For this reason, mouse models of AD (including the APP.PS1 mice) are engineered to express various forms of the human APP. However, models of DS have been generated (e.g. the Ts65Dn line [84]) by producing animals with an additional copy of a portion of murine chromosome 16 that is syntenic with the DS critical region on the human chromosome 21 [85]. The gene discussed is PSEN1; the disease is Alzheimer disease.