NF52 wrote: Our results suggest that solely APOE ε4-carriership does not influence brain function at a young age.
My personal experience and observation of known ε4 carriers early in life would agree with this statement.
One anecdote, my mother was a very bright woman. She died with dementia at 87. I have no idea if she is the parent I got my ε4 from. She got a degree in theoretical physics in 1948. Went on soon after graduation to supervise the military's early use of computers to track missiles (she wryly would comment - they gave the job to a woman because they expected it to fail and they could pay her half as much). When she was around 60, she went back to school and picked up a degree in computer science. She was always setting the curve, competing with students in their teens and early 20's. She would comment to me that her brain worked so much slower than when she was 19. I wasn't very sympathetic, saying, "but mom, you are setting the curve, how slow can you be?" Knowing what I know now about ε4's and glucose metabolism would validate her statement. Her ability to set the curve came not just from IQ (which may have been diminished), but her organization, focus, motivation, grit and so on.