Gene therapy for sight disorders

New clinical trials show that gene therapy can be particularly effective in treating inherited sight problems in children.

Gene therapy - where a defective gene causing an inherited disorder is replaced with a healthy one - was particularly effective in restoring vision to younger patients.

The US-based study followed on from work done by specialists at the Moorfields Eye Hospital in London.

Patients who inherit Leber's congenital amaurosis (LCA) can expect a gradual deterioration in vision which can lead to blindness by the time the patient is 20.

Caused by faulty genes that stop a layer of cells at the back of the eye from working, LCA is one of the top 10 severe sight disorders in children.

All the US patients benefited from the new treatment, measuring a 100-fold increase in pupillary light response - when the pupils constrict in brightness.

But the youngest showed the most marked improvements, with one eight-year-old developing the same degree of light sensitivity as an unaffected contemporary.

After treatment, all the children in the trial gained enough vision to walk without help.

Writing in The Lancet, the researchers concluded that the earlier the intervention, the better the results.

Lead author Jean Bennett said that the the visual recovery noted in the children confirmed the hypothesis that efficacy would be improved if treatment was applied before retinal degeneration had progressed.

She said follow-up studies would be needed to assess whether the treatment altered the natural progression of the retinal degeneration.

The first gene therapy eye operation was carried out at Moorfields and the Institute of Ophthalmology in 2007.

In the operation, the genes are delivered to the eye in a harmless virus. The accessibility and simplicity of the eye make the operation simpler to carry out than other forms of gene therapy.

Experts welcomed the findings but called for more data on dosage and disease progression following treatment.

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