A Genome Medicine study cautions that CRISPR-Cas9 gene editing can leave a hidden “mosaic” aftermath that standard screening approaches may miss. Researchers reported near-perfect long reads revealing heterogeneity left behind by gene editing events. The finding matters for preclinical and clinical interpretation because mosaicism can affect genotype-phenotype links, raise safety considerations, and complicate claims of uniform editing when only partial detection methods are used. The work reinforces the need for higher-resolution readouts when evaluating edited-cell populations, especially in therapeutic contexts.