Scientists have successfully edited a human embryo to completely remove a genetic mutation that causes deadly cardiac disease, which can trigger the heart to stop beating suddenly.

In the landmark trials, the US and South Korean team demonstrated how they can use CRISPR technology (a revolutionary tool used to edit DNA) to successfully free the embryo from a faulty piece of DNA introduced by one of the parents at conception.

This opens the door to potentially tackle thousands of inherited diseases, but this study focused specifically on hypertrophic cardiomyopathy, a condition that causes the heart’s muscular wall to thicken and affects one in every 500 people worldwide.

Caused by an error in a single gene, anyone carrying it has a 50% chance of passing it on to their future children, but editing the DNA removes this risk.

Dr Shoukhrat Mitalipov, who worked on the study, wrote in the ‘Nature’ journal: “Every generation on would carry this repair because we’ve removed the disease-causing gene variant from that family’s lineage.

“By using this technique, it’s possible to reduce the burden of this heritable disease on the family and eventually the human population.”

Taking sperm from a male donor who has hypertrophic cardiomyopathy, and an egg from a healthy woman, the team injected the CRISPR technology at the point of fertilisation to carry out the genetic repairs.

Although it was not 100% successful, the attempt worked in 72% of the 58 embryos – the biggest success rate anywhere in the world so far.

The embryos were then allowed to develop for five days, before the experiment was stopped; as no work of this kind with modified embryos is actually permitted to carry children to term, it is only for purposes of “better understanding” human development.

This includes in the UK where, according to the UK Human Fertilisation and Embryology Authority (HFEA) 2016 licensing, embryos must be destroyed within 14 days and cannot be implanted into a woman after being altered.

A spokesperson for HFEA said: “UK researchers can apply for a license to edit human embryos in research, but offering it as a treatment is currently illegal.”

This is the first time such a trial has taken place outside of China, where laws are more relaxed.

But all previous Chinese trials (the most recent was in 2015) have not been this successful, and have resulted in “mosaic” cells that are a tapestry of healthy and unhealthy cells, as well as parts of the genetic code being mutated.

The team said: “Mosaicism in gene-targeted human embryos is unacceptable in clinical applications.”