δ-secretase (also known as Asparagine Endopeptidase (AEP) and Legumain) is a soluble, pH-controlled lysosomal cysteine protease, previously linked to AD due to its ability to proteolytically cleave Tau [59] and recently reported to participate in APP ectodomain processing [60]. The gene discussed is LGMN; the disease is Alzheimer disease.