Exon 6 was replaced with one in which nucleotide substitutions result in the introduction of an XbaI site at nucleotide 799 and the amino acid substitution of arginine for a stop codon at position 267 (X267R) recapitulating the familial British dementia (FBD) mutation and alanine for threonine at the 12th codon of exon 6 to humanize the sequence. A neo cassette inserted upstream of the modified exon 6 was removed by cre-mediated recombination.