Increased amyloid deposition in the brain has been linked to over-production of APP and Aβ in early onset familial AD cases which are caused by mutations in APP, PSEN1, and PSEN2, a phenotype that has been partially recapitulated in AD-like transgenic mice expressing mutant forms of APP and Aβ [17,18,19,20]. The gene discussed is PSEN2; the disease is Alzheimer disease.