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Researchers 'edit' faulty DNA to cure genetic disease in mice

A team of MIT researchers has successfully cured a rare genetic liver disease in mice by "editing" the DNA to correct the mutated gene.

(Credit: little mouse, still sleeping image by Eddy Van 3000, CC BY-SA 2.0)

A team of MIT researchers has successfully cured a rare genetic liver disease in mice by "editing" the DNA to correct the mutated gene.

A new technique for editing DNA may one day be able to cure genetic diseases in humans, as demonstrated by a successful experiment performed by researchers at MIT. A team led by Samuel A. Goldblith associate professor of chemical engineering Daniel Anderson has managed to cure adult mice of a rare liver disease by correcting the genetic mutation that causes it.

The technique, called CRISPR (clustered regularly interspaced short palindromic repeats), is based on a technique bacteria use to fight viruses. When bacteria is infected by a virus, it contains short, repeating DNA sequences. These are then used by the bacteria to make RNA that binds the DNA to the virus. Then a second piece of RNA interacts with a protein called Cas9, which severs the virus DNA, thus inactivating the virus.

(Credit: Christine Daniloff/MIT)

In the CRISPR system, Cas9 is bound to a short RNA guide that is programmed to bind to a specific DNA sequence. This lets Cas9 know where to cut the DNA. At the same time, a new DNA template strand is delivered. When the cut DNA sequence repairs itself, it copies the template DNA — thus eradicating any mutations.

"What's exciting about this approach is that we can actually correct a defective gene in a living adult animal," Professor Anderson said.

The mice in this study had a genetic disease called Type 1 Tyrosinemia, which is an inability to break down the amino acid tyrosine. This amino acid accumulates in the system and can cause liver failure, and affects around one in 100,000 humans. Current treatments usually involve a low-protein diet and a drug that interrupts tyrosine production.

The researchers designed three guide RNA strands to target the DNA mutation that causes the disease. These were then inserted into one in every 250 hepatocyte liver cells, using a high-powered syringe injected into the veins of the mice, eventually delivering the RNA and template DNA to the liver. Over the following 30 days, the healthy cells began to grow, replacing around one third of the mutated cells — enough to cure the mice of Tyrosinemia.

Next, the researchers are working on a more targeted delivery method, and believe that the technique could be used to treat other single-mutation genetic diseases such haemophilia and Huntington's.

The full paper, "Genome editing with Cas9 in adult mice corrects a disease mutation and phenotype", can be found online in the journal Nature Biotechnology.