A number of fusion genes have been identified by study of acquired chr
omosomal translocations. Their detailed characterization has provided
insights into mechanisms of leukaemogenesis and has enabled the develo
pment of molecular methods to assist in the diagnosis and monitoring o
f residual disease after treatment. The TEL-AML1 fusion gene is associ
ated with a cryptic t(12;21)(p12;q22) translocation, and is the common
est known genetic abnormality in childhood B-cell precursor acute lymp
hoblastic leukaemia (ALL), occurring in about 25% of cases. We have us
ed RT-PCR, followed by Southern blotting and direct sequencing, to est
ablish the incidence of TEL-AML1 rearrangement in 131 adults with acut
e leukaemia (101 with ALL and 30 with chronic myeloid leukaemia in bla
stic crisis). Three patients were positive for TEL-AML1 transcripts. A
ll three had common-ALL. All other patients were negative for TEL-AML1
. We conclude that the TEL-AML1 fusion gene is found in adult ALL, tho
ugh less commonly than in children.