As an example, the 5xFAD mouse model, which expresses human APP and PSEN1 transgenes with a total of five AD-linked mutations— the Swedish (K670N/M671L), Florida (I716V), and London (V717I) mutations in APP, and the M146L and L286V mutations in PSEN1, is significantly influenced by genetic background in the strain, with different strains presenting pathological features on considerably different time scales 130. Here, PSEN1 is linked to Alzheimer disease.