There has been so much speculation and multiple investigations into the role that genetics play in how we age. It wasn’t totally clear whether it played a greater role in health risks compared to age or if the reverse was the case.
This new study compared the effects of genetics, aging, and the environment on health risks. University of California, Berkley (berkeley) researchers found that genetic variation matters less in the expression of many genes as people get older, compared to both age and the environment.
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Genes are the basic unit of heredity that we get from our parents and through our evolutionary history. They determine who we are, our phenotypes (including height and weight), and our risks of health issues, such as heart disease.
“There’s been a huge amount of work done in human genetics to understand how genes are turned on and off by human genetic variation. Our project came about by asking, ‘How is that influenced by an individual’s age?’ And the first result we found was that your genetics usually matter less the older you get,” stated Peter Sudmant, an assistant professor of integrative biology at UC Berkley.
According to the researchers, the incidence of nearly all common diseases in humans increases with age. This suggests a need to give more attention to age when trying to identify the causes of disorders commonly seen in older people.
The results of this research were published in the journal Nature Communications.
Proof of Medawar’s hypothesis
The findings from this study were seemingly in agreement with a hypothesis by Brazilian-born British biologist Peter Medawar. According to the theory, evolution constrains more the genes that are turned on in people when they are young than when they are older.
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This is because gene expression is vital to ensure we survive long enough to reproduce. There is less evolutionary pressure on the expression of genes after a person reaches reproductive age.
Put differently, what this hypothesis suggests is that the role of DNA in health risks is greater in young people than in their older counterparts. It then means there should be less focus on genetic history when assessing what impacts how people age.
Going by the hypothesis, a large variation in how genes are expressed should be expected as people get older.
“We’re all aging in different ways,” explained Sudmant. “While young individuals are closer together in terms of gene expression patterns, older individuals are further apart. It’s like a drift through time as gene expression patterns become more and more erratic.”
How genes are expressed is central to multiple processes in the body. The degree of gene expression impacts many things from hormone levels to metabolism and enzyme mobilization for repairs.
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Probing the more important factor
The UC Berkeley researchers examined how genetics, aging, and the environment affect the expression of about 20,000 genes in humans. They used a special statistical model to assess these factors in 27 different tissues obtained from almost 1,000 persons.
The scientists found that the level of expression of many genes in the body varies widely among older people. This reduces the ability to predict health risks through genetic history or inherited DNA.
Sudmant noted that genetics played about the same role across all body tissues. However, aging was significantly different between the tissues and age played a bigger role in guiding gene expression.
Genetic makeup becomes less useful for predicting the risks of a person developing one of the common diseases after the age of 55, the researchers said. Its usefulness reduces for telling genes whose activity ramps up or goes down.
The team found that how genes are expressed even varied between identical twins as they get older. This means they could age differently and have different health risks.
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Sudmant and his fellow researchers found that Medawar’s hypothesis did not apply to all the tissues examined, however. There were higher expressions in older people of evolutionary key genes in five tissue types that are linked to most cancers. These tissues increase the risk of genetic mutations each time they replicate.
These findings could help researchers that are working to establish correlations between genetic variation and diseases of aging for drug targets.
References
Tissue-specific impacts of aging and genetics on gene expression patterns in humans
