In this study we have used CRISPR/Cas9-mediated HDR to correct the homozygous ASXL1 mutation found in the CML KBM5 cell line [13] and we have performed functional studies to determine whether the wild-type function of ASXL1 was restored following gene correction. The gene discussed is ASXL1; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.