Variations in five genes and the severity of age-related macular degeneration: results from the Muenster aging and retina study

Genetic variants and haplotypes in fibulin-5 (FBLN5) are associated with pseudoexfoliation glaucoma but not with pseudoexfoliation syndrome

Pseudoexfoliation (PEX) is a multifactorial age-related disease involving deposition of extracellular proteinaceous aggregates on anterior ocular tissues. The present study aims to identify functional variants in fibulin-5 (FBLN5) as risk factors for the development of PEX. Thirteen tag single-nucleotide polymorphisms (SNPs) in FBLN5 were genotyped using TaqMan SNP genotyping technology to identify association between SNPs of FBLN5 and PEX in an Indian cohort comprising 200 control and 273 PEX patients (169 PEXS and 104 PEXG). Functional analysis of risk variants was done through luciferase reporter assays and electrophoretic mobility shift assay (EMSA) using human lens epithelial cells. Genetic association and risk haplotype analysis showed a significant association of rs17732466:G>A (NC_000014.9:g.91913280G>A) and rs72705342:C>T (NC_000014.9:g.91890855C>T) within FBLN5 as risk factors with the advanced severe stage of the disease, pseudoexfoliation glaucoma (PEXG). Reporter assays showed allele-specific regulatory effect of rs72705342:C>T on gene expression, wherein, construct containing the risk allele showed a significant decrease in the reporter activity compared with the one with protective allele. EMSA further validated higher binding affinity of the risk variant to nuclear protein. In silico analysis predicted binding sites for two transcription factors, GR-α and TFII-I with risk allele at rs72705342:C>T, which were lost in the presence of protective allele. The EMSA showed probable binding of both these proteins to rs72705342. In conclusion, the present study identified the novel association of two genetic variants in FBLN5 with PEXG but not with PEXS, distinguishing between the early and the later forms of PEX. Further, rs72705342:C>T was found to be a functional variant.

Genetic factors associated with age-related macular degeneration: identification of a novel PRPH2 single nucleotide polymorphism associated with increased risk of the disease

PURPOSE

Age-related macular degeneration (AMD) is associated with multiple environmental and genetic risk factors. Two main risk factors for AMD are variants in the CFH and ARMS2/HTRA1 genes. We investigated over 2000 variants in AMD patients and controls using high-throughput sequencing methods to search for variants associated with AMD.

METHODS

A total of 296 AMD patients and 100 controls were enrolled in this study. Genetic analysis was performed with the Illumina NextSeq 500 system.

RESULTS

Multivariate analysis of patients and controls, adjusted for age, sex and smoking status (pack-years), revealed that three SNPs were strong risk factors independently associated with AMD: CFH Y402H, ARMS A69S and PRPH2 c.582-67T>A (rs3818086). The TC genotype in CFH Y402H was associated with 1.90-fold higher odds, and the CC genotype was associated with 5.66-fold higher odds of AMD compared with the TT genotype. The GT genotype in ARMS A69S was associated with 2.40-fold higher odds, and the TT genotype was associated with 6.75-fold higher odds of disease compared with the GG genotype. In the case of rs3818086, the A allele could be considered a 'risk' allele, since AA + TA genotypes were associated with 2.33-fold higher odds of AMD compared with the TT genotype.

CONCLUSIONS

Although PRPH2 mutations have been previously implicated in various forms of retinal degeneration, to the best of our knowledge, this study is the first to show that the rs3818086 variant increases the risk for AMD more than two times. Further studies on larger cohorts are required to elucidate how this variant affects protein structure.

The effect of complement factor B gene variation on age-related macular degeneration in Iranian patients

Purpose

To determine the possible association of rs4151667 (L9H) complement factor B (CFB) gene with age-related macular degeneration (AMD). The L9H is one of the functional variations of the CFB. CFB gene encodes the most important protein of the complement system.

Methods

Two hundred sixty-six patients with AMD and 194 unrelated age/sex-matched controls were genotyped for CFB gene (rs4151667) using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. All research subjects were selected from three regions of Iran (Tehran, Tabriz, and Gonabad).

Results

The results showed a significant difference between the frequency of non-TT genotype in total patients and controls [odds ratio (OR) = 0.424, P = 0.038]. The analysis for each studied region showed that in patients originating from the Gonabad population, the frequency of TT and non-TT genotypes between patients and the control group were significantly different (OR = 2.894, P = 0.046 for TT genotype and OR = 0.346, P = 0.026 for non-TT genotype). In patients originating from Tabriz population, TT and non-TT genotypes and A allele revealed considerably different frequencies between the patient and control groups (OR = 3.043, P = 0.017; OR = 0.329, P = 0.013 and OR = 0.347, P = 0.048, respectively). Analysis of patients from Tehran also showed that there was a significant difference in the frequency of TT genotype between patients and controls (OR = 2.168, P = 0.04).

Conclusions

The results of the current study indicated a possible protective role for non-TT genotype in L9H variation CFB gene against AMD in a sample of the Iranian population. The region segregation results showed that TT genotype might be a risk factor for susceptibility to AMD.

Haplotypes of HTRA1 rs1120638, TIMP3 rs9621532, VEGFA rs833068, CFI rs10033900, ERCC6 rs3793784, and KCTD10 rs56209061 Gene Polymorphisms in Age-Related Macular Degeneration

BACKGROUND

To determine the impact of HTRA1 rs1120638, TIMP3 rs9621532, VEGFA rs833068, CFI rs10033900, ERCC6 rs3793784, and KCTD10 rs56209061 genotypes on the development of age-related macular degeneration (AMD) in the Lithuanian population.

METHODS

A total of 916 subjects were examined: 309 patients with early AMD, 301 patients with exudative AMD, and 306 healthy controls. The genotyping of HTRA1 rs11200638, TIMP3 rs9621532, VEGFA rs833068, CFI rs10033900, ERCC6 rs3793784, and KCTD10 rs56209061 was carried out using the RT-PCR method.

RESULTS

Our study showed that single-nucleotide polymorphisms rs3793784 and rs11200638 were associated with increased odds of early and exudative AMD, and the variant in KCTD10 (rs56209061) was found to be associated with decreased odds of early and exudative AMD development after adjustments for age and gender in early AMD analysis and after adjustments only for age in exudative AMD. The haplotype containing two minor alleles C-A and the G-A haplotype in rs3793784-rs11200638 were statistically significantly associated with an increased risk of exudative AMD development after adjustment for age, while the G-G haplotype showed a protective role against early and exudative AMD and the haplotype C-G in rs3793784-rs11200638 was associated with a decreased risk only of exudative AMD development.

CONCLUSIONS

Our study identified two markers, rs11200638 and rs3793784, as risk factors for early and exudative AMD, and one marker, rs56209061, as a protective factor for early and exudative AMD development. The haplotypes constructed of rs3793784-rs11200638 were found to be associated with AMD development, as well.

Complement factor B gene polymorphisms and risk of age-related macular degeneration: A meta-analysis

Objective:

To investigate the potential correlation between complement factor B polymorphisms and age-related macular degeneration.

Methods:

We retrieved relevant articles systematically by searching PubMed and Web of Science databases. The pooled odds ratios and 95% confidence intervals were calculated for five complement factor B polymorphism rs641153, rs4151667, rs1048709, rs2072633, and rs12614 using data from included articles in both random effects and fixed effect models. Subgroup meta-analysis based on age-related macular degeneration type, choroidal neovascular disease (rs641153 and rs4151667), geographic atrophy (rs641153 and rs4151667), and races was also performed.

Results:

In the overall comparison, we observed that the distribution of rs641153 and the risk of age-related macular degeneration were significantly correlated (p < 0.00001). Similar results were obtained in subgroup analysis based on race (Caucasians, p < 0.00001; Asians, p = 0.003) and age-related macular degeneration type (choroidal neovascular disease, p < 0.00001; geographic atrophy, p = 0.04). As for complement factor B rs4151667, the genotypic effects were also demonstrated statistically significant in overall analysis (p < 0.00001) and only in Caucasians diagnosed with choroidal neovascular disease (p = 0.004), but not in Asians. Moreover, no statistically significant correlations between the complement factor B polymorphisms rs1048709 (p = 0.63), rs2072633 (p = 0.72), rs12614 (p = 0.98) and susceptibility to age-related macular degeneration were detected in either overall or subgroup analysis.

Conclusion:

Collectively, we demonstrated that the complement factor B genes rs641153 and rs4151667, but not rs1048709, rs2072633, rs12614, were associated with the susceptibility of age-related macular degeneration and might play predictive roles in future age-related macular degeneration diagnosis. More studies are needed to verify these findings.

Association Between Complement Factor C2/C3/CFB/CFH Polymorphisms and Age-Related Macular Degeneration: A Meta-Analysis

BACKGROUND

Several previous studies have assessed the contribution of polymorphisms in genes encoding the complement factors C2/C3/CFB/CFH with the risk of age-related macular degeneration (AMD), however the results have been inconsistent. We conducted a meta-analysis to systematically review the potential association between complement factor polymorphisms and AMD.

METHODS

Studies that investigated associations between C2 (rs547154 and rs9332739), C3 (rs1047286), CFB (rs4151667 and rs641153), and CFH (rs551397 and rs2274700) polymorphisms and AMD were identified by searching PubMed, EMBASE, Web of Science, and Cochrane Library databases for articles published prior to January 1, 2018. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated to evaluate the association between these polymorphisms and AMD using Stata 12.0 software. Q and I² statistics were used to evaluate between-study heterogeneity. Publication bias analyses were conducted using Begg's test. We also conducted an ethnic subgroup analysis.

RESULTS

A total of 53 studies that included data for 53,774 patients and 56,973 healthy controls were evaluated. The pooled ORs for rs551397, rs2274700, rs4151667, rs641153, rs1047286, rs9332739, and rs547154 in the heterozygote model were 0.53 (95% CI: 0.45-0.61), 0.53 (95% CI: 0.40-0.70), 0.54 (95% CI: 0.46-0.63), 0.48 (95% CI: 0.4-0.57), 1.42 (95% CI: 1.22-1.66), 0.5 (95% CI: 0.45-0.56), and 0.52 (95% CI: 0.43-0.62), respectively.

CONCLUSION

Our findings from this analysis confirmed the protective role of C2/CFB/CFH polymorphisms in the development of AMD, but showed that the single nucleotide polymorphism in C3 was a high-risk factor for AMD. The racial analysis results suggested that the effect of variant alleles was stronger in Caucasians than Asians.

Sequence and Expression of Complement Factor H Gene Cluster Variants and Their Roles in Age-Related Macular Degeneration Risk

Purpose

To investigate how potentially functional genetic variants are coinherited on each of four common complement factor H (CFH) and CFH-related gene haplotypes and to measure expression of these genes in eye and liver tissues.

Methods

We sequenced the CFH region in four individuals (one homozygote for each of four common CFH region haplotypes) to identify all genetic variants. We studied associations between the haplotypes and AMD phenotypes in 2157 cases and 1150 controls. We examined RNA-seq profiles in macular and peripheral retina and retinal pigment epithelium/choroid/sclera (RCS) from eight eye donors and three liver samples.

Results

The haplotypic coinheritance of potentially functional variants (including missense variants, novel splice sites, and the CFHR3–CFHR1 deletion) was described for the four common haplotypes. Expression of the short and long CFH transcripts differed markedly between the retina and liver. We found no expression of any of the five CFH-related genes in the retina or RCS, in contrast to the liver, which is the main source of the circulating proteins.

Conclusions

We identified all genetic variants on common CFH region haplotypes and described their coinheritance. Understanding their functional effects will be key to developing and stratifying AMD therapies. The small scale of our expression study prevented us from investigating the relationships between CFH region haplotypes and their expression, and it will take time and collaboration to develop epidemiologic-scale studies. However, the striking difference between systemic and ocular expression of complement regulators shown in this study suggests important implications for the development of intraocular and systemic treatments.

A decade of age-related macular degeneration risk models: What have we learned from them and where are we going?

The genomic revolution has revealed the complexity of multifactorial diseases, making the development of effective diagnostics extremely challenging. In turn, the prospect of precision medicine as applied through targeted therapeutic treatments continues to remain largely elusive. Age-related macular degeneration (AMD) as a complex disease falls under this category, despite it being one of the most well characterized multifactorial diseases. This reflects both the extent of identified genetic components and known environmental risk factors. Additional considerations in dissecting out the roles played by genetic and non-genetic risk factors arise through the rapid increase in prevalence of AMD with age and the varying time periods over which disease progression can occur, complicating efforts to discriminate between "progressors" and non-"progressors." As a consequence, extensive research into the aetiology of AMD is yet to realize a clinically acceptable predictive test. This review covers the current climate of risk models in late AMD but will focus mainly on genetic risk factors as well as the types of models that have currently been employed in the AMD modelling literature.

Genetics of Unilateral and Bilateral Age-Related Macular Degeneration Severity Stages

Background

Age-related macular degeneration (AMD) is a common disease causing visual impairment and blindness. Various gene variants are strongly associated with late stage AMD, but little is known about the genetics of early forms of the disease. This study evaluated associations of genetic factors and different AMD stages depending on unilateral and bilateral disease severity.

Methods

In this case-control study, participants were assigned to nine AMD severity stages based on the characteristics of each eye. 18 single nucleotide polymorphisms (SNPs) were genotyped and attempted to correlate with AMD severity stages by uni- and multivariate logistic regression analyses and trend analyses. Area under the receiver operating characteristic curves (AUC) were calculated.

Results

Of 3444 individuals 1673 were controls, 379 had early AMD, 333 had intermediate AMD and 989 showed late AMD stages. With increasing severity of disease and bilateralism more SNPs with significant associations were found. Odds ratios, especially for the main risk polymorphisms in ARMS2 (rs10490924) and CFH (rs1061170), gained with increasing disease severity and bilateralism (exemplarily: rs1061170: unilateral early AMD: OR = 1.18; bilateral early AMD: OR = 1.20; unilateral intermediate AMD: OR = 1.28; bilateral intermediate AMD: OR = 1.39, unilateral geographic atrophy (GA): OR = 1.50; bilateral GA: OR = 1.71). Trend analyses showed p<0.0001 for ARMS2 (rs10490924) and for CFH (rs1061170), respectively. AUC of risk models for various AMD severity stages was lowest for unilateral early AMD (AUC = 0.629) and showed higher values in more severely and bilaterally affected individuals being highest for late AMD with GA in one eye and neovascular AMD in the other eye (AUC = 0.957).

Conclusion

The association of known genetic risk factors with AMD became stronger with increasing disease severity, which also led to an increasing discriminative ability of AMD cases and controls. Genetic predisposition was also associated with the disease severity of the fellow-eye, highlighting the importance of both eyes in AMD patients.

Changes of macular pigment optical density in elderly eyes: a longitudinal analysis from the MARS study

Background

Macular pigment (MP) has been related to the occurrence of age related macular degeneration (AMD). We investigated prospectively in eyes of elderly individuals how magnitude and spatial distribution of MP had changed after 4 years.

Methods

The study included 380 eyes from 237 participants of the Münster Ageing and Retina Study cohort which were free of advanced stages of AMD. MP optical density (MPOD) was measured in density units (D.U.) at eccentricities of 0.25°, 0.5°, 1.0° and 2.0° from the fovea using dual-wavelength autofluorescence; ring-like MP distributions were identified from MP density profiles. Changes were assessed with mixed linear models.

Results

The study participants’ mean age at baseline was 70.5 years. Early AMD was present in 150 study eyes (39.5 %) and a ring-like distribution of MPOD was found in 87 study eyes (22.9 %). After a median follow-up time of 3.96 years, the MPOD averaged over all eyes was slightly raised at the central fovea (from 0.658 to 0.670 D.U. (relative change +1.8 %), p = 0.08) and most markedly at 2.0° (from 0.157 to 0.172 D.U. (+9.5 %), p < 0.001). Multivariate analyses, adjusting for sex, body mass and carotenoid supplement intake, revealed that MPOD increments, at any distance from the fovea, were slightly less pronounced in older eyes. Serum concentrations of lutein at follow-up, presumably reflecting recent intake of antioxidant supplements, raised MPOD levels significantly at 1.0° and 2.0° (both p < 0.01) but not in the central fovea. Early AMD at baseline and ring-like MPOD distribution did not significantly impact on MPOD changes over time. A ring-like spatial distribution of MPOD persisted in over 80 % of the affected eyes.

Conclusions

Overall, the magnitude and spatial arrangement of MPOD was remarkably stable over time in elderly eyes. Significant MPOD rises in perifoveal regions probably indicate effects of lutein containing supplements. The persistence of ring-like MPOD distributions over time seems to suggest their determination by anatomical structures.

Electronic supplementary material

The online version of this article (doi:10.1186/s40942-016-0039-6) contains supplementary material, which is available to authorized users.

Fundus Autofluorescence and RPE Lipofuscin in Age-Related Macular Degeneration

Genes that increase susceptibility to age-related macular degeneration (AMD) have been identified; however, since many individuals carrying these risk alleles do not develop disease, other contributors are involved. One additional factor, long implicated in the pathogenesis of AMD, is the lipofuscin of retinal pigment epithelium (RPE). The fluorophores that constitute RPE lipofuscin also serve as a source of autofluorescence (AF) that can be imaged by confocal laser ophthalmoscopy. The AF originating from lipofuscin is excited by the delivery of short wavelength (SW) light. A second autofluorescence is emitted from the melanin of RPE (and choroid) upon near-infrared (NIR-AF) excitation. SW-AF imaging is currently used in the clinical management of retinal disorders and the advantages of NIR-AF are increasingly recognized. Here we visit the damaging properties of RPE lipofuscin that could be significant when expressed on a background of genetic susceptibility. To advance interpretations of disease-related patterns of fundus AF in AMD, we also consider the photochemical and spectrophotometric features of the lipofuscin compounds responsible for generating the fluorescence emission.

The role of the complement system in age-related macular degeneration

BACKGROUND

Age-related macular degeneration (AMD) is a common retinal disease in older people. In Europe, about 1.6% of persons over age 65 and more than 13% of persons over age 85 have late-stage AMD, which can severely impair vision. The development of AMD is influenced both by environmental factors and by a strong hereditary component.

METHOD

We selectively searched the PubMed database for articles published between April 2001 and November 2013 with the key words "age-related macular degeneration," "risk factor," "complement," and "therapy." The website www.clinicaltrials.gov was also used to search for relevant clinical trials.

RESULTS

Old age and smoking are confirmed risk factors for AMD. Moreover, genetic association studies have pointed to signaling pathways in which the complement system, a part of the individual's innate immune system, takes on a central role in the pathogenesis of the disease. Several clinical trials designed to interfere specifically with these pathomechanisms have yielded rather disappointing results, although a phase II study of the monoclonal antibody lampalizumab showed that blocking complement factor D lessened the progression of geographic atrophy. A risk model based on 13 genetic markers was found to have positive predictive values in predisposed individuals that ranged from 5.1% (in persons aged 65 to 69) to 91.7% (in persons aged 85 or older). It should be borne in mind that 50% of patients with AMD are not carriers of risk-associated markers.

CONCLUSION

There is no rationale at present for genetic testing to estimate the individual risk of developing AMD. Several recent clinical trials have incorporated current pathophysiological knowledge, but nearly all of these trials have yielded negative findings, with only one exception.

Identification of genome-wide SNP-SNP and SNP-clinical Boolean interactions in age-related macular degeneration

We propose here a methodology to uncover modularities in the network of SNP-SNP interactions most associated with disease. We start by computing all possible Boolean binary SNP interactions across the whole genome. By constructing a weighted graph of the most relevant interactions and via a combinatorial optimization approach, we find the most highly interconnected SNPs. We show that the method can be easily extended to find SNP/environment interactions. Using a modestly sized GWAS dataset of age-related macular degeneration (AMD), we identify a group of only 19 SNPs, which include those in previously reported regions associated to AMD. We also uncover a larger set of loci pointing to a matrix of key processes and functions that are affected. The proposed integrative methodology extends and overlaps traditional statistical analysis in a natural way. Combinatorial optimization techniques allow us to find the kernel of the most central interactions, complementing current methods of GWAS analysis and also enhancing the search for gene-environment interaction.

Relationship between the complement system, risk factors and prediction models in age-related macular degeneration

Studies performed over the past decade in humans and experimental animals have been a major source of information and improved our understanding of how dysregulation of the complement system contributes to age-related macular degeneration (AMD) pathology. Drusen, the hall-mark of dry-type AMD are reported to be the by-product of complement mediated inflammatory processes. In wet AMD, unregulated complement activation results in increased production of angiogenic growth factors leading to choroidal neovascularization both in humans and in animal models. In this review article we have linked the complement system with modifiable and non-modifiable AMD risk factors as well as with prediction models of AMD. Understanding the association between the complement system, risk factors and prediction models will help improve our understanding of AMD pathology and management of this disease.

The contribution of genetic factors to phenotype and progression of drusen in early age-related macular degeneration

PURPOSE

Genetic factors contribute to the development and progression of age-related macular degeneration (AMD). We aimed to assess the association of drusen as phenotypic characteristics of early AMD and their progression with polymorphisms in the CFH, ABCA1, and ARMS2 genes.

METHODS

In the Münster Aging and Retina Study (MARS), drusen were detected in 406 patients with early AMD and 170 healthy controls according to the International Classification using fundus photographs, with a follow-up examination after 2.6 years (median). Six drusen features were assessed: drusen number (</≥20); confluence of drusen (</≥50 %), largest drusen size (</≥175 μm); area occupied by drusen (</≥10 %); most frequent drusen size (</≥175 μm), and presence of soft, indistinct drusen (no/yes). Based on these features, an unweighted summary drusen severity score (DSS; categorized in "low", "intermediate" and "high") was calculated. The relationship of each drusen feature and the DSS with CFH rs1061170, ABCA1 rs1883025, and ARMS2 rs10490924 at baseline and after 2.6 years was analyzed using multivariate logistic regression models.

RESULTS

Cross-sectionally, each drusen feature was associated with a higher frequency of the CFH and ARMS2 risk variants. Compared to healthy eyes, the CFH risk variant was more common in eyes with early as well as advanced drusen features, while the ARMS2 variant was only associated with advanced drusen. After 2.6 years, 43 % of the eyes showed a progression of at least 1 unit in the DSS. The progression from low to higher DSS was inversely associated with ABCA1 (OR = 0.54), and the progression from intermediate to high DSS was positively related to CFH rs1061170 (OR = 2.3; p < 0.05 for each).

CONCLUSIONS

Variants in CFH, ABCA1, and ARMS2 genes are related to the presence and progression of drusen in early AMD. CFH and, inversely, ABCA1 seem to be involved in early drusen development, while the role of ARMS2 is more pronounced in advanced stages of early AMD.

Complement C3, C2, and factor B gene polymorphisms and age-related macular degeneration in a Greek cohort study

PURPOSE

To elucidate whether polymorphisms of C2, C3, and CFB genes are major genetic determinants of age-related macular degeneration (AMD) in a Greek population.

METHODS

This was a case-control association study comprising 120 Greek patients with early and late-stage AMD and 140 independent controls of Caucasian origin. All participants were genotyped for rs547154, rs2230199, rs641153, and rs12614 polymorphisms by a combination of PCR and direct DNA sequencing assays.

RESULTS

The frequency of the rs2230199 G allele (minor allele) was significantly higher in patients with AMD in comparison with controls (0.34 vs 0.22, p = 0.0031) and similar to the frequency of other reported populations. There was a significant difference in the frequencies of the rs2230199 genotypes among cases and controls (p = 0.0055). rs2230199 was found to be a significant predictor of advanced AMD status (odds ratio 6.41, confidence interval [CI] 2.72-15.09, p<0.0001; area under the curve 0.706, CI 0.61-0.78, p<0.0001]). For the other single nucleotide polymorphism (SNP) loci, the allele and genotype frequencies did not reach statistical significance. The minor allele frequencies in controls and cases were similar and still much lower than the frequencies reported in other populations.

CONCLUSIONS

The rs547154, rs641153, and rs12614 SNPs were not associated with AMD development in Greek patients. However, this finding should be viewed with caution as the particular polymorphisms presented with very low frequencies in the Greek population. Finally, the replication of the reported associations of C3 with AMD suggests that the presence of the C3 G allele could serve as a high-risk genetic marker for the development of AMD and the progression of the disease to the advanced clinical stage.

Age-Related Macular Degeneration: Pathogenesis, Genetic Background, and the Role of Nutritional Supplements

Age-related macular degeneration (ARMD) is the leading cause of severe vision loss and blindness worldwide, mainly affecting people over 65 years old. Dry and wet ARDM are the main types of the disease, which seem to have a multifactorial background. The aim of this review is to summarize the mechanisms of ARMD pathogenesis and exhibit the role of diet and nutritional supplements in the onset and progression of the disease. Environmental factors, such as smoking, alcohol, and, diet appear to interact with mutations in nuclear and mitochondrial DNA, contributing to the pathogenesis of ARMD. Inflammatory mediators and oxidative stress, induced by the daily exposure of retina to high pressure of oxygen and light radiation, have been also associated with ARMD lesions. Other than medical and surgical therapies, nutritional supplements hold a significant role in the prevention and treatment of ARMD, eliminating the progression of macular degeneration.

Complement factor B polymorphism (rs641153) and susceptibility to age-related macular degeneration: evidence from published studies

AIM

To determine whether single nucleotide polymorphism (SNP) rs641153 is associated with the risk of age-related macular degeneration (AMD), we performed a systematic meta-analysis of 15 eligible studies. SNP in the complement factor B (CFB) gene is considered to have significant association with AMD susceptibility, but there is great discrepancy in these results.

METHODS

The eligible studies were identified by searching the databases of PubMed, EMBASE, and Web of Science. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the association. All data were analyzed using Stata software.

RESULTS

The association between rs641153 and AMD risk was statistically significant under the homozygous model (AA vs GG:OR=0.26, 95%CI=0.15-0.45, P h=0.973, I (2)=0.0%, fixed effects), dominant model (AA+GA vs GG:OR=0.49, 95%CI=0.40-0.59, P h=0.004, I (2)=56.4%, random effects) and recessive model (AA vs GA+GG:OR=0.30, 95%CI=0.17-0.51, P h=0.983, I (2)=0.0%, fixed effects). The same results were also observed in the stratified analyses by ethnicity, source of control and sample size.

CONCLUSION

Our meta-analysis suggests that rs641153 in the CFB gene may play a protective role in AMD susceptibility, the late AMD in particular, both in Caucasians and in Asians.

Polymorphisms in ARMS2/HTRA1 and complement genes and age-related macular degeneration in India: findings from the INDEYE study

PURPOSE

Association between genetic variants in complement factor H (CFH), factor B (CFB), component 2 (C2), and in the ARMS2/HTRA1 region with age-related macular degeneration (AMD) comes mainly from studies of European ancestry and case-control studies of late-stage disease. We investigated associations of both early and late AMD with these variants in a population-based study of people aged 60 years and older in India.

METHODS

Fundus images were graded using the Wisconsin Age-Related Maculopathy Grading System and participants assigned to one of four mutually exclusive stages based on the worse affected eye (0 = no AMD, 1-3 = early AMD, 4 = late AMD). Multinomial logistic regression was used to derive risk ratios (RR) accounting for sampling method and adjusting for age, sex, and study center.

RESULTS

Of 3569 participants, 53.2% had no signs of amd, 45.6% had features of early amd, and 1.2% had late amd. CFH (RS1061170), C2 (RS547154), OR CFB (RS438999) was not associated with early or late AMD. In the ARMS2 locus, RS10490924 was associated with both early (adjusted RR 1.22, 95% confidence interval [CI]: 1.13-1.33, P < 0.0001) and late AMD (adjusted RR 1.81, 95% CI: 1.15-2.86; P = 0.01); rs2672598 was associated only with early AMD (adjusted RR 1.12, 95% CI: 1.02-1.23; P = 0.02); rs10490923 was not associated with early or late AMD.

CONCLUSIONS

Two variants in ARMS2/HTRA1 were associated with increased risk of early AMD, and for one of these, the increased risk was also evident for late AMD. The study provides new insights into the role of these variants in early stages of AMD in India.

The association between complement component 2/complement factor B polymorphisms and age-related macular degeneration: a HuGE review and meta-analysis

The authors performed a systematic review of the association of complement component 2(C2)/complement factor B (CFB) gene polymorphisms with age-related macular degeneration (AMD). In total, data from 19 studies published between 2006 and 2011 were pooled for 4 polymorphisms: rs9332739 and rs547154 in the C2 gene and rs4151667 and rs641153 in the CFB gene. Data extraction and assessments for risk of bias were independently performed by 2 reviewers. Allele frequencies and allele and genotypic effects were pooled. Heterogeneity and publication bias were explored. Pooled minor allele frequencies for all 4 SNPs were between 4.7% and 9.6% for all polymorphisms, except for an Indian population in which the C allele at rs9332739 was the major allele. For the C2 polymorphisms, the minor C allele at rs9332739 and the minor T allele at rs547154 carried estimated relative risks (odds ratios) of 0.55 (95% confidence interval (CI): 0.46, 0.65) and 0.47 (95% CI: 0.39, 0.57), respectively. For the CFB polymorphisms, the minor A alleles at rs4151667 and rs614153 carried estimated risks of 0.54 (95% CI: 0.45, 0.64) and 0.41 (95% CI: 0.34, 0.51), respectively. These allele effects contributed to an absolute lowering of the risk of all AMD in Caucasian populations by 2.0%-6.0%. This meta-analysis provides a robust estimate of the protective association of C2/CFB with AMD.

CFB/C2 gene polymorphisms and risk of age-related macular degeneration: a systematic review and meta-analysis

PURPOSE

To investigate whether the polymorphisms of CFB/C2 gene are associated with age-related macular degeneration (AMD), and to evaluate the magnitude of gene effect.

METHODS

We performed a meta-analysis of the association between four SNPs in CFB/C2 gene (rs9332739, rs547154, rs4151667, and rs641153) and risk of AMD using data from 15 case-control studies involving 8905 subjects. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using fixed- and random-effects models. The Q and I(2) statistics were used to evaluate between-study heterogeneity. Harbord's modified test was used to detect small study effects. Sensitivity analysis, cumulative meta-analysis, and meta-regression were also performed.

RESULTS

For rs9332739, rs547154, rs4151667, and rs641153, the pooled ORs in a dominant genetic model were 0.474 (fixed effects, P < 0.001, 95% CI 0.378-0.596), 0.399 (random effects, 95% CI 0.289-0.551, P < 0.001), 0.496 (fixed effects, 95% CI 0.390-0.632, P < 0.001), and 0.557 (random effects, P = 0.008, 95% CI 0.362-0.856), respectively. These results suggested that variant alleles of all the four SNPs has significant protective effect against AMD. Contour-enhanced funnel plots and Harbord's test showed moderate small study effects for rs9332739 and rs4151667. Heterogeneity were found for rs547154 and rs641153, subgroup analysis suggested that ethnicity was the main source for heterogeneity. Stratification by ethnicity indicated stronger protective effects of rare alleles in Caucasians. Genotype distribution analysis also suggested that frequencies of rare homozygous genotype were higher in Caucasian group.

CONCLUSIONS

Our meta-analysis indicated strong protective effects of the variant alleles of four SNPs in CFB/C2 gene (rs9332739, rs547154, rs4151667, and rs641153) against AMD. The disease risk descended to nearly one half for individuals carrying at least one copy of the rare alleles. The protective effects seemed to be stronger in Caucasians, of which the genotype frequencies were also higher.

Complement involvement in neovascular ocular diseases

Pathological neovascularization (NV) is a hallmark of late stage neovascular age-related macular degeneration (AMD), diabetic retinopathy (DR), and retinopathy of prematurity (ROP). There is accumulating evidence that alterations in inflammatory and immune system pathways that arise from genetic differences, injury, and disease can predispose individuals to retinal neovascular eye diseases. Yet the mechanism of disease progression with respect to the complement system in these maladies is not fully understood. Recent studies have implicated the complement system as an emerging player in the etiology of several retinal diseases. We will summarize herein several of the complement system pathways known to be involved in ocular neovascular pathologies. Current treatment for many neovascular eye diseases focuses on suppression of NV with laser ablation, photodynamic therapy, or anti-VEGF angiogenic inhibitors. However, these treatments do not address the underlying cause of many of these diseases. A clear understanding of the cellular and molecular mechanisms could bring a major shift in our approach to disease treatment and prevention.

Risk models for progression to advanced age-related macular degeneration using demographic, environmental, genetic, and ocular factors

PURPOSE

To expand our predictive models for progression to advanced stages of age-related macular degeneration (AMD) based on demographic, environmental, genetic, and ocular factors, using longer follow-up, time varying analyses, calculation of absolute risks, adjustment for competing risks, and detailed baseline AMD and drusen status.

DESIGN

Prospective, longitudinal study.

PARTICIPANTS

We included 2937 individuals in the Age-Related Eye Disease Study, of which 819 subjects progressed to advanced AMD during 12 years of follow-up.

METHODS

Cox proportional hazards regression analyses were performed to calculate hazard ratios for progression. Covariates included demographic and environmental factors, 6 variants in 5 genes, baseline macular drusen size, and presence and type of advanced AMD in 1 eye at baseline. To assess the ability of risk scores based on all covariates to discriminate between progressors and nonprogressors, an algorithm was developed and the area under the receiver operating characteristic curve (AUC) was calculated. To validate the overall model, the total sample was randomly subdivided into derivation and test samples. Another model was built based on the derivation sample and assessed for calibration and discrimination in the test sample. Sample sizes needed for testing new treatments in clinical trials were estimated based on models with and without genetic variables.

MAIN OUTCOME MEASURES

Progression to advanced AMD, including geographic atrophy and neovascular disease.

RESULTS

In multivariate models, age, smoking, body mass index, single nucleotide polymorphisms in the CFH, ARMS2/HTRA1, C3, C2, and CFB genes, as well as presence of advanced AMD in 1 eye and drusen size in both eyes were all independently associated with progression. The AUC for progression at 10 years in the model with genetic factors, drusen size, and environmental covariates was 0.915 in the total sample. In the test sample, based on a model estimated from the derivation sample, the AUC was 0.908. The sample sizes needed for clinical trials were estimated to be lower when genetic susceptibility was considered.

CONCLUSIONS

Factors reflective of nature and nurture were incorporated into an expanded algorithm for risk prediction, which performed very well in both derivation and test samples. Risk scores and predicted progression rates will be useful for AMD surveillance and for designing clinical trials.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found after the references.

Systematic review and meta-analysis of the association between complement component 3 and age-related macular degeneration: a HuGE review and meta-analysis

The authors performed a meta-analysis to estimate the magnitude of polymorphism effects for the complement component C3 gene (C3) and their possible mode of action on age-related macular degeneration (AMD). The meta-analysis included 16 and 7 studies for rs2230199 and rs1047286, respectively. Data extraction and risk of bias assessments were performed in duplicate, and heterogeneity and publication bias were explored. There was moderate evidence for association between both polymorphisms and AMD in Caucasians. For rs2230199, patients with CG and GG genotypes were 1.44 (95% confidence interval (CI): 1.33, 1.56) and 1.88 (95% CI: 1.59, 2.23) times more likely to have AMD than patients with the CC genotype. For rs1047286, GA and AA genotypes had 1.27 (95% CI: 1.15, 1.41) and 1.70 (95% CI: 1.27, 2.11) times higher risk of AMD than did GG genotypes. These gene effects suggested an additive model. The population attributable risks for the GG/GC and AA/GA genotypes are approximately 5%-10%. Subgroup analysis by ethnicity indicates that these variants are very infrequent in Asians and that the observed gene effects are based largely on the high frequency within Caucasian populations. This meta-analysis supports the association between C3 and AMD and provides a robust estimate of the genetic risk.

Genetics of age-related macular degeneration: current concepts, future directions

Age-related macular degeneration (AMD) is a progressive degenerative disease which leads to blindness, affecting the quality of life of millions of Americans. More than 1.75 million individuals in the United States are affected by the advanced form of AMD. The etiological pathway of AMD is not yet fully understood, but there is a clear genetic influence on disease risk. To date, the 1q32 (CFH) and 10q26 (PLEKHA1/ARMS2/HTRA1) loci are the most strongly associated with disease; however, the variation in these genomic regions alone is unable to predict disease development with high accuracy. Therefore, current genetic studies are aimed at identifying new genes associated with AMD and their modifiers, with the goal of discovering diagnostic or prognostic biomarkers. Moreover, these studies provide the foundation for further investigation into the pathophysiology of AMD by utilizing a systems-biology-based approach to elucidate underlying mechanistic pathways.