PSEN1 and Alzheimer disease: Familial AD is a hereditary form of AD caused by mutations in certain genes; notably, a mutation due to a polymorphism on chromosome 19 forms ApoE4 lipoprotein, which is inefficient at removing amyloid beta (Aβ) plaques from the brain’s cortical regions, thereby escalating AD risk, and presenilin 1 and 2 genes, responsible for the catalytic subunit of γ-secretase transcription, which have been reviewed previously [8,9,10].