BCL9 and acute lymphoblastic leukemia: However, one potential limitation to our work is that only the most common 7 subtypes with current clinical relevance are covered, and not all novel recurrent cytogenetic abnormalities of pediatric ALL were observed in our cases, especially some relatively rare but significant genetic alterations such as IKZF1 deletions, intrachromosomal amplification of chromosome 21 (iAMP21), low hypodiploidy (30–39 chromosomes), JAK2 mutations, fusion genes involving ZNF384, CRLF2 rearrangements, and the MEF2D-BCL9 fusion gene [18, 29–33].