In relation to the AβPP-independent iAβ production pathway, AβPP-derived iAβ plays an auxiliary role: just as the starter motor ignites the car engine (and remains redundant for the duration of the engine’s operation), so too does AβPP-derived iAβ, when accumulated over the T1 threshold, ignite the autonomous, self-sustaining AD Engine and is rendered marginal, if not redundant, afterwards. This evidence concerns the gene APP and Alzheimer disease.