found acute Iyn phoblastic leukemia to be the most common form of acute leukemia occurring in children with Down’s syndrome, dispelling the commonly held impression of the predominance of acute myeloblastic leukemia in mongoloid children. In addition to the increased incidence of acute leukemia in Down’s syndrome, there have been several reports of severe myeloid leukemoid reactions and “transient myeloid leukemia” occurring in newborn mongoloids.2’3 Blood and bone marrow specimens from seven patients with mongolism and acute leukemia have been studied in this laboratory in the last S yr. In three of these patients, two newborns and one 2-yr-old, the leukemic process was diagnosed as acute myelogenous leukemia. In the other four patients, ranging in age from 2 to 9 yr. the leukemic process was diagnosed as acute lymphoblastic leukemia. The blasts in the four patients diaghosed as acute lymphoblastic leukemia were characterized by prominent inclusions which have been noted only rarely in the leukemic cells of nonmongoloid individuals. The morphologic, ultrastructural, and cytocF emical studies of these inclusions constitute the basis of this report.