U.S. scientists have corrected a genetic heart mutation in embryos using CRISPR

These days-old embryos had their DNA altered using the gene-editing technique CRISPR

These days-old embryos had their DNA altered using the gene-editing technique CRISPR

The team programmed a gene-editing tool, named CRISPR-Cas9, that acts like a pair of molecular scissors to find that mutation - a missing piece of genetic material.

Led by Hong Ma of Oregon Health and Science University, the researchers then used the gene-editing technology known as CRISPR in the embryos to try to correct the error, which causes catastrophic genetic heart disease in adults.

Dr Shoukhrat Mitalipov, from Oregon Health and Science University (OHSU) in Portland, said "Every generation on would carry this fix because we have removed the disease-causing gene variant from that family's lineage".

In fact, current legislation in the USA prohibits the implantation of edited embryos. "I was told at age 12 that I could die suddenly and that there was nothing anyone could do about it", she says. Before such scenarios can take place, more research is needed for this type of technique.

Not all the embryos were perfectly fixed, though: 16 showed erroneous fixes to their MYBPC3 gene. The defective gene causes hypertrophic cardiomyopathy, the most common cause of sudden cardiac arrest in young athletes.

In the latest study, the mutation was corrected by a route that scientists have not seen before, with the cell copying healthy DNA from the mother's egg instead of the template.

The fresh attention comes from research involving human embryos. The gene-editing tool has made altering life's code faster and cheaper than ever before.

Three previous attempts at using CRISPR to create a genetically modified human embryos were carried out in China but produced mixed results. Happily, they found no evidence of such "off-target editing".

According to the World Health Organization, there are more than 10,000 human diseases that result from mutations in just a single gene.

Though the scientists only edited out mutations that could cause diseases, it modified the nuclear DNA that sits right at the heart of the cell that also influences personal characteristics such as intelligence, height, facial appearance and eye colour.

In February, the National Academy of Sciences released a 261-page report that gave a cautious go-ahead to human gene-editing, endorsing the practice for purposes of curing disease and for basic research but determining that uses such as creating designer babies are unethical.

In the mean time, though, scientists still have a lot to work out. As Dibbens puts it: "The study advances our understanding of gene editing technologies and again highlights the need for discussions on what situations gene editing will be used in in the future". When that was done, 42 out of 58 edited embryos were found to be free of the hypertrophic cardiomyopathy mutation. Or scientists can try delivering the missing DNA in a fix package, like a computer's cut-and-paste program.

Will there be a day birth to babies free of genetic disease, such as in a science-fiction film? But the prospect of editing a child's DNA before they are born remains very controversial.

The researchers co-injected the affected donor's sperm together with the CRISPR editor. They were never meant for implantation inside a womb or to grow to become human babies.

Other strategies now exist for preventing genetic diseases in offspring. One of them simply stitches the severed strands of DNA back together, deleting or adding genetic "letters" at random in the process.

Today, people who carry certain genetic diseases can opt for IVF and have their embryos screened for harmful mutations.

Future work will continue to assess the safety and effectiveness of the procedure and efficacy of the technique with other mutations.

"We would like to explore a correction for cancer genes particularly BRCA, which is inherited the same way and a single copy can cause breast cancer", he says. "The technology is not there yet".

As detailed in the paper's research methods, the scientists adhered to strict ethical guidelines, and were monitored closely by committees of individuals including not just scientists and doctors, but also members of the general public. "For numerous traits that people want in their next generation, there's not a single underlying gene". "We have to draw a line and the regulatory agencies have to decide what is it that we have to treat and if it's something that's not disease".

Critics have raised concerns that modifying embryos creates unknown risks to children and would be a slippery slope toward genetically enhanced "designer babies." Under normal conditions, half of the man's children would inherit the gene, the disease and the risk for passing it on.

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