CSN2 and chronic myelogenous leukemia, BCR-ABL1 positive: The cas9 gene in the CML is a type II CRISPR-Cas subtype, usually composed of cas9, cas1, cas2, and cas4 (for type IIB) or csn2 (for type IIA) genes or only three cas genes (for type IIC), all located in a single transcriptional unit directly upstream of the CRISPR locus (Zhang et al., 2013; Makarova et al., 2015).