PCSK9 and early-onset autosomal dominant Alzheimer disease: Although a previous study has shown that PCSK9 affects the expression of the β-site amyloid precursor protein-(APP-) cleaving enzyme 1 (BACE1), a membrane protease responsible for the production of toxic β-amyloid peptides that accumulate in neuritic plaques of Alzheimer's disease brains [126, 127], the analysis conducted in PCSK9 null and transgenic mice did not confirm these evidences [125].