Primary myelofibrosis with myeloid metaplasia and cytogenetically abnormal clones in 2 children with Down's syndrome.

2 children with Down's syndrome showed severe anaemia, leucocytosis with blastic cells, thrombocytopenia and hepatosplenomegaly. Bone marrow aspirations were near-dry tap and marrow biopsy revealed primary myelofibrosis with myeloid metaplasia (MMM). Their course was short with a blood picture similar to that of leukaemia. They expired 2 months and 21/2 months after diagnosis, respectively. The cases were thought to represent an acute childhood variant of MMM. Cytogenetic study of circulating white cells by 24 h culture without phytophaemagglutinin stimulation revealed aneuploidy in both cases, the first case showing marked aneuploidy with a predominant karyotype of 50,XX,+8,+19,+19,+21 and the second case a mosaic of 47,XX,+G/48,XX+G,+G. The karyotype of phytohaemagglutinin stimulated lymphocytes was 47,XX,+G in both cases. These findings suggest that the abnormal karyotypes are those of circulating blastic cells which are abnormal clones of haematopoietic cells responsible for MMM. In Down's syndrome, MMM might not be so rare as reported.