ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: The e13a2/e14a2 alternative transcripts (or b2a2/b3a2), resulting from the juxtaposition of BCR exon 13 or 14 with ABL1 exon 2, produce a 210 kDa protein, which is found in over 90% of CML patients.