CRISPR gene therapy cures liver disease

mice with hereditary tyrosinema cured by CRISPR-Cas9
CRISPR-Cas9 cured mice with liver disease

The CRISPR-Cas9 system can be used to edit out gene mutations and correct diseases. It has also been used to tailor make a number of different experimental animals that express exactly the DNA sequence scientists want. This is done by injecting the cells of developing embryos with the Cas9 enzyme that cuts DNA, along with an RNA guide that tells the enzyme where to cut the DNA, and a corrected DNA sequence which will be copied into the cut DNA. All these ingredients work together to edit the DNA sequence to whatever scientists want. Scientists have even used CRISPR to prevent muscular dystrophy in mice.

It is relatively easy to use CRISPR in embryos because they are transparent and easy to manipulate under a microscope. The big problem with making the jump from editing the DNA of embryos to editing the genes of adult animals is getting the gene-editing ingredients into adult cells. We are not transparent and even if we do surgery or insert a camera-tipped catheter probe into the body to find the diseased tissue, it is not practical to inject every single one of our millions of cells.

The thing is, to cure many diseases, we don’t have to inject every single diseased cell. We just need to cure enough cells to reach a baseline function that we label ‘healthy’.

In a recent study, scientists used the CRISPR-Cas 9 system to cure mice with the liver disease Hereditary Tyrosinema Type 1. This disease is caused by a mutation in the Fah gene. The Fah gene makes the enzyme fumarylacetoacetate hydrolase in liver cells. This enzyme controls the last chemical reaction in the pathway that breaks down tyrosine. Tyrosine is one of 22 amino acids that are the building blocks of proteins. Proteins in our cells are constantly being recycled. Old, damaged ones are removed and shiny new ones replace them. Part of the protein removal process is to break up the proteins into their individual components, amino acids. These amino acids then need to be broken down into something that the cell can use to make energy. The energy is then used to make new amino acids and assemble them into new proteins. The circle of life.

Patients with Hereditary Tyrosinemia Type 1 can’t completely break down tyrosine. This means there is a build up of toxic by products in the cells of these patients. This causes liver and kidney problems and mental retardation. Up until now there has been no good treatment for this disease and it is often fatal. Treatment options are a low protein diet, a liver transplant and the drug nitisone. Nitisone blocks a different enzyme that works earlier in the tyrosine breakdown process. Blocking this enzyme stops the buildup of toxic by products that happens when tyrosine is only partially broken down. Nitisone can alleviate some of the symptoms of Hereditary Tyrosinema but it has some nasty side effects including: abdominal pain and bloating; headache; vomiting; weakness; loss of appetite and weight loss.

Mice with the same Fah mutation that causes Hereditary Tyrosinemia in humans develop significant liver damage, lose weight and die if they are not treated with nitisone. In this study, adult Fah mutant mice were injected with copies of the healthy Fah DNA sequence, guide RNA and Cas9. This resulted in normal Fah protein being expressed in 1/250 liver cells in treated mice. Because these cells were much healthier than the cells that still expressed the mutated Fah, they divided and produced more daughter cells. This rapidly increased the percentage of healthy cells in the livers of the treated mice, up to 33% after 30 days. The treated mice also had significantly less liver damage than untreated mice.

One of the reasons this experiment worked was because the genetic disease investigated was in the liver. The liver filters all blood. Therefore anything injected into the blood will affect the liver. In this study the CRISPR ingredients were injected into the blood via the tail vein. The rate of successful DNA editing in this experiment was very low: 1/250. If they were trying to edit genes in another organ like the heart, or worse the brain which hides behind the blood brain barrier, the uptake would have been much lower and this approach may not have worked. Also the liver is a very regenerative organ with a high rate of cellular division and reproduction. Many other organs like the heart and kidney have an extremely low level of cell turnover. So it would have taken much longer to increase the percentage of healthy cells in these organs.

Still it is a very encouraging result that proves that gene editing can treat disease in adult animals.

The Scientific Paper:
Hao et al. Genome editing with Cas9 in adult mice corrects a disease mutation and phenotype. Nature Biotech. 2014.

15 thoughts on “CRISPR gene therapy cures liver disease

    1. However, viral vectors have their place when considering the disorder. As I understand, they have a tendency to be faster and more redundant in their response.

  1. You actually make it seem so easy with your presentation but I find this
    topic to be really something which I think I would never understand.
    It seems too complex and extremely broad for me.
    I am looking forward for your next post, I’ll try to get the hang of it!

    1. Realistically I think it will be 5-10 years. Scientists have to work out a better way to deliver the therapy to the liver cells than the method of high force injection into the mouse tail vein that was used in this study. They also need to optimise the treatment so that more liver cells are edited by the CRISPR technology. Then it needs to go through a series of clinical trials in humans to make sure it doesn’t have bad side effects. If it does make it to clinical trials, your daughter’s doctor might be able to get her enrolled in a trial if you are interested in that. Of course there is a lot to think about before enrolling in a clinical trial because you can’t be sure that there won’t be side effects to the drug, you don’t know how well the drug will work and you don’t know if your daughter will be even given the drug or will be in the placebo group. Sorry I don’t have better news for you.

  2. Thanks , I’ve recently been looking for information about this
    subject for a while and yours is the best I’ve came upon so far.
    But, what in regards to the conclusion? Are you positive concerning the supply?

    1. There’s still a lot of work that needs to be done to improve how CRISPR is delivered to cells. This is a really new technology so it is not clear yet whether there might be side effects to this treatment. I think it’ll be a lot clearer after 5 more years of research. Unfortunately medical research is slow.

  3. From what I am learning, CRISPR cannot pass the BBB and needs to use macrophages? Is this correct? If so, is it still possible to edit the MGMT gene for removal which when methylated does not allow utilization of teozolomide. Thank you.

  4. An impressive share! I’ve just forwarded this onto a coworker who had been conducting a little
    homework on this. And he actually ordered me breakfast simply because
    I discovered it for him… lol. So allow me to reword this….
    Thank YOU for the meal!! But yeah, thanx for spending the time to talk about this topic here on your web site.

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