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.”

A question concerning CAG repeats

I recently received the following question this week:

“Do you know of any understandable explanation of CAG Count and its importance and implications to SBMA sufferers? Everything I have found is pretty unintelligible to me (and I thought I was a pretty intelligent kind of a person!!). From what I can gather the count length - whatever that is (& I have no idea of mine) is important to diagnosing the condition but is of no particular relevance in assessing the outcome. Is that correct?”


So I consulted our biology professor and asked for help. Ed provided the following explanation of the DNA mutation and Kennedy’s Disease. I definitely learned something from his explanation. Thanks, Ed.

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Kennedy’s Disease (aka SBMA) is a genetic disease.  Aside from the fact that this means one inherits the disease from one's parents, this fact has other implications.   The fact that it is genetic also means that there is a change in a gene - a gene being an inheritable factor that influences some trait.  Genes are made of a type of biomolecule called DNA.  DNA, in turn, is composed of long chains of small subunit molecules called nucleotides.  Different genes are linked together to form larger DNA structures called chromosomes.  Humans have 23 pairs of chromosomes (for a total number of 46) and each chromosome can have over a thousand different genes.  Nonetheless, each chromosome in every person should contain the same genes in the same order.  Now since genes are made up of DNA, and genes make up chromosomes, chromosomes contain DNA.  So essentially, the genetic material has a hierarchical structure:  Chromosomes:Genes:Nucleotides.  A simple, similar analogy might be Building:Walls:Bricks.

Now one might wonder what makes each gene different.  As was stated, each gene is made of DNA which is in turn made of nucleotides.  DNA employs 4 different nucleotides: adenine, guanine, cytosine and thymine.  Scientists, being efficient (or maybe lazy) abbreviate these with single letters - A, G, C and T.   Each gene has a specific, unique sequence of nucleotides much like words have a specific, unique sequence of letters.  The primary difference is that each gene's sequence is very long, often in excess of a thousand nucleotides.   The sequence of nucleotides in a gene tells the cell how to make a specific protein, thus each gene codes for the production of a specific protein.  If the nucleotide sequence of a gene is altered (this alteration is known as a mutation), the resulting protein is altered and it may not work normally (and often does not work at all).  The result of such a change may results in changes in the way the cells work and if this occurs, we would say that this would be a genetic disease.  Thus Kennedy’s Disease is due to a mutation in a specific gene that alters the function and structure of a specific protein.

The gene mutated in Kennedy’s Disease is the gene that codes for the protein known as the androgen receptor (AR).  The type of change in the nucleotide sequence in the gene for AR that causes KD is quite unusual.  Usually, mutations are due to nucleotide substitutions or deletions or insertions - but this is not true for Kennedy’s Disease.

Kennedy’s Disease is due to the repeat of a three nucleotide sequence - a repeat of the sequence that is cytosine-adenine-guanine or CAG in the scientific shorthand.   This CAG (pronounces see-a-gee, NOT pronounced so it rhymes with hag) repeat actually occurs in the AR gene in all humans where its repeat number is quite variable.  The repeat only causes Kennedy’s Disease when the repeat number exceeds 40 (CAG repeated 40 times).  Individuals with repeat numbers less than 40 do not have Kennedy’s Disease.  At this time, it is not clear why this causes Kennedy’s Disease (scientists are trying to find out) but it does!

What does the DNA blood test tell us?

At least a couple of times a year someone will write and question the accuracy of the DNA blood test for Kennedy’s Disease. This normally happens because a man has identified many of the symptoms he has are also related to Kennedy’s Disease (KD).

It is my understanding that the DNA test is 99+% accurate. Yes, that still leaves less than one percent available for error. Of course, there is the possibility that a person is ‘borderline’ KD. That means his CAG repeats are 34-39. It is also my understanding that borderline cases can exhibit some of the symptoms, but not all of them. The progression is also not as evident.

The two DNA tests that I had showed a scale similar to the following:

• 0-33 = Normal
• 34-39 = Borderline
• 40 and above = Kennedy’s Disease (Spinal Bulbar Muscular Atrophy or SBMA)

So, borderline could be diagnosed as normal by some doctors and also explain why a patient experiences some of the symptoms.

In a study conducted a few years ago, it was reported that the higher the CAG repeat count the earlier the onset meaning the progression is also more apparent over time. I happen to be on the higher end with a 53. I have known others with counts in the low 40s that did not exhibit any noticeable symptoms until the late 50s or 60s. (Boy would that have been nice)

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Wikipedia defines these type disorders as Trinucleotide repeat disorders (also known as trinucleotide repeat expansion disorders, triplet repeat expansion disorders or codon reiteration disorders) are a set of genetic disorders caused by trinucleotide repeat expansion, a kind of mutation where trinucleotide repeats in certain genes exceeding the normal, stable, threshold, which differs per gene. The mutation is a subset of unstable microsatellite repeats that occur throughout all genomic sequences. If the repeat is present in a healthy gene, adynamic mutation may increase the repeat count and result in a defective gene.


Wikipedia also explains Kennedy’s Disease as: SBMA is caused by expansion of a CAG repeat in the first exon of the androgen receptor gene (trinucleotide repeats). The CAG repeat encodes a polyglutamine tract in the androgen receptor protein. The greater the expansion of the CAG repeat, the earlier the disease onset and more severe the disease manifestations.

Follow-up on earlier article on RNA defect repair

Last Thursday I published information on some recent Kennedy’s Disease research that looked promising even though it had not been verified by another lab.  The article, “Scientists identify compound that can help repair toxic RNA defect,” was interesting even though I didn’t understand most of it.

I asked Ed, our resident biology professor, to review the study and comment on it when he had a chance.  Below are Ed’s comments.

It is a different approach overstates the case with regard to treatment of the various CAG repeat diseases.

As you may remember, it is generally thought that the symptoms of Kennedy’s Disease (KD) (and other CAG diseases) is due to a misfolded protein and that the cells no longer have the ability to remove these proteins and this somehow causes cells to die.  This paper is based on a different proposed mechanism for cell death.  The problem is not the protein but the mRNA.  To make a protein, one needs the instructions on the order of amino acids for that particular protein.  Just like a dictionary tells you the order of letters in a word, DNA (our genes) tells you the order of amino acids in any protein.  To make a protein, one therefore needs these instructions.  Cells get the instructions by looking up the instructions for a protein (as you would look up a word in the dictionary) and makes a copy of the needed instructions.  This copy is made out of RNA is known as m (or messenger)RNA (see * below).  The experiments in this paper are based on the notion that it is actually the mRNA that is somehow causing the cell death and not the resultant protein.  The idea is the mutant mRNA binds to a protein called MBNL-1 and it is the sequestering of this protein that ultimately leads to cell death.  They found a way to prevent the mutant mRNA to bind to MBNL-1 and thus, if this is indeed the reason for cell death, block cell death.  BTW, they did not show that this chemical stops cell death just the mRNA-protein interaction.  Since it is not generally accepted that the mRNA is at fault in KD, it really is a stretch to call this a breakthrough (or even an advancement) that will lead to a treatment.

This is a difficult paper for nonscientists to discuss as the suppositions are not generally accepted and they really did not show any cell saving affects - yet the site you forwarded seems to indicate a major breakthrough.  As you may know by now, I am not a fan of such publicity as it leads to unfulfilled and unrealistic hope.  The work may end up being very important but we are a long way from it being helpful to us and that is certainly not clear in this press release.

(*) From Wikipedia:  Messenger RNA (mRNA) is a molecule of RNA that encodes a chemical "blueprint" for a protein product.  mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosomes. Here, the nucleic acid polymer is translated into a polymer of amino acids: a protein. In mRNA as in DNA, genetic information is encoded in the sequence of nucleotides arranged into codons consisting of three bases each. Each codon encodes for a specific amino acid, except the stop codons, which terminate protein synthesis. This process requires two other types of RNA: Transfer RNA (tRNA) mediates recognition of the codon and provides the corresponding amino acid, whereas ribosomal RNA (rRNA) is the central component of the ribosome's protein-manufacturing machinery.