Park et al. (2019) used a CRISPR-Cas9 nanoparticle complex that effectively crossed the blood–brain barrier (BBB), entered neurons in adult mice, and produced high-frequency indels at target sites in the BACE1 gene, thereby reducing BACE1 expression and activity. This alleviated Aβ-related pathology and cognitive deficits in two AD mouse models (5XFAD and APP knock-in). Singer et al. (2005) used a lentiviral vector expressing siRNA targeting BACE1 to reduce BACE1 levels, thereby decreasing amyloid production as well as neurodegenerative and behavioral deficits in APP transgenic mice. The gene discussed is APP; the disease is Alzheimer disease.