In single and double KI rats total MAPT and 4RMAPT protein levels are unchanged over time; the expression of the 3RMAPT isoform decreases and the Alzheimer’s disease-relevant AT100 phosphorylation, which is absent at 14 weeks of age in wildtype, single and double KI rats increases with age (Additional file 4). This evidence concerns the gene MAPT and Alzheimer disease.