Transient myeloproliferative disorder associated with trisomy 21, a wide range syndrome: report of two cases with trisomy 21 mosaicism.

Transient myeloproliferative disorder (TMD) is an uncommon syndrome strongly associated with abnormalities of chromosome 21. Blast transient proliferation appears most frequently at neonatal age and usually resolves spontaneously in two or three months. Two patients, a girl and a boy, with neonatal onset of TMD are reported. They both presented trisomy 21 mosaicism according to bone marrow cytogenetic analysis. Patient 1, on one end of the spectrum, showed a "classic" benign course with rapid resolution and favorable outcome. Patient 2, on the other hand, had two blast outbursts both followed by spontaneous remissions. He failed to thrive and never reached a good general condition, dying at 5 months of age from a respiratory infectious complication. The necropsy showed generalized extramedullary hemopoiesis without evidence of bone marrow blast infiltration or myelofibrosis. TMD has some clinical 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 trisomy 21 mosaicism may not have overt phenotypic stigmata, it is possible that many cases of TMD in these children may have a silent, non-detected course. We also conclude that a favorable outcome is not always to be expected in TMD.