Seeing eye dogs
Leber congenital amaurosis (LCA) is a rare, inherited genetic disease that causes nearly total blindness in infancy. There is currently no treatment for the disease but LCA (and retinal degeneration in general) is a good candidate for gene therapy because the photoreceptor cells, which are typically affected, are relatively intact (in the short term) and accessible to injected agents. Most efforts have been focused on trying to slow retinal degeneration and eventual blindness in mice and rats. But, the restoration of sight to a blind eye has not been demonstrated-in rodents or any animal-until now. A team of scientists headed by Jean Bennett (of University of Pennsylvania, Philadelphia, USA) describes the first successful gene therapy that restores sight in blind dogs (Nature Genetics, Vol. 28, No. 1, 01 May 2001).
Mutations in at least three known genes can cause LCA. One gene, RPE65, encodes a protein that is involved in metabolizing retinoids to form retinal, the chromophore of the visual pigments in the photoreceptor cells. (These are responsible for 'translating' light into nerve impulses.) Mice with mutations in Rpe65 have nonfunctional photoreceptors and retinas that degrade over time.
Bennett and colleagues studied dogs that have a naturally occurring mutation in RPE65 and go blind or develop impaired vision, much the same way infants with LCA do. They used a common viral-based gene therapy vector to deliver a normal copy of RPE65 to the retinas of a cohort of these dogs. Following treatment, measurements of vision, such as sensitivity to electrophysiological stimuli, indicated that the eye that received treatment responded as well as eyes of seeing dogs. They also tested the treated animals for different behavioral tasks, such as the ability to avoid obstacles in dim light. As revealed by the supporting video (posted on the press web site) the dogs avoided bumping into objects placed on the same side as the treated eye.
This study provides hope that, despite the numerous and substantive obstacles to developing effective gene therapy, the correction of LCA arising from mutations in RPE65 is at least feasible.
Dr. Jean Bennett
University of Pennsylvania School of Medicine
Philadelphia, Pennsylvania - USA
Telephone: +1 215-898-0915
Fax: +1 215-573-7155
Dr. Inder Verma
The Salk Institute
La Jolla, California - USA
Telephone: +1 858-453-4100 x1462
Fax: +1 858-558-7454
(C) Nature Genetics press release.
Message posted by: Trevor M. D'Souza