[Complex translocation (8;15;21) (q22;p12;q22) in a child with AML-M2 showing de novo appearance of the short form of AML1-MTG8 chimeric mRNA during the course].

A 4-year-old boy admitted with exophthalmos was diagnosed as having acute myeloblastic leukemia with maturation (AML-M2). Chromosomal analysis (G-banding) showed t(8;15;21). Fluorescence in situ hybridization (FISH), reverse transcriptase-polymerase chain reaction (RT-PCR), spectral karyotyping (SKY), and nucleolar organizer region (NOR) staining suggested that this complex translocation might have resulted from stepwise translocation, namely an initial translocation between chromosomes 8 and 21, followed by a second translocation between der(21) and chromosome 15, rather than the other possibility of clockwise translocation. During chemotherapy, RT-PCR demonstrated the short form of AML1-MTG8 mRNA, in addition to chimeric mRNA of the usual length. Sequence analysis revealed that this shorter chimeric mRNA had resulted from deletion of a 250-bp sequence at the 5' end of MTG8. A literature search failed to reveal any similar cases of t(8;21) AML-M2 associated with this deletion of chimeric mRNA.