British scientists have warned that an impending government decision that may ban stem cell research using animal eggs will jeopardize finding treatment and cures for degenerative diseases such as Alzheimer's and spinal muscular atrophy.

On Thursday, Britain's Human Fertilization and Embryology Authority is to announce whether such procedures should be permitted. Experts at the HFEA, the country's independent regulator of fertility and embryo research, will decide if this type of stem cell research falls within their jurisdiction, whether it is legal, and whether it should be allowed. The authority said it would not comment on the issue until a decision is made.

But the scientists involved say they have been informally told that the licenses are unlikely to be granted.

In a paper published last month by Britain's health department on proposed revisions to the Human Fertilization and Embryology act, which covers stem cell research, the government proposed outlawing the creation of hybrid embryos combining human and animal genetic material. Current restrictions on this practice, according to the report, are based on public concerns.

Still, Prime Minister Tony Blair insisted the government is not dead-set against the scientists' proposals. "If there's research that's going to help people, then we want to see it go forward," he said during a tour of a London hospital on Friday. He acknowledged there were difficult issues surrounding stem cells.

Several stem cell experts submitted applications for a license to create human stem cells using animal eggs. The process involves injecting an empty cow or rabbit egg with human DNA. That would produce an egg with human genetic material inside, with minute traces of animal genetic material.

After a burst of electricity, the egg would be tricked into dividing regularly, becoming a very early embryo from which stem cells could be extracted.

Removing the animal's nucleus ensures that it would not be a chimera, or human-animal hybrid. "When you remove the nucleus with its DNA, you remove the species identity of the egg," said Dr. Stephen Minger, director of the stem cell biology laboratory at King's College. The proportion of animal to human genes would be tiny, with 13 animal genes versus 30 000 human genes.

Minger and colleagues applied for licenses to do this kind of work to better understand degenerative diseases at the cellular level, with the aim of finding targets for new drug treatments. The embryos would not be allowed to develop for more than 14 days.

Using human eggs is not practical because transferring genetic material into a host egg is extremely inefficient. In addition, there are too few human eggs available. Scientists say they would be lucky to get two or three human eggs in one month. In contrast, they could easily get 200 cow eggs in a single day.

Experts fear the government may ban stem cell research involving animal eggs due to public misconceptions of Frankenstein-like experiments. Still, an IPSOS-MORI poll from 2003 found that seven out of 10 Britons asked supported embryo research.

"I support the research if it's for Alzheimer's," said Jane Gottfried, 46, who said her mother was a sufferer. "I think it's important we don't do anything to ban it."

The Church of England remains "profoundly uneasy" about the use of human genetic material, no matter how it is packaged, according to spokesman Steve Jenkins.

"It would be sad if the government chose to restrict this work," said Dr. Lyle Armstrong, a stem cell expert at Newcastle University who hopes to use animal-based human stem cells to understand how stem cells develop into different tissues in the body. "It's very important not only to Britain, but to humanity in general."

Britain has traditionally been a world leader in stem cell and cloning research. Similar research, creating human embryos from animal eggs, is currently under way in China and the United

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