Acute megakaryocytic leukaemia with acquired polysomy 21 and translocation t(1;21).

Cytogenetic study of a young child with acute megakaryocytic leukaemia (AML-M7) has shown a karyotype with 49–50 chromosomes with one and two acquired extra chromosomes 21. Fluorescence in situ hybridization detected a minor clone with translocation t(1;21) and loss of a part of chromosome band 1p36. Trisomy and polysomy 21 are not uncommon in AML-M7. A more systematic search for chromosome 21 rearrangements in AML-M7 using FISH techniques is proposed.