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.

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