The first genetically engineered babies have been born in US experiments which cross frightening new ethical boundaries. Researchers claimed the children were healthy.
The changes are permanent and will be passed on when these babies have children in the future.
The announcement was met with dismay from many scientists. The experiments would have been illegal in the Republic, the UK and many other countries and the US government will not fund this type of embryo research.
Up to 30 genetically modified children have been born, 15 as a result of one experimental programme at the Institute for Reproductive Medicine and Science of St Barnabas, in New Jersey. The one-year-olds now carry genetic information from their fathers and mothers but also DNA from a second woman.
There have been attempts to transfer new genetic material into humans as a way to fight diseases such as cystic fibrosis. These changes are not permanent, however, and cannot be passed on to the next generation.
The new US experiments are profound, however, in that for the first time a child's "germline", or reproductive cells, also carries the changes. Descendants of these children will all now carry the extra DNA.
The children were born following a technique called "ooplasmic transfer", which involves taking what is known as mitochondrial DNA from a donor's egg and injecting it into the mother's egg before fertilisation. Genetic fingerprinting of two children has confirmed that they now carry genes from three and not just two people.
The scientists at St Barnabas wanted to supplement the mothers' defective mitochondrial DNA with healthy mitochondria taken from the donor. They describe their work in the journal, Human Reproduction. Altering the germline is new territory and many scientists have criticised the work. The New Jersey team claimed that the procedure helped overcome low fertility but this was dismissed by the infertility pioneer, Lord Winston of the Hammersmith Hospital in London.
"Regarding the treatment of the infertile, there is no evidence that this technique is worth doing," he told BBC news. "There is no evidence that this is a possible valuable treatment for infertility." The UK's Human Fertilisation and Embryology Authority described it as an unwelcome development and US and Canadian researchers have also criticised the work.
