MAPT and tauopathy: A study evaluating the overall brain levels of tau protein and tau mRNA (RT and quantitative PCR) as well as 4R-tau and 3R-tau mRNA levels in the frontal cortex in various main tauopathies revealed decreased levels of tau mRNA with an increase in the 4R tau/3R tau mRNA ratio, but preserved tau protein expression in the frontal cortex in PSP brains [29].