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Update article on gene editing

Recent developments in gene editing that could change all our futures

Advances in gene editing are accelerating and opening up huge opportunities – and risks – for the human race.

The possibilities are immense. But what exactly is gene editing, how does it work and what’s it used for? We’ll answer those questions in this article, and also explore some implications (good and bad) of the technology.

How gene editing works

Gene editing is a technique that allows scientists to alter segments of DNA, such as faulty genes. A popular gene editor is CRISPR-Cas9, which was developed as recently as 2012 by two professors in California. It’s a fast and accurate tool that’s used by teams of scientists across the world.

CRISPR-Cas9 is based on how bacteria defend themselves against invading viruses. When under attack, the bacteria produce segments of DNA (called CRISPR arrays) that match the genetic sequence of the viruses. That allows the bacteria to ‘remember’ the viruses.

If the bacteria are attacked again, they use the CRISPR arrays to produce segments of RNA to target the viruses’ DNA. Once the RNA has locked on, the bacteria then use an enzyme called Cas9 to cut the DNA of the viruses and so disable them.

The CRISPR-Cas9 tool works in a similar way. Scientists create a segment of RNA (called Guide RNA) to bind onto the target sequence of DNA (the faulty gene). The Cas9 enzyme then cuts through both strands of the DNA, which inactivates the gene. The scientists can then insert a customised segment of ‘healthy’ DNA.

Recent breakthroughs

Pioneering advances in gene editing are coming thick and fast, with three major developments being reported in the last few weeks alone. Let’s look at them here, and discuss their significance.

1 – Groundbreaking treatment of muscular dystrophy in dogs

Scientists have successfully used gene editing to treat a fatal genetic disease in a large mammal, which is a significant step towards effective treatment in humans.

Duchenne muscular dystrophy (DMD) is a genetic disorder where the body can’t produce dystrophin, a protein that’s needed for muscle strength and function. In humans it mainly affects boys and young men, and leads to an early death from heart or respiratory failure. DMD also occurs in many dog breeds.

In this study – reported in Science journal – scientists used CRISPR-Cas9 to cut the faulty DNA in four dogs with the disease. This allowed the dogs to start producing dystrophin again, and restore it to their muscles. A 92% correction was seen in the heart, and 58% in the diaphragm.

Implications of correcting faulty genes in dogs
There’s still work to be done of course – but if gene editing were shown to be safe and effective in dogs, then the next step would be human trials. That could be a game changer for people with a genetic disease or disorder.

2 – Scientists cure lethal liver disease in prenatal mice

In this landmark study, mice with a genetic liver disease called hereditary tyrosinemia type 1 (HT1) were treated in the uterus before they were born.

The scientists used a version of CRISPR-Cas9 to edit DNA in the mice’s liver cells and cure the disease, according to a report in Nature Medicine. Humans can also have HT1, which can lead to liver failure or liver cancer. Untreated HT1 in humans is usually fatal by the age of 10.

Implications of altering genes in mice before birth
This proof-of-concept study is another step towards using gene editing to treat severe human diseases before birth. The technique could also be used to modify genes in human eggs and sperm (so-called germline gene editing). That, though, is highly controversial.

Yes, it could edit out genetic diseases and disorders, and stop them being passed down the generations. But it could also be used to alter genes for non-medical reasons. Gene editing could, for example, be used to enhance normal human traits such as height or intelligence.

It’s for this reason that human embryo and germline gene editing is currently illegal in many countries. But that’s about to change in Japan.

3 – Japan issues draft guidelines that allow gene editing in human embryos

An expert panel representing Japan’s health and science ministries has just issued draft guidelines that encourage this type of research. The guidelines restrict modifying the embryos for reproduction, although that’s not legally binding. If approved, implementation is likely to be in early 2019.

Japan would then join four other countries that permit gene editing research on human embryos – the UK, the US, China and Sweden

Implications of gene editing in human embryos
As mentioned above, the worry is that gene editing could be used to enhance ‘desirable’ human traits and create ‘designer babies’. That said, the importance of this research is recognised and is proceeding, although with extreme caution.

This approach is likely to be endorsed in the Second International Summit on Human Genome Editing, to be held next month in Hong Kong.

Summary

Gene editing using tools such as CRISPR-Cas9 is becoming more mainstream, and has been used recently to treat diseases in dogs and prenatal mice. The ambition is to use it in humans to treat and eradicate genetic diseases and disorders.

There is a risk that human gene editing could be used for non-medical reasons – to create ‘designer babies’ for example. But research is continuing with caution.

PRO

David Bain

Write On Target

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