Association of age-related macular degeneration with complement activation products, smoking, and single nucleotide polymorphisms in South Carolinians of European and African descent

Abstract

Purpose: Smoking and the incidence of age-related macular degeneration (AMD) have been linked to an overactive complement system. Here, we examined in a retrospective cohort study whether AMD-associated single nucleotide polymorphisms (SNPs), smoking, ethnicity, and disease status are correlated with blood complement levels.

Methods: Population: The study involved 91 AMD patients and 133 controls, which included 73% Americans of European descent (EUR) and 27% Americans of African descent (AFR) in South Carolina. Readouts: Participants were genotyped for 10 SNPs and systemic levels of complement factor H (CFH) activity, and the complement activation products C3a, C5a, and Bb were assessed. Main Outcome Measures: Univariate and multivariable logistic regression models were used to examine associations between AMD status and distinct readouts.

Results: AMD affects EUR individuals more than AFRs. EUR but not AFR AMD subjects revealed higher levels of Factors C3a and Bb. In all subjects, a 10-unit increase in C3a levels was associated with an approximately 10% increase in the odds of being AMD-positive, and C3a and Bb were associated with smoking. While CFH activity levels were not correlated with AMD, a significant interaction was evident between patient age and CFH activity. Finally, EURs had lower odds of AMD with enhanced copies of rs1536304 (VEGFA) and higher odds with more copy numbers of rs3766404 (CFH).

Conclusions: Our results support previous studies of systemic complement components being potential biomarkers for AMD, but they suggest that smoking and disease do not synergistically affect complement levels. We also suggest a novel susceptibility and protective haplotypes in the South Carolinian AMD population. Our studies indicate that augmented complement activation associated with advanced AMD could be attributed to a decrease in CFH activity in younger patients.

Figure 1

Plot of the OR for a ten-year increase in age with increasing levels of the inhibition of alternative pathway-mediated lysis by factor H. Percent inhibition of lysis has been normalized to 100 as described in the methods. The solid line is the OR from the multiple logistic regression model of AMD presented in Table 3. The dashed lines represent the 95% confidence interval for the OR at specific values of the inhibition of lysis. The solid gray line represents the null OR of 1. Values of the inhibition of lysis range from 50 to 175, which are the 10th and 90th percentiles of observed values in our study population. The plot indicates that as the inhibition of lysis increases, the impact of increasing age on the probability of developing AMD decreases.

Figure 2

Association between advanced AMD and common SNPs in EURs and AFRs. A forest plot of the univariate association between advanced AMD and common SNPs in A: EURs and B: AFRs. The table describes the SNP being considered, the model type, the estimated OR for AMD, and the associated p value. The plot shows the estimated OR with 95% CIs for the respective SNP and model. The gray vertical line represents the null OR of 1. Recessive SNP models missing values in the table and on the plot indicate that there were fewer than three subjects in the study population with two copies of the minor allele for that SNP. Additive models with missing values indicate that no subjects were recessive for the minor allele.

Figure 3

Association between complement levels and SNPs across all subjects. A forest plot of the association between complement levels and SNPs by race (EUR or AFR). The table describes the SNP and complement factor being considered, the SNP model type, the estimated difference in mean complement levels by SNP status, and the associated p value. The plot shows the estimated mean difference in complement levels with 95% CIs for the respective SNP and model. The gray vertical line represents a null mean difference of 0. Recessive SNP models missing values in the table and on the plot indicate that there were fewer than three subjects in the study population with two copies of the minor allele for that SNP. Additive models with missing values indicate that no subjects were recessive for the minor allele.