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Leber congenital amaurosis type 2: gene therapy improves vision

All three people who received gene therapy at the University of Florida to treat a rare, incurable form of blindness have regained some of their vision.

The report is published in the Human Gene Therapy.

The patients, one woman and two men ranging from 21 to 24 years old with a type of hereditary blindness called Leber congenital amaurosis ( LCA ) type 2, volunteered to test the safety of an experimental gene-transfer technique in a phase 1 clinical research study conducted by University of Florida and the University of Pennsylvania with support from the National Eye Institute of the National Institutes of Health ( NIH ).

In this form of LCA disease, photoreceptor cells cannot respond to light because a gene called RPE65 does not properly produce a protein necessary for healthy vision.
In the study, researchers used an adeno-associated virus to deliver RPE65 to a small area of the retina.

Not only were there no ill effects other than routine postsurgical soreness, the subjects said the vision in their treated eyes was slightly improved in dim lighting conditions.

In this study researchers did not give drugs to suppress the patients' immune system, which was done in two other LCA clinical trials that were under way. This is to prevent the body's defenses and cause a harmful response. However, immune suppression itself carries a risk of infections and other problems.

Leber congenital amaurosis type 2 affects about 2,000 people in the United States and is one of several incurable forms of blindness collectively known as retinitis pigmentosa, which in turn affects about 200,000 Americans.

Children with LCA type 2 experience major visual disability that can lead to total vision loss in adulthood. Although vision loss is severe, the structure of the retina, including its connection to the brain, can remain relatively intact for decades before the photoreceptor cells degenerate.

Source: University of Florida, 2008