What is the Defect in our DNA?

[Updated 2009 Post] 

A few years ago, I asked one of the doctors on the KDA's Scientific Review Board to describe the defect in our DNA and what it means to those of us living with Kenndy's Disease. His explanation follows:

"The androgen receptor is important for our body's response to male hormones, such as testosterone and dihyodrotesteoserone. The receptor is like a baseball glove, and normally catches ("binds") androgens and then moves them to the nucleus, which is the main control center for the cell. There it helps control the things that make us men (like the genes for watching TV while lounging in our favorite chairs). In Kennedy disease, it is as if the lacing has come out of our baseball glove, and the androgen receptor is not working right. The glove does not have the right shape (it is misfolded), and that makes it hard to catch the baseball well. The androgen receptor can still move to the nucleus, but because it is misfolded, this causes problems. The cell does not work right and eventually might die. And, since this androgen receptor is made by both motor nerve cells and muscle cells, this causes us big problems with moving our arms and legs, and swallowing."

Now for a more scientific explanation, a college professor on the board provided the following:

"In Kennedy's Disease, the defective gene is in the "X" chromosome. The symptoms of Kennedy's Disease are due to a mutation in the gene that produces the androgen receptor (AR) protein. The AR protein acts to mediate all the effects of androgens (testosterone and dihydrotestosterone - male hormones) in cells and in our bodies. Those individuals with Kennedy's Disease produce an altered form of the AR protein, a form that, while it still works well enough mediating the effects of androgens (and so males are still male), produces an additional effect of causing certain spinal cord and brain cells to die. The affected nerve cells are primarily those that control the activation of muscle cells. When the nerve cells die, the muscle fibers that they control shrink and become inactive causing the muscle weakness characteristic of Kennedy's Disease."

Research suggests that the altered form of the AR has problems being recycled (cleaned of all garbage) in the presence of androgens and instead of being completely removed; mutant proteins (the garbage) are only partially digested in the affected cells. This partial digestion of the AR results in the production of AR fragments that, through an unknown mechanism, are toxic to cells. Since this effect is dependent on relatively high levels of androgens, severe muscle weakening is generally not seen in women who carry the mutant form of the AR gene.



Okay, now that I have read both explanations, I feel a little more comfortable. However, I still do not believe I have accomplished what I set out to do today and that was to simplify the explanation. So, I asked "Joe, the Plumber" and he explained the defect like this. “The thingamajig is broken and that causes the whatchamacallits not to work properly.” Now that helps. 😛

Is ASO a potential treatment for Kennedy’s Disease?

This is a follow up to my November 15, 2017, article, “MDAAnnounces SBMA Research Grant.” The research paper was a little over my head (nothing new for me), so I asked the KDA’s resident biology professor, Ed Meyertholen, to explain what Dr. Lieberman’s research was about. Below is Ed’s summary of the grant. For a short primer, I have included the link to a video on DNA-RNA.

"The grant the Andy Lieberman received was to continue the research on the use of Anti-Sense Oligonucleotides (ASO) as a treatment for Kennedy’s Disease (KD). To best understand how it works, it is important to remember the following:

1. KD is believed to be the result of a misfolded protein, specifically, the protein known as the Androgen Receptor (AR).

2. Proteins are built of specific sequences of amino acids, thus to make a protein, one must have amino acids and the sequence of the amino acids of the protein of interest.

3. The sequence of amino acids for any protein are hard coded into our genes - our DNA.  Thus to make a particular protein, the cell must find the gene that codes for the sequence for that protein and read the code to get the sequence.  The structure of the cell that makes the protein is the ribosome.

4. In KD, the misfolded protein is known as the Androgen Receptor (AR) and it misfolds because our DNA has an error in the sequence.  So, when our cells want to synthesize the AR, our instructions are faulty and when we make the resulting protein, it somehow causes cells to die albeit, slowly.

5. Protein synthesis requires two major steps, the first is the synthesis of an RNA copy (RNA is like DNA) of the gene (DNA) which codes for the protein of interest (this occurs in the nucleus).  The RNA synthesis is known as transcription.

6. The RNA copy (which contains the code for the protein) leaves the nucleus and goes to the ribosome.  Here the code is read and the protein is synthesized.  This actual making of the protein is known as translation.

7.  An ASO is a specially designed fragment of RNA that binds only to a specific RNA.  An ASO can be designed to bind specifically to any given RNA.  In this case, the ASO binds only to the RNA that is used to make the AR.  When the ASO binds to the RNA, the cell responds by destroying the RNA (that is what it does) - thus the RNA to make the AR is destroyed before the protein is made and thus no AR is synthesized and thus, it is hoped, no KD.

8.  Andy's grant is, as I understand it, will try to test this procedure on mice models of KD and involve investigating the best ways to deliver the ASO.  Let me also add, there have been several published studies that have shown that ASO's are effective in preventing KD in mice.  Other ASO's have been developed to treat other diseases and just recently, one was approved for use in a disease called Spinal Muscular Atrophy (this is not KD)."  

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.”

Possible new therapy for motor neuron diseases

The University of Sheffield published the following news release yesterday. As always, additional research is required, but the premise is interesting.

New discovery in motor neurone disease and dementia could pave the way to novel treatments

"... When this series of nucleotides is expanded and repeated multiple times, neurodegenerative diseases can occur. The expansions of the gene forms genetic material called ‘R-loops’ which make the DNA vulnerable to breakages. They found that accumulation of R-loops and increased DNA breakage in neurons lead to neurodegenerative diseases.

Our cells have their own repair toolkits specially designed to fix breaks in DNA, however, the products of the expansion over-activate a process called autophagy – a process that gets rid of misfolded or “unwanted” proteins.

The new study, jointly directed by Professor Sherif El-Khamisy from the University of Sheffield’s Department of MBB and Professor Mimoun Azzouz from SITraN at the University of Sheffield, published today (17 July 2017) in Nature Neuroscience, shows that the expansion driven over-activation of this process can degrade some of the very precious DNA toolkits, meaning the cells will eventually die.

“We were able to shut down the out-of-control degradation process, which runs down the cell’s ability to fix genomic breaks, using genetic techniques,” said Professor El-Khamisy.

“Even though the DNA was still damaged, the cells were able to cope and did not die. Discovering this new mechanism and its consequence is a significant step towards developing new therapies for motor neurone disease and other neurodegenerative conditions. ..."

Click on the title to read the entire article.