The protein tau has been implicated in the pathogenesis of a number of brain disorders, ranging from tauopathies such as progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and Alzheimer's disease (AD) to conditions not classically categorized as tauopathies, such as Parkinson's disease, Down syndrome, autism, and epilepsy. This evidence concerns the gene MAPT and early-onset autosomal dominant Alzheimer disease.