The human W51 mutation which causes the duplication of amino acid 595 to 601 (REYEYDL; AGAGAATATGAATATGATCTC) was inserted in-frame into exon 14, replacing the endogenous single copy (RDYEYDL; AGGGACTATGAATATGACCTT). A loxP site flanked neomycin selection cassette was inserted into intron 15.