APOE and early-onset autosomal dominant Alzheimer disease: The emergence of an A−/T+ group in our study with certain ‘AD-like’ characteristics (i.e. poor recall and naming, entorhinal cortical thinning) and other dissimilar features (i.e. low APOE ε4 allele frequency) highlights the possibility that there may exist ‘non-traditional’ (i.e. initially Aβ negative) pathways to Alzheimer’s disease.