Researchers have successfully transplanted the genetic material in the nucleus of a fertilized human egg into another fertilized egg, without carrying over mitochondria, the energy-producing structures of the cell. The technique could be used to prevent babies from inheriting diseases caused by mutations in the DNA of mitochondria, which are present in the cytoplasm of the egg. The British team carrying out the study used fertilized eggs donated by couples undergoing fertility treatment, and which were unsuitable for in vitro fertilization (IVF). At this early stage the sperm and egg nuclei, which contain most of the parental genes, have not yet fused. The researchers removed these nuclei and transferred them into another fertilized egg cell which had had its own nuclei removed.
As very little cytoplasm was transferred with the nuclei, the transfer left behind almost all the mitochondria from the donor egg. The researchers then grew the manipulated embryos for 6 to 8 days to determine whether they were able to continue development, and tested for the presence of donor mitochondrial DNA. Their work is published online by Nature today. Last year, researchers in the United States used a similar technique in monkeys; four embryos developed to term, and so far seem to be healthy and normal. “It's very exciting,” says David Thorburn, a geneticist who studies mitochondrial diseases at the Murdoch Childrens Research Institute in Melbourne. “It's a real shot in the arm for families that have had their children die from these various diseases.”