Visual impairments affect over 160 million people worldwide, and of these, roughly 37 million are blind (1). Major causes of blindness include cataracts, glaucoma, retinitis pigmentosa and age-related macular degeneration and the development of effective, low-cost therapies for these disorders is of the highest priority. Model organisms with similar anatomy and physiology to humans are vital to understand the molecular and cellular mechanisms underlying these diseases and in which to develop and test potential therapies. The zebrafish, Danio rerio, is an ideal system for modeling human disease, and studies utilizing zebrafish to elucidate the molecular and cellular underpinnings of congenital ocular disorders have made a significant impact in the field. Indeed, the combination of forward genetic screens to identify zebrafish mutants with ocular defects, and the rapid pace of technological advancement in analyzing the mutant phenotypes has positioned the zebrafish system at the forefront of those that contribute to our knowledge of the mechanistic underpinnings of human congenital eye diseases. Research in this grant will utilize an innovative whole-genome sequencing and SNP mapping approach to rapidly and affordably clone recessive zebrafish visual system mutants identified from a recently completed forward genetic screen in our lab. 23 mutants were identified in our screen that presented with congenital cataracts, anterior segment dysgenesis, colobomas, oculocutaneous albinism, retinal degeneration and other developmental defects. Our novel mapping technique will enable us to clone the affected loci in most, if not all, of these mutants and then perform targeted, hypothesis-driven experiments to determine the underlying molecular and cellular mechanisms that lead to ocular defects. We will focus these further research efforts on the congenital cataract mutants. Congenital cataracts occur in ~40 per 100,000 human births and represent the most common cause of childhood blindness in the developed world. Cataracts are also a common clinical feature in nearly 200 different human genetic diseases making them a frequent component of an otherwise heterogeneous collection of disorders. While much is known about age-related and environmentally induced cataracts, less is known about the etiology of congenital cataracts. Thus, the studies proposed here will have significant scientific merit as they will identify gene products required for normal lens development and they will provide animal congenital cataract models through which an understanding of disease mechanism can be can be advanced and a model through which novel therapies can be developed and tested.