gms | German Medical Science

Since the first discovery of a gene causing retinitis pigmentosa in 1980, there has been remarkable progress by many investigators to identify the causative genes for most forms of inherited blinding diseases of the retina. It is estimated that all of the causative genes for most large patient groups and families are now known, with only a small number of very rare cases yet to be elucidated. Currently there are over 250 gene defects identified, making blindness one of the most heterogeneous diseases known. With this great amount of molecular information now available, common, causative mechanisms and defects in biochemical pathways are beginning to emerge. An unforeseen finding is that the great majority of the identified genes (over 95%) specifically cause death of rod photoreceptors. Only a handful of the identified genes are expressed in retinal glia, retinal interneurons, ganglion cells or the retinal pigment epithelium. This implies that cone photoreceptors, responsible for high-resolution and color vision, are genetically normal in most patients, but degenerate as a consequence of the death of rod photoreceptors. We describe a molecular mechanism by which the rod-derived cone viability factor (RdCVF), a factor normally released by rods, controls glucose entry into cones, enhancing their survival. Rods cell death deprives cones of this necessary factor, and cones literally starve to death. Virus mediated gene transfer of RdCVF to the retina, can dramatically slow cone loss and increase their physiologic function by supplying this secreted factor from other cellular sources. This may be a broadly applicable treatment for many retinal degeneration patients, as it does not require knowledge of the causative mutation. This type of therapy is far from perfect, as it does nothing to prevent rods from degeneration, but may be useful to save genetically healthy cones in retinal dystrophies.