Using CRISPR to Edit Genes

I have written about CRISPR gene editing several times over the years. I can see  it someday removing the defective CAG repeats in Kennedy's Disease.

Last night, there was a CBS program ’60 Minutes’ featuring CRISPR. The segment was well done. It broke down the actual process to understandable bites of information.

If you missed the program, you can read about it and watch most of it on 60 Minutes Overtime.

I was impressed to learn 2,300 labs across the globe are currently experimenting with CRISPR. And, they have used it to correct a genetic disorder that causes blindness (mouse models only). There is the first U.S. clinical trial using CRISPR for patients with a certain cancer. I also found it interesting that scientists have to consider what could be any unexpected results of correcting the defective DNA.

Below are excerpts of the CBS article:

“Scientists are excited about using CRISPR to treat genetic disease, but the devil's in the details.

Take, for example, treating cystic fibrosis. Scientists know that the hereditary disease is caused by the misspelling of a particular gene. Genes are made up of DNA, which is composed of chemical bases abbreviated by the letters A, T, G, and C. A genetic mutation that causes a disease like cystic fibrosis reads like a typo in the genetic instructions. If scientists can identify the typo, they can program CRISPR to try to correct it with the right sequence.

This week on 60 Minutes, correspondent Bill Whitaker reports on the gene-editing tool. Feng Zhang, a molecular biologist at the Broad Institute of MIT and Harvard, who has been working on CRISPR for seven years, explains how it works.” ...

"You can understand why I want to say, 'It's amazing,' and you also have to be careful and every single cure is going to take a lot of people working together to deliver it," Lander tells Whitaker in the video above. "But you couldn't have imagined such a cure. It wasn't even on your to-do list before CRISPR." ...

"Preventing disease, I think, is a little more complicated because it depends on how we're trying to prevent the disease. Some of them may have undesirable side effects that we don't fully understand," he explains in the clip above.”

Not Everything is Predictable

Those of us living with Kennedy's Disease often like to compare symptoms, CAG Repeats, age of onset, and progression. I believe we do this to feel either better or perhaps worse about ourselves. Unfortunately, not everything is predictable about this gene defect. Allow me to give some examples.

Age of Onset: This could be anywhere from the teens to the 60s. Most often symptoms begin to appear in the 30s and 40s.

CAG Repeats: The number of repeats can be anywhere from the low 40s to the 60s. 34-39 is considered "borderline" and the person might only experience mild symptoms. Researchers now believe the higher the Repeats, the earlier the onset.

Progression and Severity: The earlier the onset, the greater the progression (more severe the condition). This is just a time factor. If onset begins in the 50s for one person and the 30s for another, the 30s person will have experienced 20 years of progression before the 50s person even experiences symptoms.

Symptoms: You would tend to believe that symptoms would be something you could count on, but that is not true either. There is a long list of potential symptoms, but not everyone has the same symptoms, nor do the symptoms appear at the same time in the progression of the disease. Go figure!

What else do we know about the disease?

Pneumonia: This is something that is not kind to us. Almost every doctor encourages us to have the pneumonia vaccination and the booster at age 65. They also recommend the Pneumococcal vaccine today. The flu is something we should also be concerned about because many times it can result in pneumonia. Once again, doctors encourage that you have an annual flu shot.

Exercise: Neurologists have not determined the true value of exercise for those of us with the defect. There is a consensus, however, that exercise if important to our wellbeing. The reason could be as simple as the benefits of endorphins and adrenaline to our general mental, emotional and physical health. Several doctors believe that it is important to continue to stimulate the motor neurons and muscles to keep them healthy as long as possible. And, “muscle memory” is very effective in helping to keep you mobile and upright. Everyone does agree that over-exercising does more harm than good. I can attest to that.

There is also the feeling that exercise and stretching helps "cell inhibition." Cell inhibition is what happens when an activity, such as an exercise, temporarily blocks an unpleasant sensation like a chronic pain. The nerve transmits the pain signal to a cell in the spinal cord that is inhibited by the new "traffic" caused by the stimulus (exercise routine). It is why pinching the cheek blocks the pain from the anesthesia needle in dentistry. Exercise and stretching (working the muscles and joints) produces stimuli for the spinal cord and brain (central nervous system), which is one reason we feel better when we move.

Sedentary Concerns: As the disease progresses, most of us with the defect become less active. We tend to spend more time sitting and do not work our metabolic system. For many of us, "couch potato" is a good phrase that exemplifies our lifestyle as the disease progresses. Weight gain and potential health complications because of the weight, as well as the additional strain on our existing weaker muscles, are always a concern.

Not Everything is KD Related: Just because we have Kennedy's Disease does not mean we are immune to other ailments and health issues. Diabetes, heart and lung disease, kidney failure, as well as many other health concerns are always a possibility as the body ages and based upon hereditary issues.

Continue seeing your regular doctor: Regular physicals and doctor's visits are important for your general health and wellbeing. One man, for example, complained for months about chest pains. He blamed them on Kennedy's Disease and felt he could not do anything about them. The pain finally became severe enough that he saw his doctor. Doctors diagnosed him with having blockage in his arteries.


Please feel free to comment. By taking a moment to share your thoughts you add much to these articles. The articles then become more than just something I said or believe. In addition, by adding a comment, you might just be helping the next reader by sharing your opinion, experience, or a helpful tip.

This is another article snipped from the NIH.gov 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.”

SBMA Study published regarding the AR113Q Muscle

This research paper was published a month ago.

Rescue of metabolic alterations in AR113Q skeletal muscle by peripheral androgen receptor gene silencing

Elisa Giorgetti, Zhigang Yu, Jason P. Chua, Ryosuke Shimamura, Lili Zhao, Fan Zhu, Sriram Venneti, Maria Pennuto, Yuanfang Guan, Gene Hung, and Andrew P. Lieberman1,

Highlights

•Decreased expression of carbohydrate metabolic genes characterizes AR113Q muscle
•AR113Q skeletal muscle shows decreased glycolysis and altered mitochondria
•Peripheral gene silencing by ASO rescues expression of muscle energy metabolism genes
•Altered muscle energy utilization contributes to non-neuronal disease manifestations

Summary

Spinal and bulbar muscular atrophy (SBMA), a progressive degenerative disorder, is caused by a CAG/glutamine expansion in the androgen receptor (polyQ AR). Recent studies demonstrate that skeletal muscle is an important site of toxicity that contributes to the SBMA phenotype. Here, we sought to identify critical pathways altered in muscle that underlie disease manifestations in AR113Q mice. This led to the unanticipated identification of gene expression changes affecting regulators of carbohydrate metabolism, similar to those triggered by denervation. AR113Q muscle exhibits diminished glycolysis, altered mitochondria, and an impaired response to exercise. Strikingly, the expression of genes regulating muscle energy metabolism is rescued following peripheral polyQ AR gene silencing by antisense oligonucleotides (ASO), a therapeutic strategy that alleviates disease. Our data establish the occurrence of a metabolic imbalance in SBMA muscle triggered by peripheral expression of the polyQ AR and indicate that alterations in energy utilization contribute to non-neuronal disease manifestations.