Stargardt-like macular dystrophy (STGD3, MIM 600110) is an autosomal dominant form of juvenile macular degeneration characterized by decreased visual acuity, macular atrophy, and extensive flecks. Using a positional cloning approach, we identified ELOVL4 as the causal disease gene responsible for Stargardt-like macular dystrophy (STGD3, MIM 600110). ELOVL4 encodes a protein with sequence and structural similarities to the ELO family of proteins. The ELO family of proteins is involved in the elongation of long chain fatty acids (LCFA), suggesting that ELOVL4 may have a similar function. The long term objectives of this proposal are to characterize the biochemical properties of ELOVL4 and to elucidate molecular mechanism leading to macular degeneration due to ELOVL4 mutations in humans. ELOVL4 proteins are strongly conserved throughout vertebrate species. The exact enzymatic function of ELOVL4 and the pathogenic mechanisms by which mutant ELOVL4 causes macular degeneration are unclear. Our central hypothesis is that ELOVL4 is a key enzyme in a biosynthetic pathway that produces very long chain fatty acids which play an essential rolejn retina development and function. Guided by this hypothesis, we propose to define ELOVL4 function through a comprehensive analysis of fatty acid composition in vitro and in vivo, and to examine retinal development and pathogenesis in ELOVL4 transgenic, knockin, and knockout mice. To further understand ELOVL4 functions and pathogenic mechanisms giving rise to macular degeneration we will address the following specific aims: Specific Aim 1: To determine the enzymatic function of ELOVL4 Specific Aim 2: To determine the role of ELOVL4 in retinal development and pathology . Specific Aim 3: To examine RPE dysfunction in ELOVL4 mutant transgenic mice Stargardt macular dystrophy is the most common juvenile macular degeneration and shares many important clinical and histopathological similarities with AMD including an abnormal accumulation of lipofuscin in the RPE, atrophy of the RPE and overlying photoreceptor cells, and loss of central vision. ELOVL4 is the first gene involved in the biosynthesis of long chain fatty acids implicated in any form of macular degeneration. The proposed study should lead to new insights into lipid metabolism in photoreceptor cells and reveal a novel pathway in the pathogenesis of macular degeneration. Our study should also provide insights into the formation of lipofuscin and provide new avenues for treatments for Stargardt macular dystrophy and AMD.