Very few people live to be 110 or older. Incredibly, many of these "supercentenarians" do virtually nothing to stay healthy or fit, leading scientists to speculate that certain genes are responsible. But recent analysis of the human genome suggests this is an oversimplification.

The genetic underpinnings of aging are far more complex than we thought. Based on what we know of supercentarians, or super-c's, genes must play a role in longevity. For example, there's a 19% lifetime incidence of cancer in centenarians compared to 49% in normal populations. Super-c's also have lower rates of cardiovascular disease and stroke.

And as the authors of the new study point out:

The genetic component of human lifespan based on twin studies has been estimated to be around 20–30 percent in the normal population, but higher in long-lived families. Furthermore, siblings, parents, and offspring of centenarians also live well beyond average. Lifestyle choices in terms of smoking, alcohol consumption, exercise, or diet does not appear to differ between centenarians and controls. Taken together, these findings provide ample evidence that extreme longevity has a genetic component.

So, in an effort to determine the genetic underpinnings of longevity, a Stanford University team led by Stuart Kim mapped the genomes of 17 supercentenarians (16 women and one man). Now, that may not sound like a large sample pool, but keep in mind that there are only 74 super-c's alive today, with 22 in the United States. These 17 samples were compared to those of 34 people aged 21 to 79.

Surprisingly, the researchers found no significant differences.

From this small sample size, we were unable to find rare protein-altering variants significantly associated with extreme longevity.

Nothing. Not even in IGF-1 — a protein-encoding gene that's known to slow the aging process.

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Bizarrely, they did discover that one super-c carried a gene variant that raises the risk of sudden death caused by irregular heart rhythms.

Subsequently, their analysis shows that

it is extremely unlikely that there is a single gene harboring rare protein-altering variants shared by all supercentenarians but no controls. It is not surprising that a highly complex trait such as longevity is not explained by a single Mendelian gene.

In other words, the genetic underpinnings of longevity are real — it's just that they're far richer and more complex than we anticipated. The aging process is likely the result of tens, or hundreds, or even thousands of closely intertwined genetic factors. And indeed, Kim believes these genetic differences will eventually be found.

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"We're continuing our search with more supercentenarians and more complex analyses," he says in a New Scientist article.

Read the entire scientific study at PLOS.

Image: Zurijeta/Shutterstock.