Could gene therapy cure blindness?

Scientists have come up with a genetic treatment for blindness, one which has proven effective in giving back at least partial sight to people with a rare condition known to lead to complete blindness. The successful procedure has now been backed by the US Food and Drug Administration (FDA) and could lead to renewed interest in the field of gene therapy.

The research led by a team from the University of Iowa addresses the rare condition called Leber congenital amaurosis or LCA which affects one in 80,000 people and is caused by a gene mutation. LCA typically begins to manifest at birth or shortly thereafter and progresses over years, with patients first losing their peripheral vision (creating tunnel vision) and also making it more difficult to see in low light. Over time, patients can lose their vision completely, although the presentation of the condition differs considerably, depending on its particular genetic impact.

LCA stems from a mutation in the gene called RPE65, which is important in making a protein implicated in the proper functioning of the retina. Scientists have used gene therapy in attempt to replace the defective copies of RPE65 with working ones, and so far, the newly created procedure seems to be working.

This past week at the annual meeting of the American Academy of Ophthalmology, researchers presented the results of the first randomized, controlled, phase 3 study in which 27 out of 29 patients (93 per cent) showed measurable improvement in light sensitivity and peripheral vision, both of these measured by maze-walking tests in low to moderate light.

The results are encouraging, as they signal the effectiveness one year into treatment of gene replacement therapy in a previously untreatable medical condition. Last month, a panel of experts for the FDA in the United States approved the treatment, which goes by the name voretigene neparvovec (Luxturna) and is made by Spark Therapeutics of Philadelphia, Pennsylvania.

“It’s the first of its kind,” says geneticist Mark Kay of Stanford University in California, who was not involved with the study, to the science journal Nature. “Things are beginning to look more promising for gene therapy.”

Encouraging results for blindness, but gene therapy has had its missteps…

The field of gene therapy has seen its ups and downs over the past 20 years, emerging in the early 1990s with the potential to cure previously untreatable diseases such as sickle-cell anemia, Parkinson’s disease and hemophilia. The procedure involves injecting a virus carrying a replacement gene into the body, usually at the site where the condition manifests.

But with the death of a patient enrolled in a gene therapy clinical trial in 1999, research and investment in the field grew more cautious. But recent advances have led to renewed interest.

Earlier this year, a Canadian medical team based at the University of Calgary published their research involving the successful treatment for Fabry disease, a rare and life-threatening genetic disorder which affects the body’s ability to produce an enzyme needed to break down a fatty compound which can damage the kidneys.

The new FDA committee approval is a first for gene treatment for eye diseases.

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