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‘Editing DNA’ to eliminate genetic conditions now a reality

Published time: April 22, 2014 15:04
Edited time: April 23, 2014 13:28
Christine Daniloff / MIT

Christine Daniloff / MIT

Scientists have employed a revolutionary genome-editing computer technique that accurately identifies one faulty genetic “letter” among billions and effortlessly repairs a genetic condition in animals, paving way for human trials.

The success, by MIT in Boston, is the latest achievement in the field of genome editing that has been catapulted into the spotlight through a technology that can pinpoint genetic faults in chromosomes and literally fix them by changing tiny segments.

To test their success, the Massachusetts Institute of Technology team targeted a single mutated bit in the genetic makeup of mice, which accounts for a crucial function of liver metabolism.


“What’s exciting about this approach is that we can actually correct a defective gene in a living adult animal,”
study leader Daniel Anderson said in a statement.

Anderson’s reasons for using the particular gene and condition in mice in the test are not accidental. In humans, the same condition is created by the same genetic mutation. It manifests itself in a buildup of a particular amino acid, whose accumulation inevitably leads to liver failure if not constantly kept at bay with drugs and dieting. This is why the team is excited to be able to offer the technique to humans within a few years.

“This work shows that CRISPR can be used successfully in adults, and also identifies several of the challenges that will need to be addressed moving forward to the development of human therapies,” said Charles Gersbach, assistant professor of biomedical engineering at Duke University, whose comments appear on the university’s statement.

CRISPR (clustered regularly interspaced palindromic repeats) relies on “cellular machinery” used by bacteria in defense against viruses. This machinery is copied and altered to create specific gene-editing complexes, which include the wonder enzyme Cas9. The enzyme works its way into the DNA and can be used to alter the molecule from the inside. The combination is attached to an RNA guide that takes the gene-editing complex to its target, telling Cas9 where to work its magic.


But that is not all. Included in this operation is also a template DNA strand. It replaces the one just damaged by the Cas9 and its material is used to create a new copy with replacement genetic material.

Markedly different from any other approach, the technique doesn’t cure the condition – it edits the actual DNA, as if the condition never existed in the first place, much like you alter a file and hit 'Save'.

The technique works by administering the developed CRISPR components by way of a high-powered syringe into a vein. And while new methods of delivery are necessary for human tests, Anderson believes it’s not unreasonable to expect their development in the near future.

For now, high-pressure injections are seen as too dangerous to be used on humans, but delivery remains the only real obstacle, aside from the work that will need to be done to identify other genes, mutations and conditions to target. Anderson’s team is currently working to develop new delivery methods.

Although the discovery of CRISPR sequences dates back to 1987, when it was first used to cure bacteria of viruses, its successes in higher animals and humans were only achieved in 2012-13, when scientists achieved a revolution by combining the resulting treatment system with Cas9 for the first time.

On April 17, the MIT’s Broad Institute announced that has been awarded the first-ever patent for working with the Crisp-Cas9 system.

The institute’s director, Eric Lander, sees the combination as “an extraordinary, powerful tool. The ability to edit a genome makes it possible to discover the biological mechanisms underlying human biology.”

The system’s advantage over other methods is in that it can also target several genes at the same time, working its way through tens of thousands of so-called 'guide' RNA sequences that lead them to the weapon to its DNA targets.

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