Ethical considerations aside, a major issue in cloning is whether or not clones are as healthy as normally conceived animals. The evidence so far has been mixed. Some cloned cows have received clean bills of health, but Dolly suffers from premature arthritis, and many cloned animals are obese. According to a report published online today by the journal Nature Genetics, mice cloned from somatic cells fare particularly poorly. Indeed, the study found that cloned mice had significantly shorter life spans than did their naturally born counterparts.
Atsuo Ogura of the National Institute for Infectious Diseases in Tokyo, Japan, and colleagues cloned a dozen male mice and compared their development with that of animals with the same genetic background born through either natural mating or in vitro fertilization (IVF). The first cloned mouse died after 311 days, and 10 passed away within 800 days. In contrast, only one out of seven naturally conceived mice died within 800 days. The IVF mice also lived longer on average than did the cloned animals.
The researchers determined that the clones suffered from severe pneumonia and liver failure, ailments that did not affect the control mice. They further found reduced antibody production in a second group of cloned mice, suggesting that the immune systems of the cloned animals are less adept at fighting off infections than are those of regular animals. But because two of the clones are still alive and may achieve normal life spans, the scientists caution that clone longevity may depend on a multitude of factors, including genetic background and the type of cell utilized as a donor.