Changes in the ratio of 3R and 4R tau do not appear to affect total tau expression significantly, suggesting that factors that alter exon 10 splicing may also contribute to other human neurodegenerative disorders, such as Pick's disease (3R inclusions) and progressive supranuclear palsy or corticobasal degeneration (4R inclusions). Here, MAPT is linked to corticobasal degeneration disorder.