MAPT and Alzheimer disease: The 3R and 4R isoforms of phosphorylated tau are well established [4] and are associated with various neurodegenerative conditions: the 3R tau is predominantly seen in Pick’s disease, 4R tau predominantly in progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD), and a mixture of 3R and 4R (3R/4R) tau in Alzheimer’s disease (AD).