Some studies, evaluating the effects of the APOE genotype on AD clinical features in families carrying pathogenic mutations in APP, PSEN1 or PSEN2 genes, showed that the ε4 allele is associated to an earlier age of onset in the mutations’ carriers, while the carriers of the ε2 allele had a later onset [56,57,58]. Here, PSEN1 is linked to Alzheimer disease.