Genetic influence on longevity estimated in twin study

After reanalysing decades of twin data, scientists now estimate that genetics plays a greater role in lifespan than was previously thought.

Scientists at the Weizmann Institute of Science, Israel, have compared the similarity between the lifespans of 'identical' (monozygotic) twins to the similarity between the lifespans of 'fraternal' (dizygotic) twins, and have concluded that lifespan has a heritability of roughly 50 percent.

'In our work, we tried to give a handle on the amount of variance between different people that can be attributed to genetics. Our study tried to partition the longevity factors into genetics and "everything else". The "everything else" is around 50 percent of the pile,' Ben Shenhar – a PhD student at the Weizmann Institute of Science, and first author of the study, published in Science – told Reuters.

Heritability measures how much of the difference between individuals within a population, with regard to a particular trait, can be explained by the inherited DNA of those individuals. If a trait tends to be more similar between identical twins than it is between fraternal twins, then this is taken as evidence that the trait is heritable. (The influence of de novo mutations in DNA, that owe nothing to the previous generation, is not included in the definition of heritability.)

Previous twin studies had estimated the heritability of longevity at six to 25 percent. In the present study, researchers analysed datasets from Sweden and Denmark, applying mathematical models that took account of the cutoff ages employed by previous researchers (the minimum age at which individuals must be alive to be included in a study). The present study also sought to account for a confounding factor in previous studies, namely extrinsic mortality, meaning deaths due to causes originating outside the human body (such as infectious diseases or accidents). The new analysis suggests that that heritability of lifespan is around 50 percent, similar to the heritability of many other complex human traits.

The researchers then used a more recent Swedish dataset, that included both twins raised together and twins raised apart, to confirm that extrinsic mortality can mask heritability. They found that as extrinsic mortality decreases, heritability increases. They also observed that genetic contributions to lifespan vary by cause and age – for example, dementia shows higher heritability than cancer at later stages in life.

'For many years, human lifespan was thought to be shaped almost entirely by non-genetic factors, which led to considerable scepticism about the role of genetics in ageing and about the feasibility of identifying genetic determinants of longevity.... By contrast, if heritability is high, as we have shown, this creates an incentive to search for gene variants that extend lifespan, in order to understand the biology of ageing and, potentially, to address it therapeutically,' said Shenhar.