Although the functional significance of the developmental switch in tau splicing remains unclear, its strong evolutionary conservation, and the fact that abnormalities in tau splicing have significant implications for axonal transport [44], amyloid processing [45] and the pathogenesis of human tauopathies [46–48] suggests that fetal isoform expression may play a necessary role in development while becoming toxic in the adult brain. Here, MAPT is linked to tauopathy.