CRISPR-Cas9 Gene Editing Technology: A Cure for Cystic Fibrosis?
When Kathi Clapham was born, she was diagnosed with a genetic lung disease called Cystic Fibrosis. Her family was told that her disease was incurable, and that it would have a major impact on her body and lifestyle. However, with the right treatment and care, they were told, she would be able to manage her symptoms and lead a relatively normal life.
Kathi found she was able to manage her condition quite well for most of her life, until she found out she was pregnant with twins. Her pregnancy began to take a major toll on her body and lungs. She was afraid of the effect it might have on her twin babies, and was struggling immensely with her health.
Kathi was on a constant ventilator for oxygen, and her health and lung capacity was rapidly deteriorating. After having her twins, she was placed in a medically induced coma to allow her body to heal. When she awoke, it was clear that the only option left was a double lung transplant.
For weeks, Kathi waited for the call which signified a new set of lungs. When the call finally came, Kathi and her husband rushed to the hospital for the lung transplant. The surgery was successful, and she was on the road to a full recovery. A few months after the surgery, she could finally breathe with ease.
Kathi’s story had a happy ending, but not everyone’s does.
Cystic Fibrosis impacts over 30,000 adults in the United States alone.
Although it may seem that lung transplants are an optimal treatment option to cure Cystic Fibrosis, this is not the case. Lung transplants are unfortunately not a scalable option to cure Kathi’s condition, due to a number of reasons.
Firstly, donor organs are extremely limited in supply, with only about 1,000 transplants being performed each year in the whole of the United States. Furthermore, it is extremely difficult to obtain a set of lungs that is compatible with any given patient, and many donor lungs are deemed unsuitable due to factors such as damage and trauma during retrieval, or infections.
There is also a major shortage in public organ donor awareness, with many people unaware of organ donation, or even unwilling to donate. There are many technological limitations which can prevent transplant surgeries from being performed, as the advanced medical equipment and technology required is in very short supply. The technology is limited and much less accessible in underdeveloped countries with resource constraints, making it an extremely difficult and risky procedure in many regions.
What is Cystic Fibrosis?
Cystic Fibrosis (also referred to as CF) is a genetic condition which impacts the respiratory, and in some cases, the digestive system. It is caused by a mutation(s), or error, in a person’s genetic code.
Genes are composed of 4 letters: A, C, T, and G. These letters are arranged in specific patterns, and this pattern is called the genetic code of that organism. The genetic code of an organism, put simply, acts as an instruction book, to tell the cells and body how to operate. It determines an organism’s physical characteristics, development and growth, longevity and aging, nutrient and biochemical processing, and in some cases, inherited disorders.
Sometimes, there is a mistake in the arrangement of these letters. This is called a mutation. Every organism, including you, has hundreds of mutations in their genetic code. Most of these mutations are harmless, and have no discernible effect on its health or physical traits. However, in some cases mutations cause undesired adverse effects, such as diseases or conditions. This is the case with Cystic Fibrosis.
Cystic Fibrosis is a condition which results from a mutation in the CFTR (cystic fibrosis transmembrane conductance regulator) gene. This gene is responsible for producing CFTR protein, which is a protein found in the cell membranes of cells in the respiratory and digestive system. This protein’s primary function is to allow for the flow of chloride ions in and out of cells in the respiratory system. This, in turn, regulates the movement of salt and water in and out of the body’s cells, and is extremely crucial to ensure the movement of mucus in the respiratory passages.
Normally, in a healthy respiratory system, hair-like structures called cilia move in a coordinated manner to move and push debris and foreign particles out of the respiratory passageways. However, if a mutation is present in the CFTR gene, the cilia often do not move at all, causing buildup of sticky mucus in the lungs.
The effects of this condition can result in a chronic cough, recurrent lung infections, breathing difficulties, and digestive complications. These symptoms have an extremely negative effect on the every day lives of Cystic Fibrosis patients, and the life expectancy for a CF patient is only about 40 years.
Treatments that are currently being used include airway clearance techniques, antibiotics, anti-inflammatory medications, inhaled medications, pancreatic enzyme replacement, CFTR modulators, and, as a last resort, lung transplantation. So, it seems like there are a number of great treatment options available, doesn’t it? Obviously, we have Cystic Fibrosis completely under control with the wide range of treatment options we have developed, right?
Unfortunately, this is far from the truth. Cystic Fibrosis still continues to impact over 30,000 adults in just the United States. Although we have developed treatments for the disease, none of these are cures.
With so many treatments available, why is it that we still do not have a feasible option to actually cure Cystic Fibrosis?
Actually, we do. Allow me to introduce you to CRISPR-Cas9.
What is CRISPR-Cas9?
We’ve talked about genes, cells, and mutations. To recap, Cystic Fibrosis is a condition caused by a mistake in a person’s genetic code.
What if I told you, we can edit that code to remove the mistake and cure Cystic Fibrosis.
This is a process is called gene editing. A brand new, revolutionary technology called CRISPR-Cas9 has made it easier than ever to remove and replace mutated genes.
But, what exactly is CRISPR-Cas9? How does it work? Let’s break it down.
If we misspell a word in a document, we can use the search function to locate the misspelled word, and the delete function to remove the misspelled word. We can also edit the word by changing one of the letters to make it correct.
Now, take this analogy, and apply it to genetics. CRISPR-Cas9 (CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats) is a technology which can locate, cut, paste, and edit genes. This works to edit the mutations in genes that cause diseases. Here’s how it works:
There are two main components to the CRISPR-Cas9 technology, the guide RNA, and the Cas9 enzyme.
The guide RNA acts as a molecular GPS system, which, when inserted into body, locates the specific gene sequence scientists are attempting to target. It is a strand of RNA, made of nucleotides, which are the same chemical units that DNA is made up of. This RNA designed to match the specific nucleotide sequence of the target gene.
The Cas9 enzyme is attached to the guide RNA, and acts as a pair of molecular scissors. Its purpose is to cut the mutated piece of DNA at the correct spot in the genome, which it is directed to by the guide RNA.
Once both of these components are developed and attached to each other, they are ready for delivery. Typically, the guide RNA and Cas9 enzyme compound is inserted into the target cell(s). This can be done using a number of methods. Let’s examine the two most common delivery methods. The first, and most common method is plasmid DNA. Plasmid DNA is a small, circular package containing the CRISPR-Cas9 compound, which is introduced to the cells through injection. These can independently replicate, and are most commonly used in biotech and genetic research sesttings. Alternatively, viruses can also be utilized as carriers for the compound. The viruses carry the compound into the cells, similarly to the plasmid DNA method. These viruses function as delivery vehicles, with the CRISPR-Cas9 compound being attached to them. Once the virus has deposited the compound inside the cell nucleus, it is discarded by the cells.
Once the CRISPR-Cas9 compound has been introduced to the cells, it is time for the guide RNA to locate the target gene, and guide the Cas9 enzyme to the correct location. The Cas9 then makes a double-strand break in the DNA at the target location. This is when both sides of the DNA are cut at the mutation, creating two separate pieces of DNA. When this cut is made, the cell’s natural DNA repair mechanism is triggered, and kicks in to repair the cut gene.
There are now two ways to repair the broken DNA. The first method is referred to as Non-Homologous End Joining (NHEJ), which is the most common method employed independently by the cell’s own processes. This is a natural process, and does not require intervention by scientists. During this method, the cell attempts to join the two broken ends of the DNA strands. This method is can be described as the cell attempting to “duct tape” its broken ends. However, this is not always a very precise method, as it can result in unintended insertions or deletions of genetic material, which disrupts the function of the target gene, and can sometimes cause new problems.
The second method to repair the break in the DNA is called Homology-Directed Repair. This repair process is not a natural repair process, instead it is directed by scientists. Essentially, instead of breaking the undesired mutation, an extra step is added to edit the DNA to be precisely what is desired. During this method, scientists can attach a repair template to the guide RNA and Cas9 compound, which tells the cells how to repair the break. The repair template attaches to the target location, and tells the DNA exactly how to repair the break with the right genetic code. This is normally a more advanced and specific technique, and is used to insert specific new DNA sequences to the target site, or to create desired genetic changes.
Applying CRISPR-Cas9 to Cystic Fibrosis
If you haven’t guessed already, CRISPR-Cas9 is going to absolutely revolutionize the healthcare industry. This new breakthrough in gene editing technology means that a disease that was once incurable can now be completely eliminated with just a single injection.
In the case of Cystic Fibrosis, where there is a known mutation in the CFTR, we are now able to apply CRISPR-Cas9 technology to eliminate and repair the errors that cause this condition. This would allow for the flow of chloride ions in and out of respiratory cells, allowing mucus to pass through respiratory pathways easily. This would automatically relieve patients of symptoms associated with Cystic Fibrosis and cure the disease.
Lung transplants and the complications that come with them will no longer be required to treat Cystic Fibrosis. With CRISPR-Cas9, no repeated treatments are required, and there is no lengthy recovery process.
The technology is currently in its trial stage, meaning it is continuously being tested and modified. When it is open to the general public, this technology will immensely benefit the 160,000 people worldwide that are impacted by Cystic Fibrosis, and potentially eliminate the disease for good.
The potential of CRISPR-Cas9 technology is virtually limitless, and will undoubtedly dominate the healthcare industry in the coming decade, opening doors to major scientific and technological advancements in medicine.
