APOE and early-onset autosomal dominant Alzheimer disease: Additionally, as our results are based on cross-sectional amyloid data, we cannot exclude that parts of our findings could be explained by the recent suggestion that APOE genotype could be used as a surrogate measure of time with Aβ pathology,78 i.e. that Aβ-positive APOE-ɛ4 carriers have had Aβ pathology 10–15 years longer than Aβ-positive non-carriers, and that they therefore are further along in the neurodegenerative phase of Alzheimer’s disease.