The interaction between ApoE4 carrier status and ACE inhibitor use on AD (Fig. 1) may explain the previously reported conflicting findings of the relationship between ACE inhibitors and the risk of developing AD dementia [19], e.g., some studies showed a beneficial effect [5, 6], but another showed no effect or a harmful effect depending on the subclasses of ACE inhibitors [5]. This evidence concerns the gene APOE and dementia.