Complement factor H polymorphism, complement activators, and risk of age-related macular degeneration

Abstract

Context: The evidence that inflammation is an important pathway in age-related macular degeneration (AMD) is growing. Recent case-control studies demonstrated an association between the complement factor H (CFH) gene, a regulator of complement, and AMD.

Objectives: To assess the associations between the CFH gene and AMD in the general population and to investigate the modifying effect of smoking, serum inflammatory markers, and genetic variation of C-reactive protein (CRP).

Design, setting, and participants: Population-based, prospective cohort study of individuals aged 55 years or older (enrollment between March 20, 1990, and July 31, 1993, and 3 follow-up examinations that were performed between September 1, 1993, and December 31, 2004) in Rotterdam, the Netherlands. The CFH Y402H polymorphism was determined in a total of 5681 individuals. Information on smoking, erythrocyte sedimentation rate, CRP serum levels, and haplotypes of the CRP gene were assessed at baseline.

Main outcome measures: All severity stages of prevalent and incident AMD, graded according to the international classification and grading system for AMD.

Results: The frequency of CFH Y402H was 36.2% (4116/11,362 alleles). At baseline, there were 2062 persons (36.3%) with any type of AMD (prevalent cases), including 78 (1.4%) with late AMD (stage 4). During follow-up (mean, 8 years; median, 10 years), 1649 (35.5%) of 4642 participants progressed to a higher stage of AMD (incident cases), including 93 (5.6%) who developed late AMD. The odds ratio (OR) of AMD increased in an allele-dose manner with 2.00 (95% confidence interval [CI], 1.56-2.55) for stage 2 AMD, 4.58 (95% CI, 2.82-7.44) for stage 3 AMD, and 11.02 (95% CI, 6.82-11.81) for stage 4 (late, vision threatening) AMD for homozygous persons. Cumulative risks calculated by Kaplan-Meier analysis of late AMD by age 95 years were 48.3% for homozygotes, 42.6% for heterozygotes, and 21.9% for noncarriers. The population-attributable risk for CFH Y402H was 54.0%. Elevated erythrocyte sedimentation rates further increased the OR to 20.2 (95% CI, 9.5-43.0), elevated serum CRP levels to 27.7 (95% CI, 10.7-72.0), and smoking to 34.0 (95% CI, 13.0-88.6) for homozygotes compared with noncarriers without these determinants. The CRP haplotypes conferring high levels of CRP significantly increased the effect of CFH Y402H (P<.01).

Conclusions: The CFH Y402H polymorphism may account for a substantial proportion of AMD in individuals similar to those in the Rotterdam Study and may confer particular risk in the presence of environmental and genetic stimulators of the complement cascade.