Congenital Acute Megakaryoblastic Leukaemia in Down's Syndrome.

The case of a newborn with Down's syndrome and congenital leukaemia is reported. The malignant white blood cells displayed the CD41 antigen (glycoprotein Ilb/IIIa) identified by monoclonal antibodies HP1-ld and FMC24 and the CD9/p24 antigen identified by monoclonal antibody FMC27. The number of cells in S-phase was 14%, as assessed by the incorporation of 5-bromo 2-deoxyuridine. No other chromosomal abnormalities were identified in addition to 47 XY + 21. The patient died 15 days after the diagnosis, due to Pneumocystis Carinii pneumonia. Post-mortem examination showed heavy leukaemic infiltration and cardiac abnormalities including inter-atrial septal defect and a patent Ductus arteriosus. This patient appears to be the first identified case of congenital leukaemia with megakaryocytic differentiation, although previous instances of transient abnormal myelopoiesis with megakaryocytic differentiation have been recorded in Down's syndrome.