Genetics

04 August 2017

Breakthrough: Doctors can now ‘edit’ genes in human embryos

A new technique can potentially be used to prevent transmission of genetic disease to future generations.

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In a first-ever experiment, geneticists have successfully modified a human embryo to remove a mutation that causes a life-threatening heart condition.

This is the first study to demonstrate that a gene-editing technique can be used in human embryos to convert mutant genes back to their normal version, the researchers said.

This new procedure tackled a genetic mutation in human embryos that causes hypertrophic cardiomyopathy, an inherited condition in which the heart muscle becomes abnormally thick.

The mutation was successfully repaired in 72% of 18 embryos that were created in a lab using sperm from a male donor who carries the hereditary heart condition, said team member Dr Paula Amato. She is an adjunct associate professor of obstetrics and gynaecology at Oregon Health & Science University (OHSU) in Portland.

Unlike other parts of the world in which cardiomyopathy is rare, heart muscle disease is endemic in Africa.

Impact on future generations

The procedure also might work in other genetic diseases caused when a person has one good copy and one mutated copy of a gene, Amato said. These include cystic fibrosis and cancers caused by mutated BRCA genes.

"This embryo gene correction method, if proven safe, can potentially be used to prevent transmission of genetic disease to future generations," Amato said.

But while the procedure is considered to be the first of its kind, human trials are not currently allowed in the United States.

genetic editing of mutation causing heart disease

A serious heart condition

Hereditary hypertrophic cardiomyopathy occurs in about one out of every 500 adults, and is passed along when a person winds up with one good copy and one mutated copy of a gene called MYBPC3, the researchers said.

There's a 50% chance that the children of a parent with the disease will inherit the genetic mutation for the disease, according to a Mayo Clinic estimate.

People with hypertrophic cardiomyopathy are at increased risk of heart failure and sudden heart death. The condition is the most common cause of sudden death in otherwise healthy young athletes, researchers said in background notes.

How the 'editing' is done

To repair the problem, the research team "broke" the mutated version of the MYPBC3 gene inside human embryos, using technology that allows scientists to snip a specific target sequence on a mutant gene.

Scientists discovered that when this occurs, a DNA repair process employed within human embryos activates to fix the broken gene, using the normal copy of the gene as a template.

The result: an embryo with two healthy copies of the gene that, if implanted in a woman and allowed to gestate, should result in a baby free from risk of hereditary cardiomyopathy. Further, any children descended from that baby should also be free from this genetic risk.

The researchers found that when they performed this procedure, all the cells in corrected embryos wound up containing two normal copies of the gene, Amato said. The new report was published in the journal Nature.

The next step

Researchers will next focus on testing the safety and improving the efficiency of the CRISPR-Cas9 process, possibly by using other genetic tools in combination with it, Mitalipov said. After that, they could proceed to human trials, in which the corrected embryos would be implanted with the goal of establishing pregnancy.

In the United States, the US Food and Drug Administration is prohibited from considering clinical trials related to germline genetic modification, Amato said. In addition, the US National Institutes of Health are not allowed to use federal funds to promote embryo research. It is possible that human trials could occur in another country with laws allowing such procedures, Mitalipov said.

In the area of stem cell research, South Africa allows the derivation of human embryonic stem cells from excess In vitro fertilization (IVF) embryos, and also allows for the creation of human embryos for research.