MAPT and Alzheimer disease: Mass spectrometric analysis, combined with sequencing achieved by Edman degradation and specific antibody reactivity, showed that almost 10 phosphorylation sites on tau can be detected in the normal brain (Ser46, Thr181, Ser199, Ser202, Thr231, Ser404, Ser412/Ser413/Thr414 and Ser416), and approximately 45 phosphorylation sites have been found in the AD brain [21,22].