MLLT1 and leukemia: Also circMLLT1 9:6230570–6274759:- (exons 2–4), expressed in mature populations, will not be generated from the KMT2A-MLLT1 derivative, since the breakpoints of t(11,19) leukemias either abolish the MLLT1 exons undergoing circularization or fall in the intron flanking the backspliced exon 2.