 TEL/AML1 gene fusion is the most frequent genetic lesion in pediatric acute lymphoblastic leukemia (ALL).     ///    Trisomy 21 is a recurrent secondary aberration in childhood acute lymphoblastic leukemia with TEL/AML1 gene fusion..     ///    "In a cohort of 50 RT-PCR-positive TEL/AML1 patients, karyotype examination by GTG banding and fluorescence in situ hybridization (FISH) allowed us to identify chromosome anomalies in addition to the already existing t(12;21). "