Gene Editing - A Future Disease Cure?
Author: Thomas C. Weiss : Contact: Disabled World
Published: 2015-11-24 : (Rev. 2017-09-22)
Synopsis and Key Points:
Gene Editing has potential to help with diseases like cystic fibrosis or sickle cell anemia, and diseases where a single gene is broken.
Scientists are making tiny scissors called, 'TALEN's,' that can cut and fix a broken gene in a cell. The technology is not ready for use in people yet but when it is it might help people to cure a number of different genetic diseases as long as those diseases are caused by issues with a single gene. The new tool has the potential to help with diseases such as cystic fibrosis or sickle cell anemia, diseases where a single gene is broken.
Gene Editing, also known as Genome editing, or genome editing with engineered nucleases (GEEN), is defined as a type of genetic engineering in which DNA is inserted, replaced, or removed from a genome using artificially engineered nucleases, or molecular scissors. Over the past decade, efficient genome editing has been developed for a wide range of experimental systems ranging from plants to animals, often beyond clinical interest, and the method holds a promising future in becoming a standard experimental strategy in research labs. Gene therapy is a rapidly growing field of medicine in which genes are introduced into the body to treat diseases. Genes control heredity and provide the basic biological code for determining a cell's specific functions.
Something this new tool most likely cannot do is cure more complicated diseases like cancer, where a number of genes are affected. The reason why is because scientists would have to make a different pair of scissors for every broken gene. They would need too many different scissors in our cells.
While this might seem to be incredible, science is a minimum of five to ten years away from finding this technology being used in people. Then scientists need to get the things into a person's cells. After that, doctors might finally start clinical trials with a small number of people. If the trials go well, we might see TALEN's being used in a number of clinics and hospitals around the world.
Broken Gene Editing
At times when a gene is broken, it might cause a disease. Certain differences in the, 'CFTR,' gene may lead to cystic fibrosis. Changes in the, 'HBB,' gene may lead to sickle cell anemia. An obvious way to cure diseases such as these is to, 'fix,' the broken gene, although this is not as easy as it sounds.
People cannot simply search for and then replace in our DNA. Yet what we can do is make a sort of biological editing tool called a TALEN. The strange hybrid of bacterial genes can work with the cell's own machinery to fix a broken gene. The first thing a TALEN needs to do is to find the broken gene in a person's DNA, an important first step because if it cannot find that one, broken gene - it could land on other genes in the cell. If this occurs, the person will have lots of cuts in their DNA, something that is greatly undesired.
Targeting only one spot in one single gene was by far the most difficult part of making a TALEN. The reason why is because people have more than 25,000 genes spread out over their six billion letters of DNA. Without the assistance of a plant bacterial gene called, 'TAL,' scientists might have struggled for years to find a way to discover this needle in a haystack.
A certain family of plant bacteria infects its host by injecting a protein, TAL, into the plant cell first. The instructions for making this TAL protein are found in the TAL gene. TAL proteins can recognize a unique DNA sequence of A's, C's, G's and T's. The TAL proteins use these DNA sequences to find and turn on genes that help the bacteria get inside the cell. Usually, this is bad news for the plant, although it is good news for scientists and perhaps for people with forms of genetic diseases.
Scientists have cracked the code that TAL proteins use to find the correct gene. It turns out that TAL proteins are made up of different building blocks. Every building block recognizes one DNA letter. Using some molecular tricks, people can now mix and match these building blocks in the laboratory. The result is a TAL protein that can find and go to almost any gene a scientist desires.
Now that scientists have discovered a way to find the broken gene, they need to get their editing tool to cut the DNA where there is a mistake. To accomplish this, they turned to a second bacterial gene. Bacteria have genes called, 'endonucleases,' designed to cut up any foreign invading DNA. The primitive immune system helps to protect bacteria from viruses.
To make a TALEN, scientists combine the TAL that recognizes the broken gene with the endonuclease that will cut it; TALEN and endonuclease equals TALEN. Yet they need to do more than simply cut the DNA; scientists must repair it as well. The next step is to past in a working copy of the broken gene. A cell does not know what a working gene looks like, so it cannot just add the right DNA letters to correct the mistake by itself. Scientists can help it out by adding the proper DNA sequence.
After the TALEN makes a cut and the proper DNA sequence is added, a cell does the remainder of the work. Cells already can and do repair mistakes in their DNA via a process called, 'homologous recombination.' Scientists are simply hijacking a system that is already in place and make it do what they desire. The system has worked fairly well in the laboratory; the big question is whether or not it will work with people.
TALEN's and Curing Diseases
Scientists have been able to use TALEN's to edit genes in cells in the laboratory. They accomplish this by designing TALEN's to a gene they desire to edit. Scientists then add TALEN's to the cells along with the new DNA that they want to paste into the broken cell.
Editing genes in cells in a petri dish is certainly one thing; the next challenge is to use TALEN's to cure human disease. Scientists are still working on solving this issue and they certainly have their work cut our for them (no pun intended). The main issue is fixing the gene in a high percentage of cells. Getting TALEN's into a cell is not easy, if the procedure is gentle, too few cells picks up the TALEN's. Yet if the procedure is too harsh, too many cells end up dying.
Additional issues include ensuring the cell with the fixed gene or its descendants remain around for the lifetime of the person, as well as making sure the gene editing is done at a beneficial time in a person's life. Sickle cell disease is a wonderful candidate for TALEN treatment. Scientists have already created the needed TALEN's to target and cut the HBB gene; now they just need to get it into enough cells.
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