Conversely, decreased levels of total and/or phoshorylated tau have been found in CSF or in plasma (Sparks et al., 2012) of subjects with PD, Alzheimer’s disease (AD) and MCI compared to cognitively normal controls, with a significant positive correlation between changing levels of plasma tau and cognitive performance (Sparks et al., 2012). This evidence concerns the gene MAPT and early-onset autosomal dominant Alzheimer disease.