Serine codon 18 (AGC) was changed to isoleucine (ATC) (p.S18I) and serine codon 20 (AGC) to alanine (GCT) (p.S20A) using an sgRNA and an ssODN template with CRISPR/Cas9 technology. These mutations prevent phosphorylation of the highly conserved residues. (J:327336)