PSEN1 and familial Alzheimer disease: As a novel approach for treatment of early-onset familial Alzheimer’s disease, CRISPR-Cas9-mediated disruption of PSEN1 in human fibroblasts with the pathogenic PSEN1 M146L mutation can partially restore the disease-associated amyloid-β 42/40 increase, as well as reduce presenilin 1 levels.