CRISPR/cas9 endonuclease-mediated genome editing is used to create an cysteine to tryptophan substitution at position 133 (C133W, TGT to TGG) and a silent C to G mutation in codon 132 (T132T) in exon 5. The silent mutation eliminates the PAM site and prevents recutting with Cas9. (J:332542)