APP and early-onset autosomal dominant Alzheimer disease: Many key proteins involved in disease progression are N-glycosylated, such as amyloid precursor protein (APP) and β-site amyloid precursor protein-cleaving enzyme 1 (BACE-1) in Alzheimer's disease (AD) and alpha-fetoprotein (a clinical biomarker) in hepatocellular carcinoma [4, 5].