Scientists have shown it may be possible to correct certain inherited diseases before conception using a technique that replaces unhealthy DNA in one human egg with disease-free genetic material from another.
The finding, reported today in the journal Nature, is the first to suggest gene therapy can be done before an egg is fertilized, sidestepping some ethical issues. The researchers, at Oregon Health and Science University in Portland, did their work using donated human eggs.
The experiment produced early cells, called blastocysts, as well as embryonic stem-cell lines, according to the report. While the procedure is legal in the laboratory, the resulting embryos can’t be implanted in women without U.S. regulatory approval, said Shoukhrat Mitalipov, the study’s lead author. His team is seeking clearance to take that next step, he said.
“It’s safe enough at this stage to proceed to clinical trials.” Mitalipov said during a conference call yesterday.
A previous study, published by Nature in 2010, by researchers at Newcastle University in northern England proved it was possible to transfer DNA from a fertilized human egg to another. This new study takes the process a step earlier, Mitalipov said.
“That technique is always associated with destruction of the donor embryo, and that ethically is problematic, especially in the U.S.,” he said.
The switch affected mitochondrial DNA, where mutations can lead to severe genetic diseases. Mitochondria are tiny structures found in every cell that produce the chemical fuel needed for life. Mutations in the mitochondrial DNA, which are passed on from the mother, can disrupt the functioning of these energy generators.
Scientists say the procedure could one day be used to prevent genetic disorders such as learning disabilities, heart disease and diabetes. Serious forms of mitochondrial disease affect as many as one in every 5,000 children, and no cures exist, according to the study.
Using a procedure called spindle transfer, researchers swapped DNA from 65 healthy human oocytes, or eggs, and then attempted to fertilize and grow them, compared to 33 control oocytes. Both groups had similar levels of fertilization, while half of the transferred oocytes displayed abnormal levels of development. The normally developing oocytes continued to advance as well as the unaltered embryos.
“Mitochondrial DNA has been implicated in wide range of diseases -- including Alzheimer, Parkinson’s and Huntington’s disease,” said Marco Conti, director of the Center for Reproductive Sciences at the University of California, San Francisco. “There are great opportunities here, it’s completely uncharted territory.”
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