Genetic reactivation of cone photoreceptors restores visual responses in retinitis pigmentosa

Let There Be Light Retinitis pigmentosa, a disease that can result from a wide variety of genetic defects, causes degeneration of photoreceptor cells in the retina and leads to blindness. In the course of the disease, it is generally the rod photoreceptor cells that degenerate first. Cone photoreceptor cells may persist, but in a damaged and nonfunctional state. Busskamp et al. (p. 413 , published online 24 June; see the cover; see the Perspective by Cepko ) have now applied a gene therapy approach to mouse models of retinitis pigmentosa. Inducing expression of a bacterial light-activated ion pump, halorho dopsin, in the damaged cone cells improved visual responses in the diseased mouse retinas. Thus, it may be possible to rescue cone photoreceptors therapeutically, even after they have already been damaged.