All six tau isoforms and tau tangles in the brain of AD patients are formed from both 3R and 4R isoforms with equal ratio, similar to healthy adults;[122,123,124] however, a higher ratio of 4R/3R was observed in PSP in comparison to AD patients and healthy adults.[124,125] Moreover, there have been several cases of PSP and frontotemporal lobar degeneration (FTLD) that had higher 4R tau/3R tau isoforms than FTDP-17 cases.[124]. Here, MAPT is linked to Alzheimer disease.