In neurodegenerative diseases such as Alzheimer's disease (AD), frontotemporal dementia with Parkinsonism on chromosome 17, Pick's disease, and others, intraneuronal aggregates of hyperphosphorylated tau are a hallmark pathological feature (4, 5), and their appearance correlates well with neuronal loss in these diseases (6–8). This evidence concerns the gene MAPT and neurodegenerative disease.