The world's most famous case of early onset arthritis in a non-human may never have existed. Dolly
the sheep, the first animal cloned from an adult cell, has long been
thought to have had osteoarthritis at an early age. This has been used
as evidence for the dangers of cloning. A re-examination of her skeleton
has thrown this claim into question.
Dolly's cloning in 1996 was among the biggest scientific stories of
the 1990s, opening up a great array of scientific and ethical debates.
In 2003, however, the happy pictures of Dolly gamboling in fields or
caring for her daughters were replaced with something darker. At the age
of 6 – very young for a sheep – Dolly was euthanized to save her from a
painful death from lung disease.
Fears that this indicated something fundamentally unhealthy about
cloning mammals were compounded by the reports she suffered from early
onset osteoporosis. One premature disease might be a misfortune, but two
looked like a warning. However, other cloned sheep, including some from
the same cell line as Dolly, have lived healthy and full sheepy lives,
leading Professor Kevin Sinclair, of the University of Nottingham, UK, to question if Dolly really was that sick.
In Scientific Reports,
Sinclair and colleagues describe X-raying the skeletons of Dolly and
her daughter Bonnie. For good measure, Sinclair and co-authors also
examined Megan and Morag, the first two mammals cloned from
differentiated cells, unlike the undifferentiated mammary cell from
which Dolly sprang. Bonnie and Megan both showed osteoarthritis in many
of their joints, but this is typical of sheep at 11 and 13, the ages
these two reached. Dolly, on the other hand, had no signs of arthritis
in the majority of her joints. Those joints that were arthritic were
judged by three independent veterinary orthopedic specialists to be
mildly to moderately affected.
Sinclair's suspicions were aroused by his previous work
finding little sign of early onset arthritis in 13 cloned sheep. “No
formal, comprehensive assessment of osteoarthritis in Dolly was ever
undertaken,” Sinclair said in a statement. “We therefore felt it necessary to set the record straight."
 |
| Professor David Gardiner setting up bones for radiography to assess if cloned sheep are vulnerable to arthritis. Nature |
There seems little doubt Dolly was lame in her left hind leg, but
this could have been caused by many things, not all of them genetic. The
belief she suffered unusually early arthritis appears to come from a
single mention in the abstract of a conference paper, something that
became accepted without investigation. None of Dolly's original
radiographic records were preserved, but luckily for Sinclair's team,
her skeleton is still in the National Museum of Scotland. And cloning,
at least for sheep, may be safer than we thought.
Postado por Hadson Bastos
Comentários
Postar um comentário