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RNA editing with CRISPR could treat genetic diseases

14 August 2017

By Emma Lamb and Annabel Slater

Appeared in BioNews 913

Scientists have repurposed CRISPR to target the repetitive RNA sequences responsible for several genetic diseases.

They suggest the approach could one day be used to treat diseases including Huntington's disease, hereditary amyotrophic lateral sclerosis (ALS) and myotonic dystrophy.

'We are really excited about this work because we not only defined a new potential therapeutic mechanism for CRISPR/Cas9, we demonstrated how it could be used to treat an entire class of conditions for which there are no successful treatment options,' said co-first author Dr David Nelles of the University of California, San Diego (UCSD).

Within cells, DNA is transcribed into RNA to produce proteins. Certain diseases are caused by mutations known as microsatellite repeat expansions – repetitive DNA sequences, which when transcribed cause a build up of toxic proteins known as RNA foci.

In a previous study published last year, the team adapted CRISPR/Cas9 to track RNA. They have now applied this technique, known as RCas9, to remove microsatellite repeat expansions from RNA.

The scientists showed RCas9 could remove 95 percent or more of RNA foci linked to myotonic dystrophy type 1 and type 2, one type of ALS, and Huntington's disease. It could also remove 95 percent of repeat RNA in cells taken from patients with myotonic dystrophy, and restore normal binding of MBNL1, a protein which binds RNA but is usually unable to do so in myotonic dystrophy type 1.

'There are more than 20 genetic diseases caused by microsatellite expansions in different places in the genome,' said Dr Ranjan Batra of UCSD, and co-first author. 'Our ability to program the RCas9 system to target different repeats, combined with low risk of off-target effects, is its major strength.'

As RNA is short-lived, any changes resulting from RNA-targeted genome editing would not be permanent. Speaking to KPBS, Dr Batra said this could be preferable in case of 'off-target effects'. Additionally, a viral delivery system for RCas9 could be effective for perhaps five to 10 years, according to senior author Professor Gene Yeo of UCSD.

The team also made a smaller version of Cas9 so that RCas9 could be delivered to patient's cells using a viral vector, which can be too small to hold Cas9. Professor Yeo said the next step would be to establish whether these viral vectors would elicit an immune response in vivo.

The study was published in Cell.

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