PSEN2 and Alzheimer disease: There are several known genetic mechanisms involved with AD that present potential targets for gene therapy including the Amyloid Precursor Protein (APP), Presenilin 1 (PS1) and Presenilin 2 (PS2) mutations which result in autosomal dominant inheritance of early onset AD and the apolipoprotein E4 (APOE4) allele, a genetic risk factor which increases genetic risk for late onset AD, also known as LOAD [8].