Molly Nash suffered from Fanconi anemia, a genetic disorder that prevented her body from making bone marrow. Doctors say that without the transplant of her brother Adam's cells, the disease almost certainly would have killed the Englewood, Colo., girl by age 35, perhaps decades earlier.
Doctors now say her body, for the first time in years, is manufacturing neutrophils - white blood cells which fight bacteria - and platelets.
Molly jumped up and down with excitement Wednesday when she got the news, asking to go home, according to her parents, Jack and Lisa Nash, in an interview with CBS News Correspondent Russ Mitchell.
"Molly is doing great," said Mr. Nash. "We couldn't be happier."
Adam was born Aug. 29 after a process in which embryos created in a laboratory were genetically screened to make sure the embryo selected to be born would be free of the disease Molly has, and, be a compatible tissue donor.
This is the first known case in which parents created a baby genetically selected to help save a sibling's life.
Molly's quick recovery has elated her parents. Lisa Nash said her daughter loves to dance but hadn't felt like it for around six months, until now.
"The other night she and I were playing in her room, and a song came on and she got on the floor and started dancing," she said. "And that was when we knew that this was the right thing to have done."
Molly's expected to be released from the hospital within a week and will be closely monitored for the next two months. Her doctor, John Wagner of the University of Minnesota, says while Molly is not yet out of the woods, she now has a good chance at a normal life.
Wagner said he hopes Molly's success influences the debate over research using human embryos and helps to free up more funding.
"Embryo research could have real benefits to people," Wagner said. "This is just one example of it."
The topic is controversial because fertilized embryos that aren't implanted in a woman's uterus are kept frozen or allowed to die. Pope John Paul II is among those who have attacked the practice of discarding unused embryos.
Jeffrey Kahn, director of the University of Minnesota's Center for Bioethics, acknowledged that genetic screening might be misused but said the Nash case shows how it can be positive.
"A healthy child can also save the life of a sick sibling," he said. "And that's all to the good."
Mrs. Nash is not afraid to talk about the ethical questions raised by the conception and the transplant.
"Adam is probably the most wanted child on the face of this earth. We wanted a healthy child, a child that would not suffer the way Molly suffered for th past six years," says Mrs. Nash.
Referring to those who have criticized her family's decisions, Mrs. Nash says "They need to step back and put themselves in my shoes and say if it was their child, would they not go to the ends of the earth to save their child and ensure that future children aren't sick?"
In the Nash case, doctors fertilized 12 of Lisa Nash's eggs, tested 10 of the embryos, selected the one that became Adam, and froze the rest except for one embryo that tested positive for Fanconi anemia, Lisa Nash said.
The Nashes said they believe they did the right thing for their family and for other children with genetic diseases who might benefit from similar procedures, such as patients with sickle-cell anemia.
"Unless somebody has been where we have been, and watched Molly go through what she has gone through for the last six years, going through the chemotherapy, and the transplant, and all of that," says Mrs. Nash, "Unless somebody can say they have been where we have been, you don't know what you would decide."
If Molly is still doing well a year from now, the mother said, the Nashes will use the remaining embryos to try to have more children.
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