Abstract
Animal studies suggest that phosphorylation of microtubule-associated protein tau is a physiological way of destabilizing axons in the developing brain, promoting synaptic plasticity, while in the adult human brain tau phosphorylation is a specific sign of Alzheimer's disease. We here show, for the first time, that newborn human infants have extremely high levels of phosphorylated tau in their cerebrospinal fluid, and that these levels decrease during the first years of life. Tau phosphorylation in Alzheimer's disease may be a physiological response to Alzheimer-associated synaptotoxicity.