Proline codon 209 (CCT) in exon 5 was changed to threonine (ACT) (p.P209T) using an sgRNA (targeting TTTGTTATCCCTTTTCTGAAGG) and an ssODN template with CRISPR/Cas9 technology. This mutation reduces binding of the encoded peptide to TCF3 and TCF12. (J:326199)