MAPT and red-green color blindness: Diseases where tau has a direct and predominant causal effect on neurodegeneration are referred to as ‘primary tauopathies’, which include progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), Pick’s disease (PiD), aging-related Tau astrogliopathy (ARTAG), argyrophilic grain disease (AGD), primary age-related tauopathy (PART), and tangle-only dementia (TOD) (Table 1) [38,39].