Study: Clones Have Hidden, Dangerous Flaws

July 5 -- Nearly 98 percent of attempts to clone animals have failed and those that do survive often appear abnormal and grossly enlarged. Now researchers say they have new evidence to explain why.

By tracing specific genes in cloned mice, Rudolph Jaenisch, a biologist at Whitehead Institute at the Massachusetts Institute of Technology and colleagues, found that while clones showed no clear flaws in their genetic make-up, the animals did reveal problems in expressing their seemingly normal genes.

The team traced this gene expression problem not to the cloning process itself, as scientists had suspected the problem might lie, but to the original stem cells that were used to help create the cloned mice.

"We found that embryonic stem cells are unstable — the state of their genes changes a lot," explains Jaenisch. "What was surprising was despite this genetic irregulation, still some embryos developed into pups. This means that those cloned animals that reach birth or beyond may appear normal, but our research shows they're not."

Sounding Caution

Scientists may have succeeded in cloning sheep, mice, cows, pigs and goats, but Jaenisch says this new research adds to mounting evidence that cloning remains a poorly understood science and one that is not ready to be undertaken with people.

Mark Westhusin, a cloning expert at Texas A&M University in College Station, Texas, points out that problems with genetic expression — the way information in genes is manifested in the body — are difficult to detect and this makes the practice of cloning even more dangerous.

"It's not gene mutation, it's gene expression," he says. "This is not something you can set up a test to prevent."

Ryuzo Yanagimachi, a professor of anatomy and reproductive biology at the University of Hawaii and co-author of the study appearing in this week's issue of Science, says "it is outrageous and irresponsible to try human cloning."

The work also casts some uncertainty on the field of stem cell research for fighting disease. In this field, scientists propose using embryonic stem cells to clone adult human cells and tissue, which then can replace diseased tissue of those suffering from heart disease, multiple sclerosis, Alzheimer's and other diseases.