Nishimura and colleagues reported that random mutagenesis generated a PS1 R278I mutation that results exclusively in the production of Aβ43 [15], and Saido and colleagues reported that mutant PS1 transgenic mice (R278I/APPsw) had elevated levels of Aβ43 and earlier formation of senile plaques in their brains [16]. This evidence concerns the gene PSEN1 and Senile plaques.