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Trial Shows Gene Therapy Helps Treat Genetic Eye Disease

Robert MacLaren

Robert MacLaren (University of Oxford)

Researchers at University of Oxford in the U.K. report initial results of a clinical trial showing healthy genes injected into the retinas of patients with a rare inherited disease improved their vision after six months. Findings from the study led by Oxford eye surgeon Robert MacLaren are published in today’s online issue of the journal The Lancet (paid subscription required).

MacLaren — with colleagues from Oxford and institutions in the U.S. and elsewhere in Europe — studied a treatment for choroideremia, an inherited eye disorder that affects 1 in 50,000 to 100,000 people, especially male children and young adults, and believed to account for about 4 percent of all blindness. Choroideremia is a progressive disorder, starting first as an impairment in night vision, and leading to loss of visual acuity (loss of detail), caused by wasting away of of light-sensitive tissue in the back of the retina, and supporting blood vessels.

The disease is the result of a mutation in the CHM gene that causes an absence of the REP-1 protein needed to transport other proteins needed for healthy functioning of cells in the retina. The therapy developed at Oxford uses a viral vector, a safe form of virus that encodes the healthy genetic sequence of the REP-1 protein injected into the retina via surgery. Delivery of the healthy REP-1 protein then aims to restore transport of the proteins needed for proper functioning of the retina.

The trial’s main purpose was to test the safety and tolerability of the gene injections with up to 12 choroideremia patients, but also to report any benefits from the treatments, defined as slowing down of the degeneration of the retina. The patients received the gene injections in one eye, to allow for comparison with the other eye. The injection procedure, says the university, resembles cataract surgery, where the retina is detached, and injections made with a fine needle under the retina.

The paper reports the results of the tests after six months with six patients having varying levels of severity of choroideremia who received the treatments. (Three other patients since enrolled in the trial and been treated at higher doses.) Before the treatments, four of the patients experienced loss of night vision, but still maintain good to excellent visual acuity. Two of the patients had poor visual acuity, as well as loss of night vision. The trial tested visual acuity — ability to see levels of detail — by reading lines of letters on an eye chart, as well as night vision.

After six months elapsed following the injections, the two patients with reduced visual acuity were able to read two to four more lines of letters on the chart with their treated eyes. In a statement, University of Oxford reports the two patients maintained their visual acuity for 1 to 2 years after treatment. The four patients with good to excellent visual acuity maintained those levels, but also improved their night vision.

While choroideremia is a rare disorder, MacLaren believes the treatments may be applicable to more common inherited eye conditions. “This has huge implications,” says MacLaren in a university statement, “for anyone with a genetic retinal disease such as age-related macular degeneration or retinitis pigmentosa, because it has for the first time shown that gene therapy can be applied safely before the onset of vision loss.”

MacLaren and colleagues at Oxford applied for patent protection for the discovery, through Isis Innovations, the university’s technology transfer office.

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