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Genome editing targets beta-thalassemia in human embryos

02 October 2017

By Dr Rachel Brown

Appeared in BioNews 920

A genome editing technique called 'base editing' has been used to correct the mutation causing the inherited blood disorder beta-thalassemia in human embryos.

Although all resulting embryos were mosaic, the researchers at Sun Yat-sen University, China say their study shows the technique could be used to correct genetic disorders caused by point mutations - a mistake in just one of the four bases of the genetic code.

'We are the first to demonstrate the feasibility of curing genetic disease in human embryos by base editor system,' said lead researcher Dr Junjiu Huang to the BBC.

Unlike the more common genome editing technology CRISPR/Cas9, base editing does not cleave DNA to make an edit, which could reduce the likelihood of off-target edits.

The study, published in Protein and Cell, follows earlier work by the same team who, in 2015, were the first to use CRISPR/Cas9 on human embryos - also in an attempt to correct the beta-thalassemia mutation (see BioNews 799).

The researchers took nuclei from skin cells taken from a patient with the disorder, and inserted them into empty donor eggs, creating human embryos carrying the mutation. They then scanned the DNA of the embryos for the point mutation, which was a guanine base in the place of an adenine, and changed it back using an enzyme.

If used clinically, the team suggest the technique could one day prevent beta-thalassemia being passed onto future generations, or even be used to treat patients. However, the resulting embryos in the current study were mosaic, with about 20 percent of cells successfully corrected, and in some cases the technique introduced other mutations instead of fixing them.

'It really isn't a rival to CRISPR/Cas9. It is a modified version with different attributes,' explained Dr Seth Shipman, a geneticist at Harvard Medical School, to online news site Gizmodo.

The edited embryos were not intended for implantation, a scenario which remains illegal in many countries, including the UK.

Professor David Liu – who was not involved in this study - developed the base editing technique at Harvard University last year. Speaking to the BBC, he explained that 'about two-thirds of known human genetic variants associated with disease are point mutations. So base editing has the potential to directly correct, or reproduce for research purposes, many pathogenic [mutations]'.

Professor Darren Griffin, a geneticist at the University of Kent, said that 'while this is undoubtedly a highly significant advance, it is important not to get carried away about its widespread utility if put into clinical practice. An embryo would still need to be diagnosed as abnormal, then the base editor applied, then re-diagnosed to make sure that it had worked. This would be an involved procedure that would be very expensive.' 

Professor Robin-Lovell-Badge at the Francis Crick Institute in London, told the BBC that this approach is unlikely to be used clinically anytime soon, adding that 'there would need to be far more debate, covering the ethics, and how these approaches should be regulated'.

'And in many countries, including China, there needs to be more robust mechanisms established for regulation, oversight, and long-term follow-up,' he said.

The latest developments in genome editing and embryo research will be discussed at the session 'What Next for Genome Editing? Politics and the Public', at the Progress Educational Trust's upcoming public conference 'Crossing Frontiers: Moving the Boundaries of Human Reproduction'.

The conference is taking place in London on Friday 8 December 2017. Full details - including sessions, speakers and how to book your place - can be found here.


30 October 2017 - by Dr Rachel Huddart 
A new molecular tool to change individual letters in an RNA sequence may open up new possibilities for gene therapy...
30 October 2017 - by Julianna Photopoulos 
Scientists have developed the genome editing technique known as 'base editing' to turn adenine-thymine base pairs back to guanine-cytosine...

25 September 2017 - by Paul Waldron 
UK scientists have successfully edited the genome of human embryos to study the role of a gene key to the earliest stages of development...
07 August 2017 - by Charlotte Spicer 
Scientists have published their study confirming they are the first to correct a disease-causing mutation in human embryos using genome editing...
13 March 2017 - by Dr Katie Howe 
Chinese scientists have successfully used genome editing to correct mutations in viable human embryos for the first time...
27 April 2015 - by Ayala Ochert 
Chinese scientists report the first-ever genetic modification of human embryos using the CRISPR/Cas9 gene-editing technique, confirming rumours that these highly controversial experiments were underway...

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Published by the Progress Educational Trust


Public Conference
8 December 2017

Speakers include

Professor Azim Surani

Professor Magdalena Zernicka-Goetz

Professor Robin Lovell-Badge

Sally Cheshire

Professor Guido Pennings

Katherine Littler

Professor Allan Pacey

Dr Sue Avery

Professor Richard Anderson

Dr Elizabeth Garner

Dr Andy Greenfield

Dr Anna Smajdor

Dr Henry Malter

Vivienne Parry

Dr Helen O'Neill

Dr César Palacios-González

Philippa Taylor

Fiona Fox

Sarah Norcross

Sandy Starr


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