X-LINKED RETINOSCHISIS ELECTROPHYSIOLOGY, MOLECULAR GENETICS AND TREATMENT

Abstract: X-linked retinoschisis (XLRS) is a congenital progressive inherited retinal disease that affects the entire retina and is one of the more common causes of vision loss from retinal degeneration affecting young men,. The progression is variable but seems to be relatively stationary in the ages 6 to 25 years. Patients with XLRS lack a functional retinoschisin protein in the eye, because of mutation in the RS1 gene, and are more prone to retinal detachment compared to the general population. To explore the influence of RS1-protein in human retinal detachment, we compared, vitreal RS1 protein levels in eyes with or without detachment and found altered levels. This finding demonstrates a possible role of RS1 protein in retinal detachment and may be of interest in the choice of surgical technique for the treatment of retinal detachment. We generated a mouse model, Rs1-KO, deficient in Rs1 gene, to determine the role of RS1 protein, retinoschisin, in retinal structure and function. The knockout mouse mimics structural features of human X-linked juvenile retinoschisis with progressive rod and cone degeneration, cystic dissection through, and disorganization of, multiple retinal layers. The Rs1-KO mouse functional deficit results in an electronegative ERG waveform that is characteristic of human retinoschisis disease and that implicates a synaptic transmission deficit in the absence of retinoschisin protein. To explore the viable use of gene replacement therapy as treatment for XLRS, we delivered an AAV serotype 2 vector containing the mouse Rs1 cDNA under the control of CMV promoter AAV(2/2)-CMV-Rs1 into the vitreous space in the Rs1-KO mice. A few months after delivery, we saw staining of retinoschisin in all retinal layers of Rs1-KO mice including an intense staining in the photoreceptors inner segment mimicking retinoschisin distribution in WT retina. The electroretinography recordings showed reversal of the electronegative waveform and restoration of the normal positive b-wave. In paper II, we treated the mice at an earlier time point, 14 days, and followed them out to 14 months. We demonstrated both structural and functional long term rescue in the Rs1-KO mouse retina. We also studied the effect of transient subretinal detachments and conclude that large short-term detachments in Rs1-KO mice, followed by a period of reattachment may cause a slight increase in photoreceptor cell death, but detachments do not accentuate the gliosis and neurite sprouting. These findings suggest that performing subretinal injections to deliver therapeutic agents may be a viable option in the treatment of patients with x-linked retinoschisis without causing significant cellular damage to the retina but may be problematic for other reasons e.g. only small geographically delivery of the RS1 gene. This thesis signifies that gene replacement therapy through intravitreal delivery is a feasible strategy of therapeutic intervention both early and in the post-developmental adult stage of XLRS disease