http://www.usatoday.com/story/tech/sciencefair/2012/10/24/mitochondrial-genetic-engineering/1654359/

A white blotch in the tube at right is DNA that has been removed from a human egg, center. The red dot is from a laser used in the procedure. Scientists have successfully transplanted DNA between human eggs and grown them into early embryos. (Photo: Oregon Health & Science University via AP)
Story HighlightsMethod aims to remove defective maternal genes from human eggs
Technique transplants a mother's chromosome into a defect-free donor egg
Findings are called 'encouraging'
7:02PM EDT October 24. 2012 - Biologists in Oregon report they've produced early-stage human embryos with genes from three parents, a new method that some day may keep babies from inheriting rare diseases carried by maternal genes.
The gene transplant researchers led by Masahito Tachibana of the Oregon Health & Science University in Beaverton, produced early-stage human embryos that contained healthy versions of "mitochondrial" DNA, which only comes from a mother. Defects in those genes can cause diseases involving muscle weakness, brain abnormalities and other ailments that occur in 1,000 to 4,000 births every year nationwide.
"This approach offers the potential for allowing women affected with mitochondrial genetic disorders to produce healthy children," says bioethicist Kevin Smith of the United Kingdom's Abertay University, who was not part of the research. The study researchers do not intend to produce children with the engineered embryos and called for further safety study of the technique.
This egg gene therapy diagram explains steps in a proposed fertility clinic treatment to avoid maternal gene diseases in children.(Photo: Mitalipov lab/OSHU)
Mitochondrial genes reside in the outer part of eggs, apart from the chromosome genes held in the center, or nucleus, of these cells. Chromosomal genes dictate most inherited traits, everything from the sex of a child to eye color to height. The mitochondrial genes in contrast hold the design of cellular powerhouses that translate nutrients into energy in biological processes.
In the Nature journal study, researchers inserted the chromosomal genes from women into 65 donor eggs and then fertilized them with sperm. The idea is that by taking the genetic nucleus out of an egg fertilized by two parents and implanting it into the egg of a mother with no history of such mitochondrial diseases, they can take mitochondrial genes hiding in the first mother's eggs out of the reproductive equation.
The researchers fertilized the eggs with sperm, which grew into embryos about 70% of the time, a normal rate. In just under half the cases, the eggs developed normally into early-stage human embryos. Stem cells harvested from these embryos solely contained mitochondrial DNA from the donor eggs, not from the original eggs from which the nucleus was withdrawn.
In effect, the embryos had three parents who donated genes to the embryos.
The study calls for more animal tests aimed toward federal approval of safety trials at fertility clinics to test the method. The intended beneficiaries of the technique are "families that already have children with mitochondrial diseases," says biologist Shoukhrat Mitalipov, a study co-author.
The news follows work done by English researchers in 2010 that introduced a separate approach to producing such "tri-parent" embryos. In that work, the researchers transplanted the central genes from an egg after fertilization, not before like the new study, into a donor egg. The news led to a British bioethics council report that this year called the procedure ethical if it could be shown to be safe. In the United States, however, groups such as the U.S. Conference of Catholic Bishops have criticized research such as that described in the new Nature study for involving the destruction of human embryos, which is barred by law from receiving federal research funding.
"Overall the findings are encouraging," says biologist Mary Herbert of the United Kingdom's Newcastle University, a leader on the team proposing the alternative approach to removing defective maternal genes from fertilized eggs. She expressed caution over the fact that only half of the engineered eggs successfully grew into embryos in the new study. "While, the researchers were able to grow some embryonic stem cell lines, the likelihood of pregnancy remains to be established."
"This is good, solid work; the real advance is to perform the procedure in human cells," says biologist Keith Latham of the Temple University School of Medicine in Philadelphia. However, he expressed caution about the chances of the Food and Drug Administration (FDA) approving clinical trials of the procedure. Latham headed a 2009 study showing some growth problems in mice produced using similar procedures. In the study, the Oregon Health & Science University researchers report that the technique has produced healthy 3-year-old monkeys.
An FDA spokesperson, Rita Chappelle, said any requests to perform human experiments to test the gene-swapping process "would be carefully evaluated" by the agency to see if federal approval is required.