apoe4 blocking neurogeneration?

[hairyfairy]

Iv`e read that one of the reasons that apoe4 causes alzheimers is that apoe4 blocks regeneration of nerve cells in the brain. If so, why would this be? surely there`s no evolutionary advantage to this. Is there a way to overcome this disadvantage and promote neurogeneration despite having the apoe4 gene?

[NF52]

Iv`e read that one of the reasons that apoe4 causes alzheimers is that apoe4 blocks regeneration of nerve cells in the brain. If so, why would this be? surely there`s no evolutionary advantage to this. Is there a way to overcome this disadvantage and promote neurogeneration despite having the apoe4 gene?

That's one of many $64,000 questions with ApoE 4 ( as the old expression was, when $ 64,000 was a fortune!) As several evolutionary biologists and science writers have noted, "evolution" is likely to give preference to people who can survive long enough to have biological offspring and raise them to adulthood. Since ApoE 4 seems to help in societies with high levels of parasites (as in some isolated areas of S. America) it can be helpful in the survival of the young, even if it is not helpful in your late adulthood. Genes often affect multiple traits, which is known as pleiotropy. ApoE4 also seems to help with executive function skills (planning, organization, flexible thinking) which would also be helpful in surviving and helping raise children. And in the case of surviving melanoma, it could also confer an advantage in adulthood. Finally, it seems that ApoE 4 may have been helpful in surviving periods of famine, or at least extended calorie restriction.

So like every design, sometimes evolution creates a great design with a few downstream effects that only show up when people survive well into their 6th decade or later.

[sarahb12]

& cancer

[mike]

Why does there even need to be an ApoE4 advantage? E3 develops after man has acquired year round carbs in the middle east and then spreads from there. There is little migration back to subsahara Africa, so E4 rates are still high there. E4 is also high in places where it took modern man longest to get to and displace the existing older population, like Malaysia and Indonesia, and in the retreating glaciers in Northern Europe. E4s are lowest in the Middle East. Unlike new world tubers, the Africa yam must first be soaked in water to remove toxins and I'm betting this was man's first year round source of carbs. With the E3 allele and the ability to better utilize carbs, E3 modern man quickly overtakes early man.