APP and Alzheimer disease: Thus, the product of the first, chimeric, phase of human AβPP mRNA amplification, namely C99, apparently drives AD pathology, whereas the product of the second, iPCR, phase of AβPP mRNA amplification, namely AβPP (which cannot be processed proteolytically under the neuronal ISR conditions), potentially facilitates the viability and functionality of the disease-affected neurons.