One known condition to affect cerebrovascular homeostasis is hyperhomocysteinemia (HHcy) and evidence suggests that HHcy may promote dementia by more than one mechanism, including cerebral microangiopathy, endothelial dysfunction, oxidative stress, neuronal damage, enhancement of beta-amyloid peptide-mediated vascular toxicity, neurotoxicity, and apoptosis [72,73,74,75,76]. This evidence concerns the gene APP and endothelial dysfunction.