Today, the an FDA advisory committee recommended that the FDA approve full clinical trials for a type of gene therapy that addresses a rare genetic condition causing deterioration of the retina. This is found in 8.6×105 of people world wide, so not many. the therapy involves injecting a virus bearing the preferred copy of the gene, the non-broken allele, into the eyeball, where the new gene somehow reduces, stops, and seemingly reverses, the deterioration.
The therapy was previously looked at in a preliminary study with a small sample of people. Here is the abstract from that study:
RPE65: Role in the visual cycle, human retinal disease, and gene therapy b Cai et al, 2009.
RPE65 is an isomerohydrolase expressed in retinal pigment epithelium. It is critical for the regeneration of the visual pigment necessary for both rod and cone-mediated vision. Mutations in human RPE65 cause Leber’s congenital amaurosis and other forms of autosomal recessive retinitis pigmentosa which are associated with early-onset blindness. Several RPE65 animal models including two different mouse models and a naturally occurring canine model have been thoroughly characterized to determine the mechanisms that underlie RPE65 associated retinal dystrophies. More recently, substantial effort has gone into designing gene therapies for these diseases. Based on several encouraging reports from animal models, at least three clinical trials are currently underway for the treatment of LCA using modified AAV vectors carrying the RPE65 cDNA and have reported positive preliminary results.
The preliminary study leading to the recommendation of full trials had two serious side effects of the injection, and no apparent side effects of the therapy itself, and patients responded to varying but always positive degrees. Some individuals went from legally blind to not legally blind. The patients have been followed for at least three years (up to about five) and no patient’s improvements have reversed.
I do not know why the therapy was developed for a disease almost no one has. I assume there have been parallel efforts to work on more common but similar eye conditions (retinal deterioration of some kind owing to a faulty allele). That is just a guess, but it suggests to me that we should be cautious in our celebration. they got the therapy to work with this one disease.
There have been very few reasonable successes with gene therapy. This is about the fifth positive story so far, all told. But we may be passing a kind of threshold, since all of the successes have emerged just in the last year.
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