The targeting construct inserted a floxed neomycin resistance cassette upstream of exon 12 and an additional loxP site downstream of exon 18. Exon 12 was inadvertently deleted in the original targeting construct. Cre-mediated recombination removed the floxed selection cassette. Deleted of exon 12 produces a frame shift and premature termination in exon 13. (J:253448)