Dolly the sheep, the world's first cloned mammal, has developed arthritis, one of her creators said today.
Prof Ian Wilmut, who led the team which cloned Dolly in 1996, said her condition could have been caused by the cloning process and called for more research.
The emergence of arthritis in the world's most famous sheep led to a slump in shares for the company that developed the animal.
Prof Wilmut, of the Roslin Institute, Edinburgh, said: "Dolly has arthritis in her left hind leg, at the hip and the knee. We can't tell how it will develop but she is responding well to treatment with anti-inflammatory drugs".
Asked whether the condition was because Dolly was cloned, he said: "There is no way of knowing if this is down to cloning or whether it is a coincidence".
He also told BBC Radio 4's Todayprogramme: "We know already that there's an unusual incidence of death of cloned animals around the time of birth.
"What we need to go on studying is whether diseases like arthritis, which tend to be associated with older age, occur in a normal way or whether the incidence is changed. In every other way she is perfectly healthy and she has given birth to six healthy lambs".
Normal sheep of Dolly's age had been known to develop arthritis, he said.
Dolly made headlines in 1996 when she became the first mammal to be cloned using DNA taken from an adult cell from a ewe's udder.
PA