They have been extensively studied in various neurodegenerative disorders: the highest increase of T-tau was found in Creutzfeldt–Jakob disease (CJD) and Alzheimer’s disease (AD), a mild-to-moderate increase in frontotemporal (FTD) and Lewy body dementia (LBD), while normal levels were found in Parkinson’s disease (PD) and progressive supranuclear palsy (PSP). The gene discussed is MAPT; the disease is Parkinson disease.