This secretase, an intramembrane aspartyl protease, is critically involved in Alzheimer’s disease (AD) via proteolysis of the amyloid precursor protein (APP), which generates the pathogenic and amyloid plaque-forming amyloid-β (Aβ)42 peptide (Steiner, 2008; Hass et al., 2009). The gene discussed is APP; the disease is early-onset autosomal dominant Alzheimer disease.