Monday, October 16, 2017

Huntington’s Disease: Gene Editing Shows Promise in Mouse Studies

This is another article snipped from the blog. Since Huntington’s and Kennedy’s Disease  both have extra repetitions of the CAG DNA, this is another advancement in treating and possibly curing these type diseases. As I mentioned in my previous post, the process is still experimental, but it is moving in the right direction. If you haven't read the previous update on gene editing, you can find it here.

To read the entire article, click on the title below.

Huntington’sDisease: Gene Editing Shows Promise in Mouse Studies

Posted on June 27, 2017 by Dr. Francis Collins

“…But years of basic science advances, combined with the promise of innovative gene editing systems such as CRISPR/Cas9, are providing renewed hope that we will someday be able to treat or even cure Huntington’s disease, along with many other inherited disorders.

My own lab was part of a collaboration of seven groups that identified the Huntington’s disease gene back in 1993. Huntington’s disease occurs when a person inherits from one parent a mutant copy of the huntingtin (HTT) gene that contains extra repetitions, or a “stutter,” of three letters (CAG) in DNA’s four-letter code. This stutter leads to production of a misfolded protein that is toxic to the brain’s neurons, triggering a degenerative process that, over time, leads to mood swings, slurred speech, uncontrolled movements, and, eventually, death. In a new study involving a mouse model of Huntington’s disease, researchers were able to stop the production of the abnormal protein by using CRISPR tools to cut the stutter out of the mutant gene.

The progress, reported in the Journal of Clinical Investigation [1], comes from the NIH-supported team of Su Yang, Renbao Chang, Xiao-Jiang Li, and colleagues at Emory University School of Medicine, Atlanta. The group’s previous work showed that halting the production of mutated (or even healthy!) HTT protein in mature neurons doesn’t hurt the cells or cause obvious neurological problems in mice [2]. So, the researchers now wanted to see if halting HTT production in millions of neurons in the striatum, which is a part of the inner brain that controls motor skills, could reverse early signs of disease that typically appear in affected mice before the age of 9 months.

To get their answers, the researchers injected millions of inactivated viral particles directly into the striatum of a few 9-month-old mice, engineered to produce the mutant form of HTT protein. Each particle, like a Trojan horse, delivered to the neurons one of the two pieces of the CRISPR/Cas9 editing system: either a short guide RNA sequence to mark for removal the HTT gene’s CAG repeats or a scissor-like Cas9 enzyme to snip out the repeats. In this strategy, both the health and abnormal copies of the HTT gene were “knocked out,” resulting in the production of no HTT protein.

Remarkably, three weeks later, the researchers found that the CRISPR/Cas9 gene editing had reversed the disease process in their mouse model. Neurons in the striatum had stopped making the HTT protein. What’s more, the toxic, abnormal HTT protein that had already clumped together in and around the neurons—and which likely would have would have killed them—had begun to clear to varying degrees in the mice. The same went for other protein abnormalities associated with the progression of Huntington’s disease.

There was even better news to come. The Emory team repeated the CRISPR/Cas9 injections into the striatum of a dozen 9-month-old mice and got a similar protein-clearing outcome. Then, over the next three months, the researchers found that the animals’ balance, muscle coordination, and mobility had improved compared to mice given sham shots of CRISPR/Cas9. Interestingly, the degree of improvement in their motor skills corresponded with the amount of toxic protein that had been cleared from the striatum…”

“…This utilization of CRISPR/Cas9 to pursue a cure for Huntington’s disease is one more example of how this powerful new technology might be applied to the thousands of diseases due to a specific mutation in DNA; efforts are already underway for other conditions like sickle cell disease and muscular dystrophy. Given the promise, the NIH Common Fund is actively exploring ways in which this approach could be accelerated.”

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