APP and Alzheimer disease: The development of the APP/PSEN-1 double-transgenic mouse model, APP/PS1KI, for AD revealed, besides massive neuron loss in the hippocampus, many N-truncated AβX-42 variants including Aβ4–42 elucidated by two-dimensional Western blotting, which were subsequently verified by mass spectrometry (Casas et al., 2004).