To compare the effects of KU-60019 for different Cas9 species, we used a gRNA:target library with 12 pathogenic 1-bp deletion alleles causal to diseases, such as cystic fibrosis - a monogenic disease associated with the cystic fibrosis transmembrane conductance regulator (CFTR) gene - and familial adenomatous polyposis sites, for which 1-bp insertion editing with KKH-SaCas9, a smaller Cas9 orthologue shown to be amenable to in vivo gene editing27,28, should preferentially restore the pathogenic allele to wild-type genotype. The gene discussed is CFTR; the disease is cystic fibrosis.