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Treating blindness with gene therapy
November 26, 2017, 4:14 pm

Researchers at the University of Iowa in the United States have revealed details of a pioneering gene therapy treatment that could one day see patients who lose their sight to an inherited retinal disease becoming well enough to navigate a maze on their own.

This new, first-of-its-kind gene therapy, which is currently under review by the US Food and Drug Administration (FDA) for potential approval this year, offers hope to patients suffering from a condition called Leber Congenital Amaurosis (LCA). There are currently no treatments available for inherited retinal diseases, such as LCA, which usually begins in infancy and gradually progresses to eventually cause complete blindness.

Data from the first randomized, controlled, phase 3 study of the innovative therapy showed that 27 of 29 treated patients (93 percent) experienced meaningful improvements in their vision, enough that they could navigate a maze in low to moderate light. They also showed improvement in light sensitivity and peripheral vision, which are two visual deficits these patients experience.

Approval of the novel treatment could open the door for other gene therapies that could eventually treat the more than 225 genetic mutations known to cause blindness. For instance, it could be applied to retinitis pigmentosa, another inherited retinal disease caused by a defective gene. Or in the future, gene therapy could possibly provide key proteins needed to restore vision in more common diseases such as age-related macular degeneration.

LCA is rare, affecting about 1 in 80,000 individuals. It can be caused by one or more of 19 different genes. The treatment, called voretigene neparvovec, involves a genetically modified version of a harmless virus. The virus is modified to carry a healthy version of the gene into the retina. Doctors inject billions of modified viruses into both of a patient's eyes.

Treatment does not restore normal vision. It does, however, allow patients to see shapes and light, allowing them to get around without a cane or a guide dog. It is unclear how long the treatment will last, but so far, most patients have maintained their vision for two years. More than 200 patients with LCA have participated in gene therapy trials since 2007.

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