APOE and Alzheimer disease: Furthermore, animal studies have already provided evidence that stratifying disease by the largest risk factor for AD, age, dramatically impacts on treatment success (Kim et al. 2015), demonstrating the potential for predicting success in patients considering other common risk factors, such as APOE4 carrier status, for which there are humanised mouse models readily available (Knouff et al. 1999; Liu et al. 2017; Shi et al. 2017).