Age-related macular degeneration (AMD) is the most frequent cause of irreversible blindness in the elderly in developed countries. Our previous studies implicated activation of complement in the formation of drusen, the hallmark lesion of AMD. Here, we show that factor H (HF1), the major inhibitor of the alternative complement pathway, accumulates within drusen and is synthesized by the retinal pigmented epithelium. Because previous linkage analyses identified chromosome 1q25-32, which harbors the factor H gene (HF1͞CFH), as an AMD susceptibility locus, we analyzed HF1 for genetic variation in two independent cohorts comprised of Ϸ900 AMD cases and 400 matched controls. We found association of eight common HF1 SNPs with AMD; two common missense variants exhibit highly significant associations (I62V, 2 ‫؍‬ 26.1 and P ‫؍‬ 3.2 ؋ 10 ؊7 and Y402H, 2 ‫؍‬ 54.4 and P ‫؍‬ 1.6 ؋ 10 ؊13 ). Haplotype analysis reveals that multiple HF1 variants confer elevated or reduced risk of AMD. One common at-risk haplotype is present at a frequency of 50% in AMD cases and 29% in controls [odds ratio (OR) ‫؍‬ 2.46, 95% confidence interval (1.95-3.11)]. Homozygotes for this haplotype account for 24% of cases and 8% of controls [OR ‫؍‬ 3.51, 95% confidence interval (2.13-5.78)]. Several protective haplotypes are also identified (OR ‫؍‬ 0.44 -0.55), further implicating HF1 function in the pathogenetic mechanisms underlying AMD. We propose that genetic variation in a regulator of the alternative complement pathway, when combined with a triggering event, such as infection, underlie a major proportion of AMD in the human population.A ge-related macular degeneration (AMD) is the leading cause of irreversible vision loss (1, 2), affecting Ϸ50 million individuals worldwide. AMD is characterized by a progressive loss of central vision attributable to degenerative and neovascular changes that occur at the interface between the neural retina and the underlying choroid. At this location are the retinal photoreceptors, the retinal pigmented epithelium (RPE), a basement membrane complex known as Bruch's membrane (BM) and a network of choroidal capillaries.The prevailing view is that AMD is a complex disorder stemming from the interaction of multiple genetic and environmental risk factors (3,4). Familial aggregation studies indicate that a genetic contribution can be identified in up to 25% of the cases (5). Thus, AMD appears to be a product of the interaction between multiple susceptibility loci rather than a collection of single-gene disorders. The number of loci involved, the attributable risk conferred, and the interactions between various loci remain obscure.

Age-related macular degeneration (AMD) is the most common form of irreversible blindness in developed countries 1,2 . Variants in the factor H gene (CFH, also known as HF1), which encodes a major inhibitor of the alternative complement pathway, are associated with the risk for developing AMD [3][4][5][6][7][8] . Here we test the hypothesis that variation in genes encoding other regulatory proteins of the same pathway is associated with AMD. We screened factor B (BF) and complement component 2 (C2) genes, located in the major histo-compatibility complex class III region, for genetic variation in two independent cohorts comprising ~900 individuals with AMD and ~400 matched controls. Haplotype analyses identify a statistically significant common risk haplotype (H1) and two protective haplotypes. The L9H variant of BF and the E318D variant of C2 (H10), as well as a variant in intron 10 of C2 and the R32Q variant of BF (H7), confer a significantly reduced risk of AMD (odds ratio = 0. 45 and 0.36, respectively). Combined analysis of the C2 and BF haplotypes and CFH variants shows that variation in the two loci can predict the clinical outcome in 74% of the affected individuals and 56% of the controls. These data expand and refine our understanding of the genetic risk for AMD.Correspondence should be addressed to R.A. (rla22@columbia.edu) or M.D. (dean@ncifcrf.gov). Note: Supplementary information is available on the Nature Genetics website. AUTHOR CONTRIBUTION STATEMENTThe AMD Genetics Clinical Study Group includes Stanley Chang, Lawrence A. Yannuzzi, John C. Merriam and Irene Barbazetto (Department of Ophthalmology, Columbia University, New York); Leonid E. Lerner (F.M. Kirby Center for Molecular Ophthalmology, Scheie Eye Institute, University of Pennsylvania School of Medicine, Philadelphia) and Stephen Russell, Jamal Hoballah, Jill Hageman and Heather Stockman (Department of Ophthalmology and Visual Sciences, Center for Macular Degeneration, University of Iowa, Iowa City, Iowa, USA). COMPETING INTERESTS STATEMENTThe authors declare competing financial interests (see the Nature Genetics website for details).Reprints and permissions information is available online at http://npg.nature.com/reprintsandpermissions/ NIH Public Access Inflammation has a central role in the pathobiology of AMD 9-14 . Dysfunction of the complement pathway is proposed to induce significant damage to macular cells, leading to atrophy, degeneration and the elaboration of choroidal neovascular membranes 3,[15][16][17] . Activation of the alternative pathway is initiated by cleavage of C3b-bound factor B (BF), resulting in the formation of the C3Bb complex (C3 convertase). This complex is stabilized by properdin, whereas its dissociation is accelerated by regulatory proteins, including complement factor H (CFH), the major inhibitor of the alternative complement pathway. As CFH haplotypes are associated with AMD 3 , we hypothesized that the same may be true for activators of the same pathway, such as complement factor B (BF). BF and compl...