Scientists in Oregon have created embryos with genes from one man and two women, using a provocative technique that could someday be used to prevent babies from inheriting certain rare incurable diseases.
The researchers at Oregon Health & Sciences University said they are not using the embryos to produce children, and it is not clear when or even if this technique will be put to use. But it has already stirred a debate over its risks and ethics in Britain, where scientists did similar work a few years ago.
The British experiments, reported in 2008, led to headlines about the possibility someday of babies with three parents. But that's an overstatement. The DNA from the second woman amounts to less than 1 percent of the embryo's genes, and it isn't the sort that makes a child look like Mom or Dad. The procedure is simply a way of replacing some defective genes that sabotage the normal workings of cells.
The British government is asking for public comment on the technology before it decides whether to allow its use in the future. One concern it cites is whether such DNA alteration could be an early step down a slippery slope toward "designer babies" — ordering up, say, a petite, blue-eyed girl or tall, dark-haired boy.
Questions have also arisen about the safety of the technique, not only for the baby who results from the egg, but also for the child's descendants.
In June, an influential British bioethics group concluded that the technology would be ethical to use if proven safe and effective. An expert panel in Britain said in 2011 that there was no evidence the technology was unsafe but urged further study.
The genes they want to replace aren't the kind most people think of, which are found in the nucleus of cells and influence traits such as eye color and height. Rather, these genes reside outside the nucleus in energy-producing structures called mitochondria. These genes are passed along only by mothers, not fathers.
About 1 in every 5,000 children inherits a disease caused by defective mitochondrial genes. The defects can cause many rare diseases with a host of symptoms, including strokes, epilepsy, dementia, blindness, deafness, kidney failure and heart disease.