Transient myeloproliferative disorder with 11q23 aberration in two neonates with Down syndrome.

Infants with Down syndrome may develop a transient myeloproliferative disorder (TMD) with the features of acute leukemia but resolving in a spontaneous remission. Chromosomal aberrations in addition to trisomy 21 have only rarely been described. In many cases of infant acute leukemia band q23 of chromosome 11 is involved in nonrandom translocations, often resulting in a rearrangement of the ALL-1 (MLL, HRX, HTRX 1) gene. Generally, this translocation carries a bad prognosis. We describe two newborn girls with Down syndrome and TMD in whom the constitutional trisomy 21 was combined with an acquired abnormality of chromosome 11. During the TMD the morphological and immunologic features were consistent with those of megakaryoblastic leukemia. The chromosome 11 abnormalities were del(ll)(q23), but rearrangements of the ALL-1 gene were not found. Our patients had remissions that occurred spontaneously or after a mild chemotherapy. The important finding is that additional chromosomal changes may occur during TMD in Down syndrome. The fact that the abnormality was in region 11q23 raises the question of whether the risk for developing leukemia is increased under these conditions.