MAPT and Alzheimer disease: In addition, AD amyloid plaques are brittle and stiff: amyloid fibrils have high mechanical stiffness at 3.3 ± 0.4 GPa, as measured by Young’s modulus, making them more stiff than the surrounding brain tissue, and comparable in stiffness to spider silk [38]; and phosphorylated tau, as is present in NFTs in AD, is stiffer than non-phosphorylated tau [39].