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Researchers studying the genetics of age related macular degeneration have found a link with a polymorphism in the gene encoding C3, the most abundant of the 30 or so proteins that make up the complement system. In three case-control cohorts from England and Scotland the polymorphism was significantly associated with severe, sight threatening forms of the disease—geographic atrophy and choroidal neovascularisation. Two other polymorphisms in complement genes have already been linked to this disease, suggesting a central role for inflammation in the pathogenesis of age related macular degeneration.
In this study, subjects with the F (denoting “fast”) allele of the C3 gene were more susceptible than those with the S (“slow”) allele. People with two copies of the F allele had more than twice the odds of serious disease than those with two copies of the S allele (odds ratio 2.6, 95% CI 1.6 to 4.1 for FF homozygotes versus SS homozygotes). But even heterozygotes for the F allele had increased risk (1.7, 1.3 to 2.1).
The researchers estimate that 22% of age related macular degeneration in white Europeans could be due to this polymorphism.