Britain loosens rules on screening human embryos

Advocates of the change say it will help parents treat desperately ill children. Opponents fear it could lead to creation of ''designer babies" for spare parts.

Suzi Leather, head of the fertility board, said the decision would affect few families. ''We're going to look at this on a case-by-case basis, and we believe this should be a treatment of last resort," she said. ''However, it will make a very great deal of difference to a small number of people. It will help save the lives of some much-loved children.

''This is a cautionary advance for medical treatment for an existing, very sick sibling. I do not believe this is playing God," she said.

Joe and Julie Fletcher, of County Down in Northern Ireland, toasted the decision with champagne. They hope to have a child whose stem cells will help their son Joshua, 2, who now must have frequent blood transfusions for a rare blood disease. ''It is great news," Joe Fletcher said.

Nuala Scarisbrick, a trustee of the antiabortion group Life, said that while the group sympathized with the parents of sick children, it would be better to find other treatments than to create babies for tissue transplants. ''It means that we are trying to create perfect people, and that is wrong," she said. ''It's not a healthy thing for a society to do."

She said choosing embryos based on tissue type could open the door to allowing them to be selected for attributes like gender or eye color.

Stem cells are found in human embryos, umbilical cords, and placentas. They develop into the various types of cells that make up the human body, making them useful for treatments for some diseases.

The British Medical Association said it welcomed the decision and did not believe selecting an embryo on the basis of tissue type meant a newborn would not be cherished.