TRANSIENT MYELOPROLIFERATIVE DISORDER ASSOCIATED WITH TRISOMY-21, A WIDE-RANGE SYNDROME - REPORT OF 2 CASES WITH TRISOMY-21 MOSAICISM

Transient myeloproliferative disorder (TMD) is an uncommon syndrome st rongly associated with abnormalities of chromosome 21. Blast transient proliferation appears most frequently at neonatal age and usually res olves spontaneously in two or three months. Two patients, a girl and a boy, with neonatal onset of TMD are reported. They both presented tri somy 21 mosaicism according to bone marrow cytogenetic analysis. Patie nt 1, on one end of the spectrum, showed a ''classic'' benign course w ith rapid resolution and favorable outcome. Patient 2, on the other ha nd, had two blast outbursts both followed by spontaneous remissions. H e failed to thrive and never reached a good general condition, dying a t 5 months of age from a respiratory infectious complication. The necr opsy showed generalized extramedullary hemopoiesis without evidence of bone marrow blast infiltration or myelofibrosis. TMD has some clinica l and laboratory features that make it unique and distinguishable from true congenital leukemia with which it may be initially mistaken. It usually has a benign course followed by a favorable outcome. As trisom y 21 mosaicism may not have overt phenotypic stigmata, it is possible that many cases of TMD in these children may have a silent, non-detect ed course. We also conclude that a favorable outcome is not always to be expected in TMD.