Removing a Genetic Alteration: A Look at Altering DNA Sequences

Removing a Genetic Alteration: A Look at Altering DNA Sequences

MIT Scientists Use CRISPR to Cure Rare Liver Disorder in Mice

Researchers at the Massachusetts Institute of Technology (MIT) have successfully utilized a novel gene-editing system to reverse disease symptoms in mice afflicted with a rare genetic liver disorder. The scientists' findings, detailed in the March 30 issue of Nature Biotechnology, mark the first evidence that this gene-editing technique, CRISPR, can potentially cure genetic disorders in living animals.

The study offers hope for treating a wide range of genetic disorders, including hemophilia, Huntington's disease, and others caused by a single mutated gene, according to the research team.

"We can actually correct a defective gene in a living adult animal," says Daniel Anderson, the Samuel A. Goldblith Associate Professor of Chemical Engineering at MIT and senior author of the paper.

The recent development of the CRISPR system capitalizes on cellular machinery bacteria use to defend themselves against viral infections. Researchers have replicated this system to create gene-editing complexes that include a DNA-cutting enzyme called Cas9 bound to a short RNA guide strand that targets a specific genome sequence, informing Cas9 where to make its cut.

Simultaneously, the researchers also deliver a DNA template strand. When the cell repairs the damage inflicted by Cas9, it copies from the template, introducing new genetic material into the genome. Genome editing of this kind could one day help treat diseases caused by single mutations, scientists conjecture.

Though other gene-editing systems based on DNA-slicing enzymes, or nucleases, have been developed, they can be pricey and difficult to assemble. By contrast, the CRISPR system is relatively simple to configure and customize, says Anderson.

For the current study, the researchers engineered three RNA guide strands that targeted various DNA sequences near the mutation causing Type I Tyrosinemia. This rare disorder, which affects about 1 in 100,000 people, prevents the body from breaking down the amino acid tyrosine, leading to liver failure.

The team administered RNA guide strands, the gene for Cas9, and a 199-nucleotide DNA template that included the correct sequence of the mutated FAH gene to adult mice with the defective FAH enzyme. As a result, the correct gene was inserted in approximately one of every 250 hepatocytes, or liver cells, over a 30-day period. These healthy cells multiplied and eventually replaced diseased liver cells, making up about one-third of all hepatocytes. This reversal of the disease was sufficient for the mice to flourish without the NCTB drug.

"We can do a one-time treatment and totally reverse the condition," says Hao Yin, a postdoc at the Koch Institute and one of the lead authors of the study.

The research underlines CRISPR's ability to be used successfully in adults and pinpoints several challenges that will need to be addressed to develop human therapies. For example, the efficiency of gene editing will need to improve significantly for most diseases, and alternative delivery methods should be explored.

In a statement regarding the research, Charles Gersbach, an assistant professor of biomedical engineering at Duke University, said, "The authors note that the efficiency of gene editing will need to improve significantly to be relevant for most diseases and that other delivery methods need to be explored to extend the approach to humans." However, Gersbach added, "This work is an exciting first step to using modern gene-editing tools to correct the devastating genetic diseases for which there are currently no options for affected patients."

To administer the CRISPR components, the researchers employed a technique known as high-pressure injection, rapidly dispersing the material into a vein. Nonetheless, Anderson's lab is currently researching methods that may be safer and more efficient, including targeted nanoparticles.

In addition to Anderson and Yin, the study's co-authors include Institute Professor Phillip Sharp; Tyler Jacks, director of the Koch Institute; postdoc Sidi Chen; senior postdoc Roman Bogorad; Eric Benedetti and Markus Grompe of the Oregon Stem Cell Center; and Victor Koteliansky of the Skolkovo Institute of Science and Technology.

The study was funded by the National Cancer Institute, the National Institutes of Health, and the Marie D. and Pierre Casimir-Lambert Fund.

1. The study detailed in the March 30 issue of Nature Biotechnology showcases the potential of CRISPR, a gene-editing technique, to cure genetic disorders in living animals, as demonstrated by MIT scientists in mice with a rare genetic liver disorder.
2. Researchers, led by Daniel Anderson of MIT, aim to treat a wide range of genetic disorders, such as hemophilia, Huntington's disease, and those caused by a single mutated gene, through the application of this gene-editing technology.
3. The CRISPR system, which replicates cellular machinery bacteria use to defend against viral infections, allows for the creation of gene-editing complexes that target specific genome sequences and introduce new genetic material.
4. Article on the progress of health-and-wellness research highlights challenges that must be overcome to develop human therapies using CRISPR, including the need for improved efficiency of gene editing and exploration of alternative delivery methods.
5. In the field of biotech and medical-conditions, the study serves as a promising initial step towards using modern gene-editing tools to correct devastating genetic diseases for which no current treatments exist.

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