Apolipoprotein E (APOE) genotype, especially APOE-ε4, represents a genetic marker for sporadic cerebral amyloid angiopathy (CAA), but its use as a risk factor for Alzheimer’s disease (AD) has also been described, whereas the APOE-ε2 biomarker is predominantly expressed in subjects with CAA-associated intracerebral haemorrhage. Here, APOE is linked to early-onset autosomal dominant Alzheimer disease.