In human bronchial epithelial cells, lung cancer cell line A549, and breast cancer cell line MDA-MB-231 cells, knockout of mdig gene by CRISPR-Cas9 gene-editing, resulted in a pronounced enrichment of histone H3 lysine9 trimethylation (H3K9me3) as well as H3K27me3 and H4K20me3 in ChIP-seq analysis, esp. The gene discussed is RIOX2; the disease is breast cancer.