APOE and early-onset autosomal dominant Alzheimer disease: The apolipoprotein-E (APOE) allele frequency, an established genetic risk factor for Alzheimer’s disease, within our cohort was 76% with ε3/3 allele, 19% with one ε4 allele and 1% having ε4/4 genotype, similar to expected numbers of a representative Caucasian population33.