MAPT and early-onset autosomal dominant Alzheimer disease: 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).