Genetic diseases like Choroideremia are caused by a mutation, or defect, in the body’s DNA. These genetic mutations prevent the body from producing a beneficial protein necessary for certain cells to survive. Gene therapy is a type of treatment for genetic diseases in which the normal gene is delivered into the affected cells, enabling this protein to be produced and restore normal cellular function.
Scientists have tapped into the ability of viruses, like the common cold virus, to penetrate into the cells in the human body. Certain viruses have been modified to prevent them from causing disease in people while still maintaining their ability to enter into cells. These modified viruses, called vectors, have been engineered to carry a normal copy of the Choroideremia gene into the body’s cells and restore their normal function and health. Gene therapy for Choroideremia is delivered through an injection into the back of the eye to provide the vector directly to the affected cells. Clinical trials are currently ongoing to test the safety and the effectiveness of gene therapy for treating Choroideremia patients.
Stem Cell Research
Stem cells are referred to as progenitor cells, which means they can develop into almost all other cells in the body. Historically, stem cells were only obtained from embryos which created significant controversy. However, recent developments have enabled scientists to take a blood or skin sample from an individual and create stem cells from these tissue samples. These stem cells, referred to as IPs cells, can then be influenced to evolve into other cell types in the body by following specific scientific protocols. With these techniques, scientists can use IPs cells to create specific retinal cells, called photoreceptors and retinal pigment epithelium (RPE) cells, which are the cell types lost in Choroideremia. Scientists are currently working to organize these IPs-derived photoreceptors and RPE cells into transplant patches which could be used to replace areas of vision loss.
In addition, stem cells can be used for scientists to learn more about Choroideremia and test future therapies. By creating IPs cells from Choroideremia patients, scientists can study the disease in their laboratory and learn more about its progression at a microscopic level. This information can help scientists to better understand the natural history of Choroideremia in conjunction with tests done at the doctor’s office. In addition, future treatments can be tested on these IPs cells rather than on animal models of Choroideremia which may not respond in the same way as humans.
Doctors commonly prescribe medications to treat a wide variety of diseases affecting the human body. For Choroideremia and other retinal diseases, scientists are working to develop and test medications which can slow down or stop the progression of vision loss.
The genetic defect in Choroideremia causes specific cells in the retina to gradually stop functioning normally, and eventually these cells die off causing vision loss. Scientists are researching different types of compounds that can help to keep these cells healthy. These medications, called neuroprotective agents, can improve the health of the retina by keeping these affected cells functioning and surviving longer, thereby slowing the progression of vision loss. Another area of research involves a specific type of experimental medications called read-through agents. These medications are specifically designed to treat certain types of gene mutations called nonsense mutations, which interrupt the production of the Choroideremia protein causing it to be too short and not function. Read-through agents convince the body’s machinery to ignore this genetic “stop sign” and produce the full-length protein, which enables normal function and health to affected cells. Read-through agents are being tested in clinical trials for other diseases like Duchenne’s Muscular Dystrophy and Cystic Fibrosis.
Vision loss in Choroideremia progressively continues until people lose all their sight. For these individuals, retinal prosthetics research is underway which may be able to provide an alternative to natural vision.
One example of this technology is the Argus II by Second Sight which has been approved by the FDA for use in patients with Retinitis Pigmentosa, a similar retinal disease. Other similar products are currently in development. While users will not regain sight as most people know it, the technology offers the ability to distinguish and interpret light patterns, recognize outlines of basic shapes, people and movement, and improve the ability to navigate more independently throughout the world.