CRISPR/cas9 endonuclease-mediated genome editing created a two base pair deletion in exon 5 of the Gtf2i gene. The mutation is located in the Williams syndrome critical region (WSCR) and is tightly linked to Gtf2ird1em2Jdd on Chromosome 5. The 2 bp deletion results in a premature stop codon in exon 5 and causes a nonsense-mediated decay. GTF2I protein expression is reduced by 100% in E13.5 brains from homozygous mice. (J:94077)