The targeting vector is designed to insert a loxP site flanked STOP cassette into intron 1. Exon 4 was modified to change alanine codon 146 to threonine (p.A146T), a mutation commonly found in patients with cancers of the gastrointestinal tract and blood. An FRT site flanked neomycin resistance gene cassette is placed into intron 4. Flp-mediated recombination removed the neo cassette. (J:276349)