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Four sheep cloned from the same animal as Dolly are all in good health, suggesting the original clone’s osteoarthritis may not have been a result of cloning.

Debbie, Denise, Dianna and Daisy were all cloned using cells from the same adult sheep as Dolly, who, 20 years ago, was the first mammal ever to be successfully cloned. The four “siblings” are now nine years old and all in good health for their age.

Dolly, however, was diagnosed with osteoarthritis around the age of five years, and was put down at the age of six when she developed a progressive lung disease. “One of the concerns in the early days was that cloned offspring were ageing prematurely,” said at the University of Nottingham.

This prompted his team to investigate ageing in other clones. They have monitored a flock of 13 cloned sheep, including Dolly’s siblings, measuring their blood pressure, insulin sensitivity, musculoskeletal health, and other traits. “We found that our clones, considering their age, were at the time of our research healthy.”

Cloning safety

The 13 sheep were compared to naturally bred sheep of the same age. While some of the clones showed signs of mild or moderate osteoarthritis, none were lame or required treatment for the condition, the researchers said.

Dolly and her siblings were created using a technique called somatic cell nuclear transfer (SCNT), in which an adult cell nucleus is inserted into an unfertilized donor egg whose own nucleus has been removed. To create Dolly, Ian Wilmut and his team at the Roslin Institute in Edinburgh, UK, had to apply the technique to 277 eggs. This resulted in only 29 embryos that were implanted into surrogate mothers, and from those, only Dolly was born.

Sinclair says that while SCNT is still not very efficient, several teams are working to improve the technique. “This could lead to the realistic prospect of using SCNT to generate stem cells for therapeutic purposes in humans,” says Sinclair. “However, if these biotechnologies are going to be used in future, we need to continue to test their safety.”

Journal reference: Nature Communications, DOI:

Read more: The clone that changed my life: 20 years after Dolly the sheep