The APOE-ε4 allele, known for increasing the risk of Alzheimer’s and cardiovascular diseases, surprisingly exists in about 20% of humans.
Researchers embarked on a mission to uncover the reasons behind the survival of this seemingly harmful gene, and found it has a surprising advantage: increasing fertility in women.
Understanding APOE-ε4 through the Tsimane Community
The Tsimane community in Bolivia, with its hunter-farmer lifestyle, provides a snapshot into human life before the Industrial Revolution, making it an ideal study group.
Benjamin Trumble, an expert in evolutionary anthropology, along with a dedicated team, has worked closely with the Tsimane for over two decades.
Their main objective? To gain insights into human health and aging in a pre-industrialized setting.
Trumble’s perspective is clear: modern life has strayed far from how humans evolved. He stated, “We are now essentially operating outside of the manufacturer’s recommended warranty.”
The Study’s Findings
By analyzing data from 795 Tsimane women, researchers identified that those with the APOE-ε4 allele experienced increased fertility. Specifically, having one APOE-ε4 allele meant an average increase of 0.5 births.
Two copies of the allele? This led to an average of two more live births compared to women without it.
Trumble summarized their findings: women with the APOE-ε4 allele began reproducing earlier and had shorter intervals between births, which explained the increase in the number of offspring.
Balancing Benefits with Later-Life Risks
So, if the APOE-ε4 allele offers fertility advantages, why does it also increase the risk of Alzheimer’s and cardiovascular diseases? The answer might lie in what’s termed “selection’s shadow”.
Diseases developing after one’s reproductive years might not influence the survival of specific genes, as the genes have already been passed on to the next generation.
Additionally, other studies have linked the APOE-ε4 allele to positive effects, like better immune responses in children, leading to enhanced growth rates.
Trumble highlighted, “Children with the APOE-ε4 allele seem to have better immune function, so they spend less time sick and can grow faster.”
However, the detrimental effects of the allele, especially the increased risk for Alzheimer’s, primarily appear in Westernized countries.
Intriguingly, despite the Tsimane community having a 20% presence of the APOE-ε4 allele, they display the world’s lowest rates of Alzheimer’s.
Learning from the Tsimane
The evident disparity in the APOE-ε4 allele effects between Western nations and communities like the Tsimane suggests a need to reconsider our understanding of genetics.
Rather than simply associating one gene with one disease, there should be a broader exploration of how environmental and lifestyle factors can influence gene expressions and outcomes.
The diverse team behind the Tsimane Health and Life History Project, spanning anthropologists to Bolivian physicians, exemplifies the interdisciplinary approach required to deeply understand and address complex health and genetic challenges.
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The study was published in Science Advances.
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