Gene Therapy Is Shedding Light on Vision Loss

Gene Therapy, health
A new gene therapy is shedding light on vision. The condition is known as choroideremia, which gradually causes vision loss with age. There are currently no available treatment options for choroideremia; however, a recent gene therapy may offer hope for patients suffering from the condition.

Choroideremia is a rare condition that affects approximately one in 50,000 people. The condition is the corollary of a mutation in the CHM gene located on the X chromosome. Signs of choroideremia begin at an early age and are more common in males. The mutation weakens light-sensitive photo cells at an early age and ultimately causes them to cease functioning entirely. A recent study published in The Lancet illustrates how a form of gene therapy is shedding light on vision loss by correcting this mutation.

Gene therapy has had a bad wrap in the media lately. Perhaps the most prevalent reason is the widespread mistrust toward genetically modified organisms (GMOs). However, gene therapy became less acclaimed by scientists when a collection of early studies found the method to lead to instances of cancer and death. Due to this, gene therapy has not been authorized as a treatment option for patients in the Unites States.

Yet gene therapy is beginning to make a comeback in the scientific community. Only a few years ago, gene therapy was utilized to combat a renal disease known as Leber congential amaurosis in a three-stage clinical trial. Furthermore, European regulators were the first approve a gene therapy in November of 2012 to treat a condition that thwarted patients from properly digesting fats.

The gene therapy used to treat choroideremia consists of substituting the mutated gene with a correct copy of the CHM gene. Genes are bundles of DNA located inside the nucleus of cells. In order to implant the desired trait, scientists must plant the gene into the nucleus of the cell, yet cells have a natural resistance to outside intruders. However, bacteria and viruses are efficient at combating this resistance. Scientists will therefore mix the gene with a genetically altered version of the adeno-associated virus (AAV) in order to impregnate the cell with the desired trait.The researchers removed a large junk of the virus’s DNA and substituted a corrected vision of the CHM gene. The researchers then injected billions of viral particles into the host, each copy containing a corrected version of the CHM gene.

The gene therapy was performed on six participants who ranged from 35 to 63 years in age. The severity of choroideremia varied with respect to each patient. Exactly four of the patients had lost their peripheral vision; whereas the remaining two patients were beginning to show signs of total vision loss. Although some of the patients did not have substantial vision loss, all of them showed significant thinning of the retina In six months, all of the patients visual acuteness had improved. In addition, the two patients who were beginning to show signs of vision loss showed signs of substantial improvement in their immediate sight. In fact, one of the patients could accurately read three extra lines on an eye chart. Although researchers do not yet know the long-term effectiveness of the gene therapy, all of the patients have continued to maintain their vision two years after the procedure.

The study is too small to deem anything conclusive, however. The team of researchers plan to use the gene therapy on a larger sample of patients consisting of 30 people. The group also hopes that the gene therapy can offer clues to treating all forms of vision loss. Although the treatment is in its early stages, the gene therapy is shedding light on vision loss.

By Nathan Cranford


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