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A Great Dane may have a much shorter life than a Chihuahua, and scientists may have found a clue to why.

A new study links faster ageing in large dogs to changes in DNA that weaken the body's control over genetic material capable of copying itself and moving around the genome.

The research, involving 864 dogs enrolled in the Dog Ageing Project, offers a possible molecular explanation for why larger breeds tend to have shorter lifespans and face a greater risk of age-related diseases.

"Dogs provide an extraordinary model for understanding ageing because they show dramatic variation in lifespan within a single species," said senior author Noah Snyder-Mackler, a professor at Arizona State University.

HOW 'JUMPING GENES' SPEED UP AGEING

The team focused on stretches of genetic material that can copy themselves and insert those copies elsewhere in DNA, potentially causing damage. They are called jumping genes.

The body normally keeps them under control using chemical marks called DNA methylation. These help regulate genetic activity without changing the underlying DNA sequence.

However, as dogs grow older, some of these marks disappear, potentially allowing jumping genes to become more active.

Researchers found that more than 40% of regions associated with a type of jumping gene called LINE1 lost these chemical marks with age.

The decline was significantly faster in larger dogs.

On average, giant breeds lost about 35% more LINE1-related DNA methylation per year than small breeds. This appears to be a major factor shaping how quickly different dogs age, Snyder-Mackler said.

Co-author Blaise Mariner said the finding offered a molecular clue to the link between body size and lifespan in dogs.

CAN THIS APPLY TO HUMANS?

The study also found differences between male and female dogs in how these genetic regions were regulated.

LINE1 sequences on the X chromosome carried more chemical marks in males than in females.

"This was an unexpected result," said co-lead author Brianah McCoy, highlighting the complexity of biological ageing.

The findings could eventually help researchers understand ageing in humans.

Dogs share their environments with people and experience many similar age-related changes, making them useful subjects for research.

"Because they are companion animals, they can also be a powerful model with immediate relevance to human health," Snyder-Mackler said, adding that understanding jumping genes and the mechanisms that control them could one day help extend healthy lifespans.

However, the researchers cautioned that more work is needed to establish whether these DNA changes cause faster ageing or are a consequence of it.

The findings, unfortunately, do not yet offer a treatment to extend a dog's life.