Exon 41 was replaced with a modified exon 41 with nucleotide substitutions (GGG to AGC) that results in the substitution of serine for glycine at position 2019 (G2019S). A floxed neomycin cassette was placed immediately downstream of exon 41 and was removed via cre-mediated recombination. Kinase activity is increased about 1.8-fold in heterozygotes and about 4-fold in homozygotes.