Gene Therapy Trial Shows Promising Results in Treating Rare Type of Blindness

Researchers at the University of Oxford and colleagues have used gene therapy to prevent blindness in six patients with a rare genetic disorder called choroideremia that leads to progressive vision loss.

Researchers are hopeful that the treatment will help prevent blindness in people suffering from common eye diseases such as macular degeneration or retinitis pigmentosa.

The clinical trial on the gene therapy was conducted on a set of people with choroideremia. The therapy, scientists said, has surpassed expectations ultimately preventing loss of vision in the participants.

"My left eye, which had always been the weaker one, was that which was treated as part of this trial...Now when I watch a football match on the TV, if I look at the screen with my left eye alone, it is as if someone has switched on the floodlights. The green of the pitch is brighter, and the numbers on the shirts are much clearer," said Jonathan Wyatt, 65, one of the study participants

What is Choroideremia?

Choroideremia is a rare genetic condition which leads to progressive loss of vision, especially in males. The condition affects one person in every 50,000- 100,000 people. The numbers might be higher due to under-reporting of cases as the condition is somewhat similar to other eye-diseases.

Usually, the first symptom of the condition is night blindness followed by tunnel vision and lack of visual acuity, which is measured by the number of lines that a person can read on the sight chart.

People with the condition suffer from a degeneration of choroid and retina, caused by a lack of RAB Escort Protein-1 (REP-1).

The condition is caused by mutation in the CHM gene present on the X chromosome. Without the protein produced by this gene, the pigment cells in the retina slowly begin to die. Due to the cell death, the rest of the retina usually shrinks, reducing vision. There is currently no cure for the condition.

Gene therapy Trial

The idea behind the research was to see if a virus could be sent to restore the missing gene in the retina.

The team used a safe virus to send CHM gene to the light-sensing cells in the retina. The surgery was somewhat similar to cataract- the patients' retina was detached and the virus was injected under the retina using a fine needle.

Six people with the condition underwent the therapy; two of them had reduced visual acuity, two had good acuity and the other two had excellent visual acuity, meaning that they could read the letters on the sight board more clearly than others.

After six months, patients with good and excellent visual acuity had the same levels of visual clarity. They could see more in the dark, despite having undergone a surgery that had detached the retina.

The best results were seen in people with reduced visual acuity as they could read more lines on the sight board.

According to researchers, the therapy might help preserve visual acuity. "If we were able to treat people early, get them in their teens or late childhood, we'd be getting the virus in before their vision is lost," explained Robert MacLaren of the Nuffield Laboratory of Ophthalmology at the University of Oxford in a news release. "If the treatment works, we would be able to prevent them from going blind."

Researchers still aren't sure whether effects of the therapy will last for long. Results of the first six months of the trial are published in The Lancet medical journal.