MAPT and Alzheimer disease: While brain‐derived PHFs in healthy neurons may be phosphorylated at 2–3 moles of phosphate per mole of tau, AD‐brain‐derived PHFs can contain an average of 5–9 phosphate groups per molecule of tau.[49] Phosphorylation at specific residues, such as Ser202,[50, 51] Thr231,[52] and Ser396/404,[53, 54] are commonly linked to disease.