Norrie disease is an X-linked genetic disorder characterized by progressive atrophy of the eyes, mental disturbances and deafness. The gene responsible for this disease was initially identified through positional cloning. Norrin, the gene product, encodes a small secreted, cysteine-rich protein that is thought to act as a ligand for the Wnt-receptor/beta-catenin signal pathway despite having sequence homology with the Wnt family of proteins. Mice lacking this gene have abnormal blood vessel growth in the vitreous and a disorganized retina; transgenic ectopic expression of Norrin restores normal retinal vasculature. Recent evidence shows that Norrin can attenuate tPA and uPA-mediated death of transformed rat retinal ganglion cells (RGC-5) by activating the Wnt/beta-catenin pathway and regulating the phosphorylation of LRP-1, a cell surface receptor for tPA and uPA, suggesting the Norrin may function in vivo by regulating kinases which may alter the phosphorylation of LRP-1.