Improved Cone Function Following Gene Therapy in a Mouse Model of Leber Congenital Amaurosis (LCA) Caused by RetGC Deficiency

Abstract

Purpose: : Retinal guanylate cyclase (RetGC), encoded by GUCY2D, replenishes depleted cGMP during dark state restoration in photoreceptors. Loss-of-function mutations in GUCY2D cause 15-20 % of LCA. The aim of this study was to test the efficacy of gene replacement therapy in a RetGC knock-out mouse.

Methods: : Scotopic and photopic electroretinograms (ERGs) were used to test photoreceptor function. The human GUCY2D gene driven by the rhodopsin kinase promoter was cloned into a recombinant adeno-associated virus (rAAV2/8) vector and delivered using subretinal injections to P10 RetGC knock-out mice.

Results: : In animals treated with vector alone, scotopic ERGs appear to improve at 2 weeks post injection, but differences were only evident at high flash intensities. Photopic flash and flicker ERGs did not improve until 4 weeks post injection when a b-wave becomes evident in treated eyes whereas in untreated eyes there is a flat ERG. Photopic b-waves improve over the next 2 weeks and stabilise at 6 weeks, but do not reach wild type levels. ERG and histological analysis is ongoing.

Conclusions: : We have achieved for the first time improved retinal function following gene replacement therapy in a murine model of LCA caused by RetGC deficiency.

Keywords: gene transfer/gene therapy • photoreceptors • transgenics/knock-outs