We previously found that the relative concentration of the natively occurring sialylated Tyr O-glycosylated Aβ peptides were increased in CSF samples from AD patients relative to those of non-AD controls (n = 6 + 7), indicating that the presence of a Tyr-10 glycan might have an impact on the metabolic pathway of APP and thus become a candidate biomarker for AD8. This evidence concerns the gene APP and Alzheimer disease.