The TEL-AML1 translocation in two paediatric cases of acute lymphoblastic leukemia

Abstract

The TEL-AML1 translocation was detected in two paediatric cases of acute lymphoblastic leukemia. Case 14 was a three year old boy with a WBC of 5.0 x 109 /1 who was diagnosed with ALL-L1, while case 28was a five year old girl with a WBC of 22.1 x 109 /1 who was also diagnosed with ALL-L1 The karyotype of case 14 was 46XY[3] and that of case 28 was 46XX:[4]/46X:X, -5,add (9g),+mar[2]. Immunophenotyping of case 14 classified the case as CALLA-ALL with co-expression of the CD13/ CD33 myeloid antigens. RT-PCR on RNA from both cases generated a 464 hp fusion product which sequencing confirmed as the TEL gene joined to exon 2 of the AML1 gene. Case 28 also displayed a minor band of the 425 hp shorter fusion product in which the TEL gene is joined to exon 3 of the AML1 gene. A less intense band of the reciprocal AML1-TEL translocation was also detected in both cases. The presence of the fusion transcript was also confirmed by Fluorescence In Situ Hybridization (FISH). In case 14, FISH further revealed that a proportion of the cells with a TEL-AML1 fusion signal showed an associated loss of the non-translocated TEL gene.