Why Do Humans Still Have a Gene That Increases the Risk of Alzheimer’s?

Jan 8, 2017

By Ed Yong

When the former nurse Jamie Tyrone learned that she carried two copies of a gene called ApoE4, she “lost hope and direction,” and her “days were filled with fear, anxiety and sadness.” It meant that as she got older, she would likely develop Alzheimer’s disease, as her father had done before her.

The apoliprotein E gene, or ApoE, comes in three forms—E2, E3, and E4. The last one is the problem. People who carry one copy have a three-fold higher risk of Alzheimer’s than those with none. And those with two copies, as Tyrone carries, have 8- to 12-fold higher risks. Between 51 and 68 percent of them will develop the disease by the time they are 85. The risk is so large that some people who get their genomes analyzed (including James Watson, a co-discoverer of the DNA double helix) deliberately decide to redact their ApoE4 sequence. They’d rather not know.

Even if ApoE4 carriers manage to dodge Alzheimer’s, they aren’t out of the woods. Compared to the general population, they tend to have higher cholesterol levels, a higher risk of heart disease, and a faster pace of mental decline during old age.


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3 comments on “Why Do Humans Still Have a Gene That Increases the Risk of Alzheimer’s?

  • Of course it can be a simpler explanation still, by the time most of us get Alzheimer’s you are long past the time when you are likely to be reproducing. if it doesn’t stop you from breeding then it’s going to surely get pasted to the next generation not matter how unpleasant.



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  • Reckless,
    I agree with your assessment. And, not only is it typically after reproductive age but can be very late in life. It also seems that there are perhaps some environmental risk factors at play.



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  • Reckless Monkey #1
    Jan 8, 2017 at 6:45 pm

    Of course it can be a simpler explanation still, by the time most of us get Alzheimer’s you are long past the time when you are likely to be reproducing.

    Not only that, but in the harsh, brutish, and short, nature of life in earlier times, most would not even live to reach modern expectations of old age.

    The disabilities of Alzheimer’s could actually help cull the elderly from primitive populations, reducing the demands for food on the food-chains, and promoting survival of the younger generations.



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