However, the frequency of genetically defined leukaemia subtypes differs between children and adults: for example, TEL-AML+ leukaemias are almost exclusively present in children (22% of ALLs vs 2% in the adults) while BCR-ABL+ ALLs are much more frequent in adults (25% vs. 3% in children) [2,4,5]. Here, ABL1 is linked to leukemia.