TTR and Alzheimer disease: Alternatively, since it is clear that mice with two intact copies of the ttr gene still develop AD-like pathology, and there is considerable variation in the degree of pathology and behavioral abnormality seen from mouse to mouse in the same strain, it is difficult to get significant results without using relatively large numbers of animals of the same gender, precisely matched for age if one is trying to determine the pace of development of disease, rather than degree of pathology at the endpoint, which may be independent of the presence or absence of TTR.