Genetic Eye Diseases and the Possibility of Genetic Therapy
Having taken my bachelor of science majoring in genetics I have always found eye diseases and their relatedness to genetics a very interesting topic. To start off this article I will provide you with a brief introduction to genetics, and then I will talk about eye diseases that have genetic mutations. Finally, I will talk about genetic therapy and its possible uses in rescuing, preventing, and possibly even correcting eye diseases.
Genetics: A Brief Introduction
Since the 1950s when Watson and Crick discovered the structure of DNA, genetics has been a huge influence on the health of humans today. Genetics is the basis of molecular cells, which means that genetics is the basis for life. Genetics is comprised of many things but we will focus on the main components of genes. Genes determine what a specific individual will obtain, for example specific genes and their interactions will determine what eye color you will have. These genes are passed on from the parental generation to the offspring, so if a parent has a specific mutation then the offspring from the parent has a chance of obtaining that mutation. Luckily for us our body is able to detect these mutations and is able to fix them, so very few mutations actually affect us. However, mutations/alterations of our genes are still possible and are seen in many individuals. With genetics one is able to determine how a disease may potentially transform, and how to correct these diseases.
Eye Diseases: The Link Between Genetics and Specific Eye Diseases
There are many eye diseases. Some are due to infections, some are due to genetic disease, and there are others that we have not determined the cause of yet. Many common eye diseases have been linked to a mutation in the genetic lineage of the individual. An excellent and well-studied example of this is retinitis pigmentosa (RP). RP is a disease that causes the rods and cones of the retina to degenerate, causing an individual to lose peripheral vision and possibly become blind. Another commonly studied genetic disease is choroideremia – this disease causes the choroid to become degenerative, which could leave individuals with blind spots in their vision. The choroid is a non-pigmental layer of the eye between the retina and the sclera that functions as an oxygen supplier while absorbing light.
Retinitis pigmentosa is a progressive breakdown of the rods and cones in the retina and occurs in 1/3500 individuals (1). The rods are the first cells to deteriorate, and this degeneration of cells then progresses into the field of vision as the disease becomes worse. The disease may be first noticed with night blindness as the rods of the retina are deteriorated. Rods are a low light (scotopic) photoreceptor found primary in the peripheral retina. This specific disease has three distinct types of inheritance: autosomal dominant, autosomal recessive, and X-linked. There are many genetic mutations associated with RP the main four being RHO, RP2, RPGR, USH2A genes.
Choroideremia is the loss of cells in the choroid, retinal pigment epithelium, and the photoreceptors layers. This loss of cells can impact the vision of an individual starting with peripheral vision loss and then leading towards tunnel vision and can end in blindness. Mutations in the CHM gene will alter the instructions given to the REP-1 escort protein causing REP-1 to not bind to the Rab proteins in the cell, which then obstructs the intracellular trafficking in the cell. Without the ability of REP-1 to bind to the Rab proteins, the cells that required Rab will die and cannot be regenerated. Choroideremia is an X-linked mutation that is inherited by an X chromosome mutation, and predominantly affects men. This disease is seen in 1/50 000 individuals (2).
Gene Therapy: How It Can Help Treat Genetic Eye Disease
Gene therapy has been around since the 1970s, and has been useful in some cases to save individuals. Unfortunately there has been a lot of negative media associated with this technique because it does not have a high integration rate. Gene therapy is basically the insertion of a specific gene into a certain area/cell of your body in an attempt to incorporate it into the DNA of the individual. This is a very hard technique to master because of the insertion process. It is difficult to determine where exactly the insertion can occur and where the best take up of the new/correct gene will occur. However, once the area is determined, the rest becomes a waiting game for the new gene to be incorporated into our DNA.
Researchers as the University of Alberta in the Ophthalmology department have recently began an experiment with Choroideremia patients and genetic therapy to determine if the insertion of a gene will work in slowing down or stopping the disease. As of right now they have not begun trials yet, but have individuals signed up for the procedure. The procedure will involve using a vector in which they will insert gene. They will then inject the vector under the retina with a needle and allow the vector to form a separation between the layers of the retina. They hope that this direct injection into the retina will provide the cells with the correct CHM gene, and that they will uptake the gene and the spread of the disease will halt. If this does work there will be many doors open to eye disease problems.
I have attached the website for the specific gene therapy taking place at the University of Alberta if you are further interested in their research.
Special thank you to Dr. Colin Hobson for reviewing this article and providing me with some insightful information about retinitis pigmentosa and choroideremia.