TRANSIENT MYELOPROLIFERATIVE DISORDER IN A DOWNS NEONATE WITH REARRANGED T-CELL RECEPTOR BETA-GENE AND EVIDENCE OF IN-VIVO MATURATION DEMONSTRATED BY DUAL-COLOR FLOW CYTOMETRIC DNA-PLOIDY ANALYSIS

Neonates with Down's syndrome may develop a transient myeloproliferati ve disorder (TMPD) which on presentation is indistinguishable from acu te leukemia, with the difference manifest only on follow-up. The clinc al course is one of spontaneous remission in TMPD and relentless progr ession in leukemia. We describe a Down's neonate presenting with hyper leucocytosis and circulating blasts which were positive for CD34, myel oid (CD33), megakaryocytic (CD41,CD42b,CD61), and T-lineage (CD3,CD7), but not B-lineage, associated antigens. Clonal rearrangement of the T -cell receptor beta (TCR(beta)) gene was found, with the immunoglobuli n heavy chain gene in germline configuration, showing the disease to b e a clonal proliferation of a multipotential stem cell involving the m yeloid and T lineages. Dual-colour flow cytometric DNA ploidy analysis of CD41 positive blasts showed initially a predominant 2N population, but polyploidization to 6N and 8N cells was found on follow-up, conco mitant with a progressive decrease in circulating blasts, suggesting m aturation of the abnormal clone and a provisional diagnosis of TMPD. T his was shown by the eventual resumption of normal haemopoiesis with t he disappearance of blasts and the clonally rearranged TCR(beta) gene.