In the human AD brain, levels of O-GlcNAcylation were found to be reduced by 50% compared to healthy controls, and this inversely correlated with tau hyperphosphorylation, supporting O-GlcNAcase (OGA) inhibition in disease and that an increase in O-GlcNAcylation could have therapeutic relevance [323]. Here, OGA is linked to Alzheimer disease.