Tau proteins are proteins which contain four Tau/MAP repeats. They promote microtubule assembly and stability, and might be involved in the establishment and maintenance of neuronal polarity. They are abundant in neurons of the central nervous system and are less common elsewhere, but are also expressed at very low levels in CNS astrocytes and oligodendrocytes. The tau proteins are the product of alternative splicing from a single gene that in humans is designated MAPT. When tau proteins are defective, and no longer stabilize microtubules properly, they can result in several neurodegenerative disorders such as Alzheimer's disease, Pick's disease, frontotemporal dementia, cortico-basal degeneration and progressive supranuclear palsy.