The recurrent t(12;21)(p12;q22) translocation fuses two genes, TEL and AML1, that have previously been shown to be independently involved in myeloid malignant proliferations. A search for rearrangement of the TEL locus in the region known to be involved in t(12;21) was performed by Southern blotting in a panel of hematopoietic malignancies. The presence of a t(12;21) was confirmed by fluorescence in situ hybridization (FISH) and/or reverse transcriptase (RT)-polymerase chain reaction (PCR). We report that fusion of TEL to AML1 is specifically observed in at least 16% of the childhood B-lineage acute lymphoblastic leukemia (ALL) investigated, none of which had been previously identified as harboring t(12;21).

The translocation t(12;21)(p13;q22) is a frequent nonrandom rearrangement of B-cell lineage childhood acute lymphoblastic leukemia (ALL) which fuses the TEL and AML1 genes, normally localized to 12p13 and 21q22, respectively. The crucial chimeric gene, TEL-AML1, is transcribed from the der(21) and encodes the 336 NH2 aminoacics of TEL fused to the majority of the AML1 protein. The t(12;21) is very often associated with loss of the normal, untranslocated TEL allele. These various aspects are presented here.

Trisomy 14 as single karyotype aberration was detected in three patients, two with acute myeloblastic leukemia, AML-M2 type, and one with aplastic anemia. These new observations and the 28 previously reported cases confirm that trisomy 14 is a primary non random change, mostly confined to myeloid disorders.