APP and Alzheimer disease: Due to the steep rate of iAβ accumulation, however, the AACD phase in mutation carriers would be of substantially shorter duration than in wild-type counterparts; would relatively rapidly morph, upon crossing of the T1 threshold by AβPP-derived iAβ, into AD; and would, possibly, be unnoticeable or hard to diagnose as a separate condition (Figure 9, panels D/D’).