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Gene Therapy and Eye Disease

Gene Therapy and Eye Disease:


One of the biggest frustrations I have had as an eye doctor is that often once we diagnose a disease there is very little we can do to cure or alter the course of that disease.    This is especially true with some of the more devastating eye diseases that are genetic like Retinitis Pigmentosa and Leber’s Congenital Amaurosis.  Gene Therapy offers the potential, in the future, to truly help these patients regain or maintain their vision and their independence.


This post is not intended to be an in depth scientific explanation of genetics because that would be boring, but rather a quick overview of gene therapy and the potential these therapies hold to improve the lives of many people who suffer from vision loss caused by genetic diseases.


First some quick definitions;


DNADNA: The complete genetic code that makes an organism.  Each cell within an organism contains this complete set of instructions.  Basically DNA is the recipe for you and I or any other living thing.


Genes: The individual genetic codes that cause particular traits to be expressed.  Whether your eyes are blue or brown is determined by which gene is present in your DNA.  Your risks for certain medical conditions are determined by the presence or lack of certain genes.  Genes also control what a particular cell within the body does.  While every cell within the body contains the complete genetic code or DNA, only certain genes are turned on in each cell.  Which genes are turned on determines what a cell does.  Heart cells are heart cells because the heart cell genes in the DNA are turned on.  There are approximately 20,000 different genes in the human DNA.


Mutation:  The changing of the structure of a gene.  Since the structure of a gene determines what it does, changing that structure changes what it does.  Effects of mutations in genes can have wide ranging effects both positive and negative.  Think of the X-Men.  Their mutations gave them amazing powers but also challenges.  Now back to the real world.  I have 2 red headed daughters.  I read an interesting article in National Geographic this weekend that taught me that the gene for being a redhead resulted from a mutation.  Not only is there a change in hair color associated with this mutation but also a change in perception of pain making them more susceptible to pain caused by heat or cold.  Redheads also require more anesthesia to control pain then the rest of us which is something my wife and I had noted following surgery for one of our daughters.  While their hair is beautiful, it comes with a cost.


What Causes Genetic Diseases?


Genetic disease result when one of three things occur;


  1. A gene is present or turned on and when it should not be.

  2. A gene is missing or turned off that is needed for some essential function.

  3. A gene has mutated.  The genes recipe has been changed so it makes the wrong thing.


These errors can occur because of faulty genes being passed to offspring by parents( heredity) or can occur due to spontaneous changes( mutation) in the genes of an individual.


Gene Therapy in Theory:

Gene therapy is based on this thought,  what if we could turn on a gene that needs to be turned on, turn off genes that need to be turned off or rewriteHow Viruses Work the recipe for genes that have mutated, that could solve a lot of problems.  The challenge is how do we get into cells to do this.  One of the potential methods happens to use something we all have experience with, viruses.


Gene Therapy We probably hear more about viruses infecting our computers then our bodies these days and looking at them in that way is a good way for us to understand what a virus does.  In our computers viruses are small pieces of computer code that hijack our computers for their own nefarious purposes.  In our bodies viruses inject small pieces of genetic code or genes into the cells and hijack them to producing more viruses.  All of us have experienced the downside of these nasty critters in the form of cold sores, colds, the chickenpox or shingles.  Now researchers are finding ways to to alter or mutate what viruses inject into cells.  Turn about is fair play right?  Instead of a piece of genetic code that replicates more viruses, they can insert a missing gene or instructions to turn on a gene.  It could also turn off a gene or even insert a corrected piece of code to replace a mutated one.  The result would be to restore normal function to a gene, a cell or even an organ and the curing of a disease state.  Now that is awesome in theory but does it work?  


Gene Therapy Results:


Results are promising in conditions that are caused by a  defect in a single gene that can be identified.  One such disease is Leber’s Congenital Amaurosis, a retinal condition which causes severe visual impairment from birth.  A defect in a gene called RPE65 was identified as the cause.   An modified Adenovirus( a common virus that causes pink eye) containing a correct copy of the RPE65 gene was used to insert that gene back into the retinal cells.  All patients who participated in the study were found to have improved vision.  So in this case it was shown to work.


In diseases such as macular degeneration and glaucoma where many genes and lifestyle issues have a part, gene therapy has not shown as much promise but lets see what the future holds.

Here’s the take home, Gene Therapy shows  promise for conditions that are caused by identifiable genes.  In conditions where many genes and combinations of genes play a role it does not show as much potential  Gene therapy probably will not play a role in protecting a lot of my patients vision, but for those few who it will help the future is bright.

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