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Gene Therapy Preserves Vision in Lab Study of Bardet-Biedl Syndrome

In a groundbreaking effort funded in part by the Foundation Fighting Blindness, scientists at Baylor College of Medicine used gene therapy to preserve vision in mice affected with a form of Bardet-Biedl syndrome (BBS), a devastating, multi-faceted disorder that causes significant vision loss from retinitis pigmentosa (RP). This research advancement represents the greatest success thus far in the development of a treatment for RP associated with BBS.

BBS can affect many parts of the body, causing intellectual disabilities, learning problems, obesity, genital abnormalities, and serious kidney dysfunction, as well as significant vision loss from RP. The range and severity of disorders varies from person to person, though individuals with BBS are usually legally blind by the age of 16. Approximately 2,000 people in the U.S. have the condition. While BBS affects people around the world, it is most prevalent in Newfoundland and within the Bedouin population in Kuwait. Genetic researchers have identified variations in approximately 15 genes that can cause the disorder.

BBS appears to impair the function of cilia, tiny hair-like structures found in many organs and tissues, including photoreceptors in the retina. Cilia play an essential role in transporting proteins and nutrients that are responsible for normal functioning of a variety of cells and biological systems.

Led by Samuel Wu, Ph.D., Camille and Raymond Hankamer Chair in Ophthalmology at Baylor College of Medicine, the research team injected the treatment underneath the retinas of mice affected by variations in the BBS4 gene. The therapy consisted of a corrective BBS4 gene that was delivered to photoreceptors in the retina by an adeno-associated virus, the same mechanism used in successful gene therapy clinical trials for Leber congenital amaurosis (LCA). The team observed that photoreceptors treated with the BBS gene therapy survived and continued to provide vision while untreated photoreceptors died.

The BBS4 gene plays an important role in facilitating the transport of rhodopsin, a light-absorbing protein essential for vision, to the outer segments of photoreceptors. When BBS4 is defective, rhodopsin doesn’t reach the outer segments, and as a result, vision is lost and photoreceptors degenerate.

“We are very pleased with this advancement, because it holds promise for preserving vision for people affected by an extraordinarily challenging condition. We are delighted to have a treatment option emerging for them,” says Stephen Rose, Ph.D., chief research officer, Foundation Fighting Blindness. “Furthermore, it is great to see the research community leveraging the success of our landmark gene therapy trials for Leber congenital amaurosis. This is just one of many examples of how the LCA work is opening the door to treat a variety of retinal degenerative diseases.”

William Hauswirth, Rybaczki-Bullard Professor of Ophthalmology and Molecular Genetics at the University of Florida, College of Medicine, provided the AAV used in the BBS study.

David Simons, an investigator on the BBS gene therapy project, says that the team’s work has strong clinical potential. “It is a little early to predict when this treatment would be ready for a clinical trial. There’s more work to be done. But this is a huge step forward,” he says. “Our success also opens the door for treating Bardet-Biedl syndrome caused by other genetic variations.”

Results of the study were published in an early edition of the journal Proceedings of the National Academy of Sciences, March 28, 2011.

 

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