Japanese scientists, from the National Institute of Infectious Diseases in Tokyo, have issued a report that says that cloned mice do not live as long as ordinary mice. The study, which appears in Nature Genetics, has cast further doubts on the safety of reproductive cloning in animals.
The researchers used seven naturally conceived mice and six mice conceived using a form of ICSI (intra-cytoplasmic sperm injection) with immature sperm. Each of the mice were then cloned. The 12 clones that resulted were compared with their genetic matches. After 800 days, 10 of the 12 cloned mice had died, while only three of the ordinary mice had. The cloned mice were autopsied to determine the causes of death and it was discovered that all of them had severe pneumonia, four had seriously damaged livers and two had cancerous tumours.
Dr Rudolf Jaenisch, a professor at the Whitehead Institute in Massachusetts, US, said that he was not surprised by the results of the study, adding 'it has exactly confirmed my strong belief and that of others. I think that most clones, if not all, have subtle defects'. Dr Davor Solter, from the Max Planck Institute in Germany agreed, noting that the study 'may serve as a deterrent, if one is needed, for some idiot who will start cloning people'.
Not all scientists share this view, however. Drs Tony Perry and Teruhiko Wakayama from Advanced Cell Technology (ACT), a biotechnology company in Massachusetts, said in an opinion piece in Nature Genetics that the study 'actually provides hope that cloning could be perfected' and that the results would give 'insight into where we should look for improvements' in cloning technology.