CRISPR/Cas9 technology introduced a G to T mutation, changing the glycine at amino acid 542 to a stop codon (G542X), resulting in the most common missense mutation seen in cystic fibrosis. A silent T to C mutation was also inserted. qRT-PCR indicates reduced expression levels. Treating mice with the aminoglycoside G418, a suppressor of nonsense mutations, results in an increase in Cftr mRNA. (J:262928)