Gene Therapy: How a New Cure for Blindness Reverses Retinal Dystrophy

A new gene therapy called Luxturna was being considered by the FDA on Thursday to treat retinal dystrophy, which can lead to blindness. If approved, it would be the first-ever gene replacement therapy. KAREN BLEIER/AFP/Getty Images

Updated | A Food and Drug Administration committee has voted that a gene therapy touted as a breakthrough for people with a particular genetic form of blindness is effective. A final FDA approval for the treatment, Luxturna, would be a landmark event for gene therapy and for sufferers of this inherited disorder.

Whether this is the first gene therapy to get this close to FDA approval depends on your definition of "gene therapy." The term can be broadly defined as treatments that use genes in some way. In theory, diseases could be cured or prevented by stopping one gene from being expressed, replacing a gene that causes a disease with one that doesn't, or by taking a bad gene out and putting in a good gene.

More precisely, Luxturna is a gene replacement therapy, Stephen Rose tells Newsweek. Rose is the chief scientific officer of the Foundation Fighting Blindness, which funded some of the preliminary research on the therapy.

"It's a proof of principle for gene replacement for all sorts of other inherited rare retinal degenerations," Rose says.

Gene replacement therapy is not gene editing. The treatment does not erase the mutation that causes a disease, but it does put copies of the normal gene into cells so they can work properly.

In this case, the gene therapy treats a condition called retinal dystrophy. There are actually many kinds of retinal dystrophies, including Leber congenital amaurosis and retinitis pigmentosa. Some can be caused by a mutation in a gene called RPE-65.

"The RPE-65 gene produces the gasoline that the retina needs in order to function," Rose says, comparing the retina to a car. "So what happens is that the engine hasn't even turned on. Those cells are being starved, and they're going to die. But they don't die immediately. They're like a hybrid engine. They're stopped, but not turned off."

The gene therapy allows the retina to start producing the "gasoline" it needs, which allows the cells to send the signals to the brain. Those signals are how humans see.

People with these conditions should only need to be treated with the therapy once, Rose says. Unlike drugs, genes aren't broken down in the body. Instead, the retinal cells will use the genes like templates to produce the necessary proteins. They should never be destroyed in the process.

The virus used to get the gene into the eye in the first place is called an adeno-associated virus (AAV). This kind of virus doesn't cause disease in humans—in fact, most people already have some in their body.

AAVs are not the same kind of virus that was used in the first attempt at a gene therapy decades ago. In 1999, Jesse Gelsinger died after being treated with a gene therapy using an adenovirus for a condition that affected his liver.

But this gene therapy is different in many ways from the one Gelsinger tried, Rose says. "We have a different type of virus than Jesse Gelsinger received; we're not doing it systematically, we're using a virus that doesn't cause disease, and with these different serotypes, we can target different cells within the retina."

The FDA had some questions before the treatment can be approved, which a panel of experts asked on Thursday. Many of their questions were expected to center around the validity of tests used in clinical trials, the age at which patients could be treated and the likelihood that people might need more than one treatment.

The panel voted 16-0 that the treatment benefits seemed to outweigh the risks. Though not binding, this vote was important; the FDA often follows the advice of the committee when it considers whether to approve a drug.

The FDA must make its final decision before January 12.

This article has been updated to include the results of the FDA commitee's vote.