PSEN2 and familial Alzheimer disease: However, we did succeed in identifying two mutations (formed by the NHEJ pathway) that may prove useful in analysing the role of the human PSEN2 gene in familial Alzheimer’s disease; an in-frame mutation, T141_L142delinsMISLISV, and a frame-shift mutation, N140fs. While the CRISPR Cas9 system can produce off-target effects [54] these are unlikely to have influenced out results since use of this system in zebrafish requires outbreeding of fish that typically segregates away second-site mutations (other than those tightly linked to the target mutation site).