There are many causes of blindness and vision loss, including genetics. Research is under way to develop ways to “fix” errors in the genetic code to give new sight to people with conditions such as retinitis pigmentosa and Leber congenital amaurosis (LCA).
Gene therapy is all about finding ways to fix problems with the body’s genetic code. When a man and woman create a baby, each parent provides half of the genetic information needed for the child to grow and develop. The woman’s genes are represented in her egg while the man’s genes are shared in his sperm. When an egg is fertilized, the genetic code from the woman pairs up with the matching part of the code from the man to create a complete set of instructions for the new baby.
The genetic code is a complex system of triggers that controls every aspect of how the body works, from telling cells whether they should grow into muscles or hair to telling the body how to produce the many chemicals and other substances it needs to function correctly. Because the genetic code is so complex, there are many things that can go wrong. Using gene therapy, scientists are working to figure out what each tiny piece of the code is responsible for and to find ways to fix things in the code when they do go wrong.
In the field of vision, researchers at the University of Pennsylvania are working with dogs that have congenital achromatopsia, which is total color blindness. A similar condition affects about one out of every 30,000 to 50,000 people. This condition results when the cones, or color sensing cells in the retina of the eye do not function correctly. Using gene therapy, the researchers have been able to cure this condition in young dogs, which have a gene structure that is a closer match to human genes than that of the mice which were used in previous studies. The treatment has been effective for over 33 months and appears to be permanent. This successful treatment in dogs brings researchers one step closer to finding a way to use gene therapy to cure this condition in human patients.
Researchers are also working with canine patients to develop a process to repair defective rods, which are photoreceptors in the eye that help us see in dim light. Research involves using a virus to carry new genetic information into the cells in the eye. A virus normally carries its own genetic material that can make us sick. In gene therapy, researchers remove the bad genetic information from the virus and replace it with the good genetic information they need to add into the cells. When the virus is injected into the area, it carries the good information into the cells where it can help fix the genetic code. Researchers at the Universities of Pennsylvania and Florida used these viral carriers to test three different chemicals to try to fix the rods in the eyes of dogs. Two of the three proved to be successful. The researchers are hopeful this type of gene therapy will provide a safe and efficient way to correct the genetic errors that cause retinitis pigmentosa and other genetic vision problems.
These are just two recent examples of on-going gene therapy in the field of vision. More testing will need to be done before these techniques are approved for testing on human patients, and clinical trials will be needed before the treatments could be approved for general use.