Whole exome sequencing of extreme age-related macular degeneration phenotypes.

PURPOSE: Demographic, environmental, and genetic risk factors for age-related macular degeneration (AMD) have been identified; however, a substantial portion of the variance in AMD disease risk and heritability remains unexplained. To identify AMD risk variants and generate hypotheses for future studies, we performed whole exome sequencing for 75 individuals whose phenotype was not well predicted by their genotype at known risk loci. We hypothesized that these phenotypically extreme individuals were more likely to carry rare risk or protective variants with large effect sizes. METHODS: A genetic risk score was calculated in a case-control set of 864 individuals (467 AMD cases, 397 controls) based on 19 common (≥1% minor allele frequency, MAF) single nucleotide variants previously associated with the risk of advanced AMD in a large meta-analysis of advanced cases and controls. We then selected for sequencing 39 cases with bilateral choroidal neovascularization with the lowest genetic risk scores to detect risk variants and 36 unaffected controls with the highest genetic risk score to detect protective variants. After minimizing the influence of 19 common genetic risk loci on case-control status, we targeted single variants of large effect and the aggregate effect of weaker variants within genes and pathways. Single variant tests were conducted on all variants, while gene-based and pathway analyses were conducted on three subsets of data: 1) rare (≤1% MAF in the European population) stop, splice, or damaging missense variants, 2) all rare variants, and 3) all variants. All analyses controlled for the effects of age and sex. RESULTS: No variant, gene, or pathway outside regions known to be associated with risk for advanced AMD reached genome-wide significance. However, we identified several variants with substantial differences in allele frequency between cases and controls with strong additive effects on affection status after controlling for age and sex. Protective effects trending toward significance were detected at two loci identified in single-variant analyses: an intronic variant in FBLN7 (the gene encoding fibulin 7) and at three variants near pyridoxal (pyridoxine, vitamin B6) kinase (PDXK). Aggregate rare-variant analyses suggested evidence for association at ASRGL1, a gene previously linked to photoreceptor cell death, and at BSDC1. In known AMD loci we also identified 29 novel or rare damaging missense or stop/splice variants in our sample of cases and controls. CONCLUSIONS: Identified variants and genes may highlight regions important in the pathogenesis of AMD and are key targets for replication.

Genetic factors in nonsmokers with age-related macular degeneration revealed through genome-wide gene-environment interaction analysis.

Relatively little is known about the interaction between genes and environment in the complex etiology of age-related macular degeneration (AMD). This study aimed to identify novel factors associated with AMD by analyzing gene-smoking interactions in a genome-wide association study of 1207 AMD cases and 686 controls of Caucasian background with genotype data on 668,238 single nucleotide polymorphisms (SNPs) after quality control. Participants' history of smoking at least 100 cigarettes lifetime was determined by a self-administered questionnaire. SNP associations modeled the effect of the minor allele additively on AMD using logistic regression, with adjustment for age, sex, and ever/never smoking. Joint effects of SNPs and smoking were examined comparing a null model containing only age, sex, and smoking against an extended model including genotypic and interaction terms. Genome-wide significant main effects were detected at three known AMD loci: CFH (P = 7.51×10(-30) ), ARMS2 (P = 1.94×10(-23) ), and RDBP/CFB/C2 (P = 4.37×10(-10) ), while joint effects analysis revealed three genomic regions with P < 10(-5) . Analyses stratified by smoking found genetic associations largely restricted to nonsmokers, with one notable exception: the chromosome 18q22.1 intergenic SNP rs17073641 (between SERPINB8 and CDH7), more strongly associated in nonsmokers (OR = 0.57, P = 2.73 × 10(-5) ), with an inverse association among smokers (OR = 1.42, P = 0.00228), suggesting that smoking modifies the effect of some genetic polymorphisms on AMD risk.

Mitochondrial haplogroup X is associated with successful aging in the Amish.

Avoiding disease, maintaining physical and cognitive function, and continued social engagement in long-lived individuals describe successful aging (SA). Mitochondrial lineages described by patterns of common genetic variants ("haplogroups") have been associated with increased longevity in different populations. We investigated the influence of mitochondrial haplogroups on SA in an Amish community sample. Cognitively intact volunteers aged ≥80 years (n = 261) were enrolled in a door-to-door survey of Amish communities in Indiana and Ohio. Individuals scoring in the top third for lower extremity function, needing little assistance with self-care tasks, having no depression symptoms, and expressing high life satisfaction were considered SA (n = 74). The remainder (n = 187) were retained as controls. These individuals descend from 51 matrilines in a single 13-generation pedigree. Mitochondrial haplogroups were assigned using the ten mitochondrial single nucleotide polymorphisms (mtSNPs) defining the nine most common European haplogroups. An additional 17 mtSNPs from a genome-wide association panel were also investigated. Associations between haplogroups, mtSNPs, and SA were determined by logistic regression models accounting for sex, age, body mass index, and matriline via generalized estimating equations. SA cases were more likely to carry Haplogroup X (OR = 7.56, p = 0.0015), and less likely to carry Haplogroup J (OR = 0.40, p = 0.0003). Our results represent a novel association of Haplogroup X with SA and suggest that variants in the mitochondrial genome may promote maintenance of both physical and cognitive function in older adults.

Set-based joint test of interaction between SNPs in the VEGF pathway and exogenous estrogen finds association with age-related macular degeneration.

Purpose:Age-Related Macular Degeneration (AMD) is the leading cause of irreversible visual loss in developed countries. Its etiology includes genetic and environmental factors. Although VEGFA variants are associated with AMD, the joint action of variants within the VEGF pathway and their interaction with non-genetic factors has not been investigated. Methods:Affymetrix 6.0 chipsets were used to genotype 668,238 SNPs in 1,207 AMD cases and 686 controls. Environmental exposures were collected by questionnaire. A set-based test was conducted using the chi-square statistic at each SNP derived from Kraft's 2df joint test. Pathway and gene-based test statistics were calculated as the mean of all independent SNP statistics. Phenotype labels were permuted 10,000 times to generate an empirical p-value. Results: While a main effect of the VEGF pathway was not identified, the pathway was associated with neovascular AMD in women when accounting for birth control pill (BCP) use (P= 0.017). Analysis of VEGF's subpathways found that SNPs in the Proliferation subpathway were associated with neovascular AMD (P=0.029) when accounting for BCP use. Nominally significant genes within this subpathway were also observed. Stratification by BCP use revealed novel significant genetic effects in women who had taken BCPs. Conclusions: These results illustrate that some AMD genetic risk factors may only be revealed when considering complex relationships among risk factors. This shows the utility of exploring pathways of previously associated genes to find novel effects. It also demonstrates the importance of incorporating environmental exposures in tests of genetic association at the SNP, gene, or pathway level.