The LOC387715 Gene, Smoking, Body Mass Index, Environmental Associations with Advanced Age-Related Macular Degeneration

Exploring the contribution of ARMS2 and HTRA1 genetic risk factors in age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of severe irreversible central vision loss in individuals over 65 years old. Genome-wide association studies (GWASs) have shown that the region at chromosome 10q26, where the age-related maculopathy susceptibility (ARMS2/LOC387715) and HtrA serine peptidase 1 (HTRA1) genes are located, represents one of the strongest associated loci for AMD. However, the underlying biological mechanism of this genetic association has remained elusive. In this article, we extensively review the literature by us and others regarding the ARMS2/HTRA1 risk alleles and their functional significance. We also review the literature regarding the presumed function of the ARMS2 protein and the molecular processes of the HTRA1 protein in AMD pathogenesis in vitro and in vivo, including those of transgenic mice overexpressing HtrA1/HTRA1 which developed Bruch's membrane (BM) damage, choroidal neovascularization (CNV), and polypoidal choroidal vasculopathy (PCV), similar to human AMD patients. The elucidation of the molecular mechanisms of the ARMS2 and HTRA1 susceptibility loci has begun to untangle the complex biological pathways underlying AMD pathophysiology, pointing to new testable paradigms for treatment.

10q26 - The enigma in age-related macular degeneration

Despite comprehensive research efforts over the last decades, the pathomechanisms of age-related macular degeneration (AMD) remain far from being understood. Large-scale genome wide association studies (GWAS) were able to provide a defined set of genetic aberrations which contribute to disease risk, with the strongest contributors mapping to distinct regions on chromosome 1 and 10. While the chromosome 1 locus comprises factors of the complement system with well-known functions, the role of the 10q26-locus in AMD-pathophysiology remains enigmatic. 10q26 harbors a cluster of three functional genes, namely PLEKHA1, ARMS2 and HTRA1, with most of the AMD-associated genetic variants mapping to the latter two genes. High linkage disequilibrium between ARMS2 and HTRA1 has kept association studies from reliably defining the risk-causing gene for long and only very recently the genetic risk region has been narrowed to ARMS2, suggesting that this is the true AMD gene at this locus. However, genetic associations alone do not suffice to prove causality and one or more of the 14 SNPs on this haplotype may be involved in long-range control of gene expression, leaving HTRA1 and PLEKHA1 still suspects in the pathogenic pathway. Both, ARMS2 and HTRA1 have been linked to extracellular matrix homeostasis, yet their exact molecular function as well as their role in AMD pathogenesis remains to be uncovered. The transcriptional regulation of the 10q26 locus adds an additional level of complexity, given, that gene-regulatory as well as epigenetic alterations may influence expression levels from 10q26 in diseased individuals. Here, we provide a comprehensive overview on the 10q26 locus and its three gene products on various levels of biological complexity and discuss current and future research strategies to shed light on one of the remaining enigmatic spots in the AMD landscape.

Posterior Vitreous Detachment and Its Role in the Evolution of Dry to Wet Age Related Macular Degeneration

Purpose

To examine the state of the posterior vitreous in eyes with exudative age-related macular degeneration, AMD, non-exudative AMD and in normal eyes.

Study

This is a prospective, cross-sectional study.

Methods

B-scan ultrasonography and Optical Coherence Tomography, OCT were performed in 165 patients older than 65 years with any AMD and in 22 patients older than 65 years with normal eyes in order to diagnose the eyes with complete posterior vitreous detachment, PVD and the eyes with persistent central vitreomacular adhesion, VMA. All patients were selected from the outpatient clinic of the Ophthalmology Department in the University Hospital of Patras. Fundus Fluoroangiography, FFA was used in order to determine the development of exudative AMD from non-exudative AMD. Follow up time was 48 months.

Results

16/171 eyes with exudative AMD (9.36%) had complete PVD, and the rest 155/171 (90.64%) had central VMA. Eleven of 138 eyes with non-exudative AMD (7.97%) had complete PVD and the remaining 127 eyes (92.03%) had central VMA. During the 48 months of the study, 28 eyes, all with central VMA progressed to exudative AMD.

Conclusion

Vitreomacular adhesion is associated with both exudative and non-exudative AMD. Progression of the non-exudative eyes to exudative AMD seems to be lower in eyes with complete PVD. On the other hand, the progression of normal eyes to exudative AMD appears to be independent of the posterior vitreous status. Larger and longer studies need to replicate these findings and support the potential of a protective role of complete posterior vitreous detachment in the evolution of the disease.

Comparison of machine learning tools for the prediction of AMD based on genetic, age, and diabetes-related variables in the Chinese population

Introduction

Age-related macular degeneration (AMD) is the main cause of visual impairment and the most important cause of blindness in older people. However, there is currently no effective treatment for this disease, so it is necessary to establish a risk model to predict AMD development.

Methods

This study included a total of 202 subjects, comprising 82 AMD patients and 120 control subjects. Sixty-six single-nucleotide polymorphisms (SNPs) were identified using the MassArray assay. Considering 14 independent clinical variables as well as SNPs, four predictive models were established in the training set and evaluated by the confusion matrix, area under the receiver operating characteristic (ROC) curve (AUROC). The difference distributions of the 14 independent clinical features between the AMD and control groups were tested using the chi-squared test. Age and diabetes were adjusted using logistic regression analysis and the “genomic-control” method was used for multiple testing correction.

Results

Three SNPs (rs10490924, OR = 1.686, genomic-control corrected p-value (GC) = 0.030; rs2338104, OR = 1.794, GC = 0.025 and rs1864163, OR = 2.125, GC = 0.038) were significant risk factors for AMD development. In the training set, four models obtained AUROC values above 0.72.

Conclusions

We believe machine learning tools will be useful for the early prediction of AMD and for the development of relevant intervention strategies.

Macular retinal thickness differs markedly in age-related macular degeneration driven by risk polymorphisms on chromosomes 1 and 10

The two most common genetic contributors to age-related macular degeneration (AMD), a leading cause of irreversible vision loss worldwide, are variants associated with CFH-CFHR5 on chromosome 1 (Chr1) and ARMS2/HTRA1 on chromosome 10 (Chr10). We sought to determine if risk and protective variants associated with these two loci drive differences in macular retinal thickness prior and subsequent to the onset of clinically observable signs of AMD. We considered 299 individuals (547 eyes) homozygous for risk variants or haplotypes on Chr1 or Chr10 exclusively (Chr1-risk and Chr10-risk, respectively) or homozygous for a neutral haplotype (Chr1-neu), for the protective I62 tagged haplotype (Chr1-prot-I62) or for the protection conferring CFHR1/3 deletion haplotype (Chr1-prot-del) on Chr1 without any risk alleles on Chr10. Among eyes with no clinically observable signs of AMD, the deletion of CFHR1/3, which is strongly protective against this disease, is associated with significantly thicker retinas in the perifovea. When controlling for age, Chr10-risk eyes with early or intermediate AMD have thinner retinas as compared to eyes from the Chr1-risk group with similar disease severity. Our analysis indicates that this difference likely results from distinct biological and disease initiation and progression events associated with Chr1- and Chr10-directed AMD.

Quantitative Assessment of Choriocapillaris Flow Deficits in Eyes with Advanced Age-Related Macular Degeneration Versus Healthy Eyes

PURPOSE

To compare choriocapillaris (CC) flow deficits in eyes with geographic atrophy (GA) or choroidal neovascularization (CNV) associated with age-related macular degeneration (AMD) and age-matched healthy control subjects.

DESIGN

Cross-sectional study.

METHODS

Patients with GA due to AMD, CNV due to AMD, and age-matched healthy subjects presenting to the Doheny-UCLA Eye Centers were enrolled in this cross-sectional institutional review board-approved study. Swept-source optical coherence tomography angiography was performed using a Zeiss PLEX Elite instrument with a 6 × 6-mm scan pattern centered on the fovea. Two repeated volume scans were acquired to allow for image averaging. The instrument predefined en face slab of the CC was used to isolate and display the CC. Both the structural and optical coherence tomography angiography slabs from this location were exported for averaging and signal compensation using Image J. The resultant image was then binarized. The CC flow deficit percentage (FD%) was computed in 4 peripheral 1 × 1-mm squares located at the corners of the images to allow comparison between equidistant regions unaffected by atrophy or CNV.

RESULTS

Twenty eyes of 20 subjects were enrolled in each of the 3 groups (CNV, GA, normal) for this study. The average CC FD% of the 4 peripheral squares was 17.24% ± 2.86% in GA eyes, 15.55% ± 1.03% in CNV eyes, and 15.31% ± 0.93% in healthy controls of a similar age. The FD% in GA eyes was significantly greater than in both normal eyes and eyes with CNV (p= 0.012 and 0.038 respectively). The difference in FD% was not significantly different between CNV eyes and normal eyes for the tested peripheral macular regions (P = .678).

CONCLUSIONS

The CC in peripheral macular regions in eyes with GA shows greater impairment than in eyes with CNV.

Fellow Eye Status Is a Biomarker for the Progression Rate of Geographic Atrophy: A Systematic Review and Meta-analysis

TOPIC

Systematic review and meta-analysis of how fellow eye status predicts the progression rate of geographic atrophy (GA).

CLINICAL RELEVANCE

The status of age-related macular degeneration (AMD) in the fellow eye has been used as an indicator of the GA progression rates in primary eyes, but the reported growth rates vary widely in prior clinical studies.

METHODS

We searched MEDLINE, EMBASE, Cochrane Library, Clinicaltrials.gov, and PubMed up to September 12, 2018, for studies that classified treatment-naive GA patients based on different AMD manifestations in the fellow eyes and that monitored GA progression in the primary eyes. Three fellow eye statuses were analyzed: (1) no GA or choroidal neovascularization (CNV) in the fellow eye, (2) GA in the fellow eye, and (3) CNV in the fellow eye. To account for the patients' different entry times, we introduced a horizontal translation factor to shift each dataset within each group. We determined the translation factor by adjusting it 1 month at a time until the r² in weighted least squares regression (r²_WLS) was maximized for the cumulative linear trend line of all datasets. Heterogeneity and study quality were assessed using the I² statistic and Newcastle-Ottawa scale, respectively. Publication bias was evaluated by funnel plots, the Egger test, and the Begg test.

RESULTS

We included 9 studies with 2134 eyes from 1835 patients. After the introduction of translation factors, the datasets in each fellow eye group fit along a straight line with a high r²_WLS. The GA radius growth rate in fellow eyes with GA (0.179±0.003 mm/year) and fellow eyes with CNV (0.159±0.015 mm/year) was significantly higher than that in fellow eyes without GA or CNV (0.110±0.009 mm/year; P < 0.001 and P = 0.02, respectively). We found no significant difference in the GA radius growth rates between fellow eyes with GA and fellow eyes with CNV (P = 0.42).

CONCLUSIONS

We confirmed that the presence of advanced AMD in the fellow eye, defined as GA or CNV, can serve as a biomarker of the GA enlargement rate in the primary eye. This may assist the design of clinical trials and may shed light on the natural history of GA expansion.

The vitreomacular interface in different types of age-related macular degeneration

AIM

To evaluate the vitreomacular interface in cases with wet age-related macular degeneration (AMD) and to compare them to eyes with dry AMD and normal eyes.

METHODS

This was a cross-sectional comparative study that included 87 eyes with wet AMD, 42 eyes with dry AMD and 40 eyes without AMD as a control group. Optical coherence tomography (OCT) examination was performed for all patients to assess the vitreomacular interface.

RESULTS

In the wet AMD group, 34.5% of cases had vitreomacular adhesion (VMA). Only 14.3% of dry AMD cases and 10% of control cases had VMA. There was a significant difference between the control group and the wet AMD group (P=0.004) as well as the dry and wet AMD group (P=0.017). There was also a significant difference between the incidence of VMA in patients with subretinal choroidal neovascularization (CNV, type 1) and intraretinal CNV (type 2 or type 3) (P=0.020).

CONCLUSION

There is an association between posterior vitreous attachment and AMD. There is also an increased incidence of VMA with intra-retinal CNV.

Geographic Atrophy and Choroidal Neovascularization in the Same Eye: A Review

Geographic atrophy (GA) and choroidal neovascularization (CNV), the two late forms of age-related macular degeneration, are generally considered two distinct entities. However, GA and CNV can occur simultaneously in the same eye, with GA usually occurring first. The prevalence of this combined entity is higher in histological studies than in clinical studies. No distinct systemic or genetic risk characteristics are associated with the combined GA/CNV entity, although on clinical examination and retinal imaging it can feature drusen or subretinal drusenoid deposits. GA and CNV may exist within the spectrum of a single disease, or they may be two very different diseases. Therapy with antivascular endothelial growth factor (anti-VEGF) is often successful for CNV, but some evidence suggests increased rates of GA development in eyes treated with anti-VEGF. In this article, we review the current literature regarding the epidemiology, clinical presentation, and treatment options for patients with the combined GA/CNV entity.

Association between SERPING1 rs2511989 polymorphism and age-related macular degeneration: Meta-analysis

AIM

To investigate the association between SERPING1 rs2511989 (G>A) polymorphism and age-related macular degeneration (AMD).

METHODS

A number of electronic databases (up to July 15, 2014) were searched independently by two investigators. A Meta-analysis was performed on the association between SERPING1 rs2511989 polymorphism and AMD. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were estimated.

RESULTS

Eight studies with 16 cohorts consisting of 9163 cases and 6813 controls were included in this Meta-analysis. There was no significant association between rs2511989 polymorphism and AMD under all genetic models in overall estimates (A vs G: OR= 0.938, 95%CI =0.858-1.025; AA vs GG:OR =0.871, 95%CI =0.719-1.056; AG vs GG: OR =0.944, 95%CI =0.845-1.054; AA+AG vs GG: OR =0.927, 95% CI =0.823-1.044; AA vs AG+GG: OR =0.890, 95%CI =0.780-1.034). Cumulative Meta-analyses also showed a trend of no association between rs2511989 polymorphism and AMD as information accumulated by year. Subgroup analysis and Meta-regression analysis indicated that age-matching status was the main source of heterogeneity. Sensitivity analysis found the results in overall comparisons and subgroup comparisons of white subjects under the allele model were found to have significantly statistical differences after studies deviating from Hardy-Weinberg equilibrium (HWE) were excluded (overall: OR=0.918, 95%CI = 0.844-0.999, P =0.049; whites: OR =0.901, 95%CI = 0.817-0.994, P =0.038). However, the results were not sufficiently robust for further sensitivity analysis and statistical differences disappeared on applying Bonferroni correction (with a significance level set at 0.05/25).

CONCLUSION

This Meta-analysis indicates that SERPING1 rs2511989 polymorphism and AMD tend to have no association with each other. Age matching status is a big confounding factor, and more studies with subtle designs are warranted in future.

Risk characteristics of the combined geographic atrophy and choroidal neovascularisation phenotype in age-related macular degeneration

AIM

To investigate the risk characteristics of the combined geographic atrophy (GA) and choroidal neovascularisation (CNV) phenotype of age-related macular degeneration (AMD) compared to GA or CNV.

METHODS

Patients with advanced AMD were identified and divided into three groups using multimodal imaging: patients with GA in at least one eye, patients with CNV in at least one eye, and patients with simultaneous GA and CNV in at least one eye. Epidemiologic and clinical factors were gathered from patient questionnaires. Genotypes for age-related maculopathy susceptibility 2 (ARMS2) and complement factor H (CFH) were determined.

RESULTS

42 patients with GA or CNV, and 16 patients with combined GA/CNV were identified. Patients with the combined phenotype were older (86.4 vs 81.8 years, p=0.049), and had a higher prevalence of advanced AMD in the fellow eye (81.3% vs 31.0%, p<0.001). CFH and ARMS2 risk alleles were not associated with the combined phenotype.

CONCLUSIONS

The combined GA/CNV phenotype has similar epidemiologic, clinical, and genetic features as GA and CNV, but occurs at an older age and is more associated with advanced AMD in the fellow eye, suggesting that all these phenotypes are part of the same spectrum of disease and that the combined phenotype represents an even more advanced form of AMD than either GA or CNV.

Nature and nurture- genes and environment- predict onset and progression of macular degeneration

Age-related macular degeneration (AMD) is a common cause of irreversible visual loss and the disease burden is rising world-wide as the population ages. Both environmental and genetic factors contribute to the development of this disease. Among environmental factors, smoking, obesity and dietary factors including antioxidants and dietary fat intake influence onset and progression of AMD. There are also several lines of evidence that link cardiovascular, immune and inflammatory biomarkers to AMD. The genetic etiology of AMD has been and continues to be an intense and fruitful area of investigation. Genome-wide association studies have revealed numerous common variants associated with AMD and sequencing is increasing our knowledge of how rare genetic variants strongly impact disease. Evidence for interactions between environmental, therapeutic and genetic factors is emerging and elucidating the mechanisms of this interplay remains a major challenge in the field. Genotype-phenotype associations are evolving. The knowledge of non-genetic, modifiable risk factors along with information about heritability and genetic risk variants for this disease acquired over the past 25 years have greatly improved patient management and our ability to predict which patients will develop or progress to advanced forms of AMD. Personalized medicine and individualized prevention and treatment strategies may become a reality in the near future.

Chromosome 10q26 locus and age-related macular degeneration: a progress update

Age-related macular degeneration (AMD) is the leading cause of late-onset central vision loss in developed countries. Both genetic and environmental factors contribute to the onset of AMD. Variation at a locus on chromosome 10q26 has been consistently associated with this disease and represents one of the two strongest genetic effects being identified in AMD. At least three genes are located within the bounds of the locus: pleckstrin homology domain containing family A member 1 (PLEKHA1), age-related maculopathy susceptibility 2 (ARMS2) and high-temperature requirement A serine peptidase 1 (HTRA1), all of which are associated with AMD. Due to the strong linkage disequilibrium (LD) across this region, statistical genetic analysis alone is incapable of distinguishing the effect of an individual gene in the locus. Uncertainty remains, however, in regards to which gene is responsible for the linkage and association of the locus with AMD. Investigating functional consequences of the associated variants and related genes tends to be essential to identifying the biologically responsible gene(s) underlying AMD. This review examines the recent progress and current uncertainty on the genetic and functional analyses of the 10q26 locus in AMD with a focus on ARMS2 and HTRA1. A discussion, which entails the possible multi-faceted approaches for pinpointing the gene(s) in the locus underlying the pathogenesis of AMD, is also included.

Predictive model for earlier diagnosis of suspected age-related macular degeneration patients

The primary goal of tailored medicine is to presymptomatically identify individuals at high risk for disease using information of each individual's genetic profile and collection of environmental risk factors. Recently, algorithms were given the strong recognition of several replicated risk factors for age-related macular degeneration (AMD), this distant goal is beginning to seem less mysterious. The purpose of the study was to develop a statistical model for AMD. This study includes total 106 subjects. To identify the risk of earlier diagnosis of suspected AMD patients, 22 independent variables were included in the study. Forward stepwise (likelihood ratio) binary logistic regression has been used to find significant variables associated with the risk of AMD. Prediction equation, based on significant risk factors, and model authenticity have been developed. Hosmer-Lemeshow goodness of fit statistic (χ(2)=0.143, df=8, p=1.0), which is nonsignificant, indicates the appropriateness of the logistic regression model to predict AMD. After going through stepwise logistic regression, only 6 variables out of the 22 independent variables, namely, serum complement factor H (CFH), serum chemokine (C-C motif) ligand 2 (CCL2), serum superoxide dismutase 1 (SOD1), polymorphism in CCL2 (rs4586), stress, and comorbidity were found to be significant (p<0.05). The binary logistic regression model is an appropriate tool to predict AMD in the presence of serum CFH, serum CCL2, serum SOD1, polymorphism in CCL2 (rs4586), stress, and comorbidity with high specificity and sensitivity. The area under the receiver operating characteristic curve (0.909, p=0.001) with less standard error of 0.034 and close 95% confidence intervals (0.842-0.976) further validates the model.

Association between vascular endothelial growth factor +936 C/T gene polymorphism and age-related macular degeneration

Objectives

The pathogenesis of age-related macular degeneration (AMD) remains unknown. Vascular endothelial growth factor (VEGF) is an important regulator of angiogenesis and a target for inhibition therapy in wet AMD. This study investigated the association between the VEGF +936 C/T gene polymorphism and AMD, in a Chinese Han population.

Methods

Patients with AMD, and age- and sex-matched controls were enrolled. Restriction fragment length polymorphism was used to analyse the VEGF +936 polymorphism in the promoter and the 3′ untranslated region of the gene.

Results

The study included 200 AMD patients and 200 control subjects. There was a significantly higher prevalence of the TT genotype among AMD patients (9.0%) compared with controls (3.5%); the odds ratio for this genotype in AMD patients was 2.73 (95% confidence intervals 1.11, 6.68). There were no significant associations between any genotype and AMD subphenotypic categories (early, geographic atrophy, choroidal neovascularization).

Conclusions

The present study findings suggested that the VEGF +936 TT genotype was associated with AMD among Han Chinese patients.

Mitochondrial DNA haplogroups confer differences in risk for age-related macular degeneration: a case control study

BACKGROUND

Age-related macular degeneration (AMD) is the leading cause of vision loss in elderly, Caucasian populations. There is strong evidence that mitochondrial dysfunction and oxidative stress play a role in the cell death found in AMD retinas. The purpose of this study was to examine the association of the Caucasian mitochondrial JTU haplogroup cluster with AMD. We also assessed for gender bias and additive risk with known high risk nuclear gene SNPs, ARMS2/LOC387715 (G > T; Ala69Ser, rs10490924) and CFH (T > C; Try402His, rs1061170).

METHODS

Total DNA was isolated from 162 AMD subjects and 164 age-matched control subjects located in Los Angeles, California, USA. Polymerase chain reaction (PCR) and restriction enzyme digestion were used to identify the J, U, T, and H mitochondrial haplogroups and the ARMS2-rs10490924 and CFH-rs1061170 SNPs. PCR amplified products were sequenced to verify the nucleotide substitutions for the haplogroups and ARMS2 gene.

RESULTS

The JTU haplogroup cluster occurred in 34% (55/162) of AMD subjects versus 15% (24/164) of normal (OR = 2.99; p = 0.0001). This association was slightly greater in males (OR = 3.98, p = 0.005) than the female population (OR = 3.02, p = 0.001). Assuming a dominant effect, the risk alleles for the ARMS2 (rs10490924; p = 0.00001) and CFH (rs1061170; p = 0.027) SNPs were significantly associated with total AMD populations. We found there was no additive risk for the ARMS2 (rs10490924) or CFH (rs1061170) SNPs on the JTU haplogroup background.

CONCLUSIONS

There is a strong association of the JTU haplogroup cluster with AMD. In our Southern California population, the ARMS2 (rs10490924) and CFH (rs1061170) genes were significantly but independently associated with AMD. SNPs defining the JTU mitochondrial haplogroup cluster may change the retinal bioenergetics and play a significant role in the pathogenesis of AMD.

Effects of smoking on ocular health

PURPOSE OF REVIEW

To review recent data on the effects of smoking on ocular health.

RECENT FINDINGS

Smoking has been associated with a myriad of negative ocular health effects including age-related macular degeneration (ARMD) and cataract. Most recently, several papers have demonstrated a connection between smoking and ocular inflammation. Smokers are both more likely to develop ocular inflammation and to have more severe disease as manifested by poorer presenting vision and a higher risk of recurrent disease compared to nonsmokers. Smoking has also been shown to enhance the effect of genetic susceptibility with regards to the presence and development of ARMD. Finally, the negative effects of smoking on ocular disease have been increasingly documented in nonwhite populations outside of the USA. However, despite the abundance of data, public awareness on the adverse consequences of smoking on vision is lacking in the USA. In contrast, Australia improved public knowledge by launching a successful antitobacco health campaign highlighting the effects of smoking on ocular health.

SUMMARY

These findings suggest that eye care professionals should discuss and offer options for smoking cessation as part of the management of patients with ocular diseases, especially in those with ocular inflammation, ARMD, lens opacities/cataract, and thyroid-associated orbitopathy. Health campaigns using existing medical data can improve public awareness on the connection between tobacco and visual impairment.

Update on the role of genetics in the onset of age-related macular degeneration

Age-related macular degeneration (AMD), akin to other common age-related diseases, has a complex pathogenesis and arises from the interplay of genes, environmental factors, and personal characteristics. The past decade has seen very significant strides towards identification of those precise genetic variants associated with disease. That genes encoding proteins of the (alternative) complement pathway (CFH, C2, CFB, C3, CFI) are major players in etiology came as a surprise to many but has already lead to the development of therapies entering human clinical trials. Other genes replicated in many populations ARMS2, APOE, variants near TIMP3, and genes involved in lipid metabolism have also been implicated in disease pathogenesis. The genes discovered to date can be estimated to account for approximately 50% of the genetic variance of AMD and have been discovered by candidate gene approaches, pathway analysis, and latterly genome-wide association studies. Next generation sequencing modalities and meta-analysis techniques are being employed with the aim of identifying the remaining rarer but, perhaps, individually more significant sequence variations, linked to disease status. Complementary studies have also begun to utilize this genetic information to develop clinically useful algorithms to predict AMD risk and evaluate pharmacogenetics. In this article, contemporary commentary is provided on rapidly progressing efforts to elucidate the genetic pathogenesis of AMD as the field stands at the end of the first decade of the 21st century.

Genetic factors associated with age-related macular degeneration

Age-related macular degeneration (AMD) is a complex, multifactorial disease associated with environmental and genetic factors. This review emphasizes the clinical impact of the major genetic factors mainly located in the complement factor H gene and on the 10q26 locus, and their current and future implications for the management of AMD.

Smoking, dietary betaine, methionine, and vitamin D in monozygotic twins with discordant macular degeneration: epigenetic implications

OBJECTIVE

We evaluated monozygotic twin pairs with discordant age-related macular degeneration (AMD) phenotypes to assess differences in behavioral and nutritional factors.

DESIGN

Case series.

PARTICIPANTS

Caucasian male twin pairs from the United States Twin Study of Macular Degeneration.

METHODS

Twin pairs were genotyped to confirm monozygosity. Ocular characteristics were evaluated based on fundus photographs using the Wisconsin Grading System and a 5-grade Clinical Age-Related Maculopathy Staging System. We selected twin pairs discordant in each of the following phenotypic categories: Stage of AMD (n = 28), drusen area (n = 60), drusen size (n = 40), and increased pigment area (n = 56). The Wilcoxon signed-rank test and linear regression were used to assess associations between behavioral and nutritional characteristics and each phenotype within discordant twin pairs.

MAIN OUTCOME MEASURES

Differences in smoking and dietary factors within twin pairs discordant for stage of AMD, drusen area, drusen size, and pigment area.

RESULTS

Representative fundus photographs depict the discordant phenotypes. Pack-years of smoking were higher for the twin with the more advanced stage of AMD (P = 0.05). Higher dietary intake of vitamin D was present in the twins with less severe AMD (P = 0.01) and smaller drusen size (P = 0.05) compared with co-twins, adjusted for smoking and age. Dietary intakes of betaine and methionine were significantly higher in the twin with lower stage of AMD (P = 0.009) and smaller drusen area (P = 0.03), respectively.

CONCLUSIONS

The twin with the more advanced stage of AMD, larger drusen area, drusen size, and pigment area tended to be the heavier smoker. The twin with the earlier stage of AMD, smaller drusen size and area, and less pigment tended to have higher dietary vitamin D, betaine, or methionine intake. Results suggest that behavioral and nutritional factors associated with epigenetic mechanisms are involved in the etiology of AMD, in addition to genetic susceptibility.

Polymorphisms in ARMS2 (LOC387715) and LOXL1 genes in the Japanese with age-related macular degeneration

PURPOSE

To determine whether polymorphisms in the ARMS2 (LOC387715) gene and the lysyl oxidase-like 1 (LOXL1) gene are associated with age-related macular degeneration (AMD) in Japanese patients.

DESIGN

Clinically relevant laboratory investigation.

METHODS

Forty-one unrelated Japanese subjects with dry AMD, 50 subjects with exudative (wet) AMD, and 60 subjects with polypoidal choroidal vasculopathy (PCV) were studied. The single nucleotide polymorphisms (SNPs), p.Ala69Ser of the ARMS2 gene and p.Arg141Leu of the LOXL1 gene, were amplified by polymerase chain reaction, directly sequenced, and genotyped.

RESULTS

For the ARMS2 gene, the genotype frequency of the p.Ala69Ser single nucleotide polymorphism in eyes with dry AMD was not significantly different from that in the controls (P = .04), but the frequency was significantly higher in the exudative AMD group (P = 3.1 × 10(-8)) and PCV group (P = 6.9 × 10(-3)). For the LOXL1 gene, the genotype frequency of the p.Arg141Leu single nucleotide polymorphism was not statistically higher in the dry AMD and PCV groups than in the control group (dry AMD, P = .05; PCV, P = .16), but was statistically higher in the exudative AMD group (P = 6.8 × 10(-3)). Regression analyses showed significant associations between the ARMS2 gene and LOXL1 gene in patients with exudative AMD.

CONCLUSIONS

The p.Ala69Ser polymorphism of the ARMS2 gene is strongly associated with exudative AMD and PCV and is associated marginally with dry AMD. The polymorphisms in the LOXL1 gene did not predispose the individual to dry AMD and PCV. These findings suggest that there is a significant association between the ARMS2 gene and LOXL1 gene in exudative AMD.

Association study of complement factor H, C2, CFB, and C3 and age-related macular degeneration in a Han Chinese population

PURPOSE

Genes in the complement pathway, including complement factor H (CFH), C2/BF, and C3, have been reported to be associated with age-related macular degeneration (AMD). Genetic variants, single-nucleotide polymorphisms (SNPs), in these genes were geno-typed for a case-control association study in a mainland Han Chinese population.

METHODS

One hundred and fifty-eight patients with wet AMD, 80 patients with soft drusen, and 220 matched control subjects were recruited among Han Chinese in mainland China. Seven SNPs in CFH and two SNPs in C2, CFB', and C3 were genotyped using the ABI SNaPshot method. A deletion of 84,682 base pairs covering the CFHR1 and CFHR3 genes was detected by direct polymerase chain reaction and gel electrophoresis.

RESULTS

Four SNPs, including rs3753394 (P = 0.0276), rs800292 (P = 0.0266), rs1061170 (P = 0.00514), and rs1329428 (P = 0.0089), in CFH showed a significant association with wet AMD in the cohort of this study. A haplotype containing these four SNPs (CATA) significantly increased protection of wet AMD with a P value of 0.0005 and an odds ratio of 0.29 (95% confidence interval: 0.15-0.60). Unlike in other populations, rs2274700 and rs1410996 did not show a significant association with AMD in the Chinese population of this study. None of the SNPs in CFH showed a significant association with drusen, and none of the SNPs in CFH, C2, CFB, and C3 showed a significant association with either wet AMD or drusen in the cohort of this study. The CFHR1 and CFHR3 deletion was not polymorphic in the Chinese population and was not associated with wet AMD or drusen.

CONCLUSION

This study showed that SNPs rs3753394 (P = 0.0276), rs800292 (P = 0.0266), rs1061170 (P = 0.00514), and rs1329428 (P = 0.0089), but not rs7535263, rs1410996, or rs2274700, in CFH were significantly associated with wet AMD in a mainland Han Chinese population. This study showed that CFH was more likely to be AMD susceptibility gene at Chr.1q31 based on the finding that the CFHR1 and CFHR3 deletion was not polymorphic in the cohort of this study, and none of the SNPs that were significantly associated with AMD in a white population in C2, CFB, and C3 genes showed a significant association with AMD.

C-reactive protein and CFH, ARMS2/HTRA1 gene variants are independently associated with risk of macular degeneration

PURPOSE

Genetic variants CFH and ARMS2/HTRA1 gene regions as well as high-sensitivity C-reactive protein (CRP) levels are related to age-related macular degeneration (AMD). We evaluated their independent and combined effects on risk of AMD, as well as their interactions.

DESIGN

Case-control study.

PARTICIPANTS

Subjects with AMD (n = 244) or no or minimal maculopathy (n = 209) in the Age Related Eye Disease Ancillary Study.

METHODS

Risk factors, genotypes, and biomarkers were assessed by questionnaire, direct measurement, and analyses of blood specimens. The independent and joint effects of serum CRP and CFH (rs1061170) and ARMS2/HTRA1 (rs10490924) genotypes were assessed using logistic regression analyses, adjusting for age, gender, education, smoking, body mass index, and vitamin/mineral supplementation.

MAIN OUTCOME MEASURES

We defined AMD as large drusen, geographic atrophy, or neovascular disease.

RESULTS

Higher CRP levels were associated with a higher risk of AMD, controlling for genotype and demographic and behavioral risk factors, with odds ratio 2.6 for levels of 3.0 mg/L and above versus below 1.0 mg/L (95% confidence interval, 1.01-6.7). Single nucleotide polymorphisms (SNPs) in both genes were also independently associated with risk of AMD, controlling for the level of CRP and other factors. Presence of both highest level of CRP together with risk genotypes for both SNPs, conferred the highest risk of AMD (OR 5.4, 95% CI 1.4-21.1).

CONCLUSIONS

High-sensitivity CRP and polymorphisms in the CFH and ARMS2/HTRA1 genes are independently associated with risk of AMD. Higher CRP level tends to confer a higher risk of AMD within most genotype groups.

The molecular genetic basis of age-related macular degeneration: an overview

Age-related macular degeneration (AMD) is a complex disorder of the eye and the third leading cause of blindness worldwide. With a multifactorial etiology, AMD results in progressive loss of central vision affecting the macular region of the eye in elderly. While the prevalence is relatively higher in the Caucasian populations, it has gradually become a major public health issue among the non-Caucasian populations (including Indians) as well due to senescence, rapidly changing demographics and life-style factors. Recent genome-wide association studies (GWAS) on large case-control cohorts have helped in mapping genes in the complement cascade that are involved in the regulation of innate immunity with AMD susceptibility. Genes involved with mitochondrial oxidative stress and extracellular matrix regulation also play a role in AMD pathogenesis. Majority of the associations observed in complement (CFH, CFB, C2 and C3) and other (ARMS2 and HTRA1) genes have been replicated in diverse populations worldwide. Gene-gene (CFH with ARMS2 and HTRA1) interactions and correlations with environmental traits (smoking and body mass index) have been established as significant covariates in AMD pathology. In this review, we have provided an overview on the underlying molecular genetic mechanisms in AMD worldwide and highlight the AMD-associated-candidate genes and their potential role in disease pathogenesis.

Progression of geographic atrophy and genotype in age-related macular degeneration

PURPOSE

We sought to determine whether genotype is associated with rate of growth of geographic atrophy (GA) in eyes with age-related macular degeneration (AMD).

DESIGN

Prospective analysis of participants in a randomized controlled clinical trial.

PARTICIPANTS

We included 114 eyes of 114 participants in the Age-Related Eye Disease Study (AREDS).

METHODS

Fundus photographs from AREDS participants with GA from whom a DNA specimen had been obtained and serial photographs had been taken over a minimum of 2 years were evaluated for progression as determined by change in cumulative area of GA. All fundus photographs were scanned, digitized, and centrally graded longitudinally for area of GA. The relationship of GA progression with previously identified genetic variants associated with AMD was assessed.

MAIN OUTCOME MEASURES

Genotype frequencies and change in cumulative area of GA.

RESULTS

The mean growth rate of GA for the 114 eyes was 1.79 mm(2)/year (range, 0.17-4.76). No association between growth rate and genotype was present for variants in the CFH, C2, C3, APOE, and TLR3 genes. For the single nucleotide polymorphism rs10490924 in LOC387715/ARMS2, there was a significant association of GA growth rate, both adjusted and unadjusted for initial lesion size, with the homozygous risk genotype as compared with the homozygous nonrisk genotype (unadjusted P = 0.002; Bonferroni-corrected P = 0.014) and for allelic association (Bonferroni-corrected P value = 0.011). Analyses of other measures of GA progression (progression to central GA from extrafoveal GA and development of bilateral GA in those initially with unilateral GA) showed no statistically significant association between progression and the LOC387715/ARMS2/HTRA1 genotype.

CONCLUSIONS

Growth rates of GA calculated from digitized serial fundus photographs showed no association with variants in the CFH, C2, C3, APOE, or TLR3 genes. There was a nominally significant association with the LOC387715/ARMS2/HTRA1 genotype, although this finding was not supported by analyses of secondary measures of GA progression. Replication in other populations is needed to establish the existence of an association.

Complement, age-related macular degeneration and a vision of the future

Age-related macular degeneration (AMD) is one of the most well-characterized late-onset, complex trait diseases. Remarkable advances in our understanding of the genetic and biological foundations of this disease were derived from a recent convergence of scientific and clinical data. Importantly, the more recent identification of AMD-associated variations in a number of complement pathway genes has provided strong support for earlier, paradigm-shifting studies that suggested that aberrant function of the complement system plays a key role in disease etiology. Collectively, this wealth of information has provided an impetus for the development of powerful tools to accurately diagnose disease risk and progression and complement-based therapeutics that will ultimately delay or prevent AMD. Indeed, we are poised to witness a new era of a personalized approach toward the assessment, management, and treatment of this debilitating, chronic disease.

Vitreomacular adhesion in active and end-stage age-related macular degeneration

PURPOSE

To evaluate vitreomacular relations in different stages of age-related macular degeneration (AMD) without the influence of genetics and environmental factors.

DESIGN

Retrospective, observational case series.

METHODS

This was a multicenter study consisting of 29 previously untreated subjects with active exudative (wet) AMD in one eye and active nonexudative (dry) AMD in the fellow eye who were compared with 10 previously untreated subjects with end-stage geographic atrophy in one eye and an end-stage fibrotic (disciform) scar in the fellow eye. All subjects were studied with ultrasonography to identify the presence of posterior vitreous detachment (PVD) and by optical coherence tomography to detect vitreomacular adhesion (VMA).

RESULTS

The incidence of PVD in eyes with nonexudative AMD was 20 (69%) of 29, compared with 6 (21%) of 29 with active exudative AMD (P = .002). VMA was present in 11 (38%) of 29 of eyes with exudative AMD and in only 3 (10%) of 29 eyes with nonexudative AMD (P = .008). The incidence of PVD in geographic atrophy was 7 (70%) of 10, compared with 4 (40%) of 10 with disciform scar (P = .44). VMA was present in 2 (20%) of 10 eyes with disciform scars and in 0 (0%) of 10 eyes with geographic atrophy (P = .48).

CONCLUSIONS

PVD may protect against exudative AMD, whereas VMA may promote exudative AMD. This phenomenon is not evident in end-stage disease because of an increased incidence of PVD and a decreased incidence of VMA in eyes with disciform scars. Genetic and environmental factors do not seem to influence these observations.

Complement factor H and LOC387715 gene polymorphisms in a Greek population with age-related macular degeneration

BACKGROUND

Age-related macular degeneration (AMD) is the leading cause of severe visual loss among people over 60 years old. The lack of a broadly effective treatment for AMD underscores the need to identify causative biomarkers that could serve as preventive targets. Thus far, two major susceptibility loci for AMD have been identified, CFH T1277C and LOC387715 G270T. The primary goal of the present study was to elucidate whether these polymorphisms are major genetic determinants of AMD in a Greek population.

PATIENTS AND METHODS

A clinic-based, case-control association study was conducted, comprising 100 Greek patients with early and late-stage AMD and 115 independent controls of Caucasian origin. All participants underwent clinical examination including best-corrected visual acuity, intraocular pressure, and dilated fundus examination. Moreover, they were genotyped for CFH T1277C and LOC387715 G270T polymorphisms, by direct sequencing and ARMS PCR, respectively.

RESULTS

The frequency of the CFH 1277C allele was significantly higher in AMD patients in comparison with controls while the odds ratios (ORs) for AMD were 4.4-5.5. Statistical comparison of early and advanced AMD patients, on the basis of CFH genotype, revealed that the CFH 1277C allele was associated with both subgroups when compared with the controls (P < 0.001). When statistical comparison was performed between early and advanced patients on the basis of CFH genotypic frequencies, the CC genotype was found to be more prevalent in advanced AMD patients (P = 0.008, OR = 2.3). The frequency of the LOC387715 270 T allele was higher in AMD patients in comparison with controls (P < 0.04) while the ORs for AMD were 1.4-2. No statistically significant differences were located between the early AMD patients and controls, on the basis of LOC387715 genotype (P = 0.189). On the contrary, the T270G polymorphism was associated with advanced AMD (P = 0.04). Moreover, the TT genotype was more prevalent in patients with advanced AMD (P = 0.011, OR = 1.7) when compared with early AMD patients. Assessment of the combined contribution of CFH T1277C and LOC387715 G270T SNPs showed an independent manner of action of these polymorphisms in the development of the disease.

CONCLUSIONS

The replication of the reported associations of CFH T1277C polymorphism with AMD suggest that the 1277C 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 in the Greek population.

Combined effects of complement factor H genotypes, fish consumption, and inflammatory markers on long-term risk for age-related macular degeneration in a cohort

At baseline in 1992-1994, the authors assessed the combined effects of complement factor H (CFH) genotypes with smoking, fish consumption, and inflammatory markers on the risk of age-related macular degeneration (AMD) in 3,654 persons aged > or =49 years. They reexamined 75% of the survivors after 5 and 10 years, confirming incident AMD by side-by-side photographic grading. Of the 2,452 persons followed in the Blue Mountains Eye Study, 1,881 were genotyped (rs1061170), with CC, CT, and TT identified in 13.6%, 46.7%, and 39.7%, respectively. AMD risk increased with each additional C allele (early AMD: age- and sex-adjusted relative risk (RR) = 1.6, 95% confidence interval (CI): 1.2, 1.9; late AMD: RR = 2.3, 95% CI: 1.5, 3.6). Late AMD risk among current smokers with the CC/CT genotypes (RR = 10.7, 95% CI: 3.4, 33.9) was 5-fold that for genotypically similar nonsmokers (RR = 2.2, 95% CI: 0.9, 5.5) versus current nonsmokers with TT genotypes. Weekly compared with less than weekly consumption of fish was associated with reduced late AMD risk in participants with the CC genotype (RR = 0.15, 95% CI: 0.03, 0.8) but not the CT (RR = 0.7, 95% CI: 0.3, 2.0) or TT (RR = 1.3, 95% CI: 0.2, 7.2) genotypes. This study documents joint contributions from genetic and systemic factors in determining the progression of AMD.

Prediction model for prevalence and incidence of advanced age-related macular degeneration based on genetic, demographic, and environmental variables

PURPOSE

The joint effects of genetic, ocular, and environmental variables were evaluated and predictive models for prevalence and incidence of AMD were assessed.

METHODS

Participants in the multicenter Age-Related Eye Disease Study (AREDS) were included in a prospective evaluation of 1446 individuals, of which 279 progressed to advanced AMD (geographic atrophy or neovascular disease) and 1167 did not progress during 6.3 years of follow-up. For prevalent AMD, 509 advanced cases were compared with 222 controls. Covariates for the incidence analysis included age, sex, education, smoking, body mass index (BMI), baseline AMD grade, and the AREDS vitamin-mineral treatment assignment. DNA specimens were evaluated for six variants in five genes related to AMD. Unconditional logistic regression analyses were performed for prevalent and incident advanced AMD. An algorithm was developed and receiver operating characteristic curves and C statistics were calculated to assess the predictive ability of risk scores to discriminate progressors from nonprogressors.

RESULTS

All genetic polymorphisms were independently related to prevalence of advanced AMD, controlling for genetic factors, smoking, BMI, and AREDS treatment. Multivariate odds ratios (ORs) were 3.5 (95% confidence interval [CI], 1.7-7.1) for CFH Y402H; 3.7 (95% CI, 1.6-8.4) for CFH rs1410996; 25.4 (95% CI, 8.6-75.1) for LOC387715 A69S (ARMS2); 0.3 (95% CI, 0.1-0.7) for C2 E318D; 0.3 (95% CI, 0.1-0.5) for CFB; and 3.6 (95% CI, 1.4-9.4) for C3 R102G, comparing the homozygous risk/protective genotypes to the referent genotypes. For incident AMD, all these variants except CFB were significantly related to progression to advanced AMD, after controlling for baseline AMD grade and other factors, with ORs from 1.8 to 4.0 for presence of two risk alleles and 0.4 for the protective allele. An interaction was seen between CFH402H and treatment, after controlling for all genotypes. Smoking was independently related to AMD, with a multiplicative joint effect with genotype on AMD risk. The C statistic for the full model with all variables was 0.831 for progression to advanced AMD.

CONCLUSIONS

Factors reflective of nature and nurture are independently related to prevalence and incidence of advanced AMD, with excellent predictive power.

Multifactor effects and evidence of potential interaction between complement factor H Y402H and LOC387715 A69S in age-related macular degeneration

Background

Variants in the complement cascade genes and the LOC387715/HTRA1, have been widely reported to associate with age-related macular degeneration (AMD), the most common cause of visual impairment in industrialized countries.

Methods/Principal Findings

We investigated the association between the LOC387715 A69S and complement component C3 R102G risk alleles in the Finnish case-control material and found a significant association with both variants (OR 2.98, p = 3.75×10⁻⁹; non-AMD controls and OR 2.79, p = 2.78×10⁻¹⁹, blood donor controls and OR 1.83, p = 0.008; non-AMD controls and OR 1.39, p = 0.039; blood donor controls), respectively. Previously, we have shown a strong association between complement factor H (CFH) Y402H and AMD in the Finnish population. A carrier of at least one risk allele in each of the three susceptibility loci (LOC387715, C3, CFH) had an 18-fold risk of AMD when compared to a non-carrier homozygote in all three loci. A tentative gene-gene interaction between the two major AMD-associated loci, LOC387715 and CFH, was found in this study using a multiplicative (logistic regression) model, a synergy index (departure-from-additivity model) and the mutual information method (MI), suggesting that a common causative pathway may exist for these genes. Smoking (ever vs. never) exerted an extra risk for AMD, but somewhat surprisingly, only in connection with other factors such as sex and the C3 genotype. Population attributable risks (PAR) for the CFH, LOC387715 and C3 variants were 58.2%, 51.4% and 5.8%, respectively, the summary PAR for the three variants being 65.4%.

Conclusions/Significance

Evidence for gene-gene interaction between two major AMD associated loci CFH and LOC387715 was obtained using three methods, logistic regression, a synergy index and the mutual information (MI) index.

Age-related macular degeneration

Age-related macular degeneration is the leading cause of blindness in elderly populations of European descent. The most consistent risk factors associated with this ocular condition are increasing age and cigarette smoking. Genetic investigations have shown that complement factor H, a regulator of the alternative complement pathway, and LOC387715/HtrA1 are the most consistent genetic risk factors for age-related macular degeneration. Although the pathogenesis of this disease is unknown, oxidative stress might have an important role. Treatment with antioxidant vitamins and zinc can reduce the risk of developing advanced age-related macular degeneration by about a quarter in those at least at moderate risk. Intravitreal injections of ranibizumab, a monoclonal antibody that inhibits all forms of vascular endothelial growth factor, have been shown to stabilise loss of vision and, in some cases, improve vision in individuals with neovascular age-related macular degeneration. These findings, combined with assessments of possible environmental and genetic interactions and new approaches to modulate inflammatory pathways, will hopefully further expand our ability to understand and treat age-related macular degeneration.

Rhesus monkeys and humans share common susceptibility genes for age-related macular disease

Age-related macular degeneration (AMD), a complex multigenic disorder and the most common cause of vision loss in the elderly, is associated with polymorphisms in the LOC387715/ARMS2 and HTRA1 genes on 10q26. Like humans, macaque monkeys possess a macula and develop age-related macular pathologies including drusen, the phenotypic hallmark of AMD. We genotyped a cohort of 137 unrelated rhesus macaques with and without macular drusen. As in humans, one variant within LOC387715/ARMS2 and one in HTRA1 were significantly associated with affected status. HTRA1 and the predicted LOC387715/ARMS2 gene were both transcribed in rhesus and human retina and retinal pigment epithelium. Among several primate species, orthologous exons for the human LOC387715/ARMS2 gene were present only in Old World monkeys and apes. In functional analyses, the disease-associated HTRA1 polymorphism resulted in a 2-fold increase in gene expression, supporting a role in pathogenesis. These results demonstrate that two genes associated with AMD in humans are also associated with macular disease in rhesus macaques and that one of these genes is specific to higher primates. This is the first evidence that humans and macaques share the same genetic susceptibility factors for a common complex disease.

Smoking and the risk of age-related macular degeneration: a meta-analysis

PURPOSE

Some studies were undertaken to evaluate the association between cigarette smoking and age-related macular degeneration (AMD). This meta-analysis summarized the risk estimate of smoking and AMD and provided robust evidence for the association.

METHODS

Relevant studies were identified by searching PubMed and MEDLINE (from 1966 to June 2007) and reviewing the reference lists of key articles. The summary relative risk ratio (RR) or odds ratio (OR) and 95% confidence interval (CI) were calculated. Study-specific risk estimates were pooled using a random-effects model.

RESULTS

Five prospective cohort and eight case-control studies met our inclusion criteria. Ever smoking was statistically significant associated with increased risk of AMD among cohort studies (RR, 1.61; 95% CI, 1.01-2.57) or case-control studies (RR, 1.76; 95% CI, 1.56-1.99). Current smokers were at higher risk of AMD than past smokers. Both geographic atrophy (GA) and neovascular AMD (NV) are subtypes of AMD. A significant relationship was found between smoking and GA risk. Smoking increased the risk of NV, with marginal nonsignificance (RR, 1.47; 95% CI, 0.92-2.37) in cohort studies and significance in case-control studies (RR, 1.96; 95% CI, 1.69-2.27).

CONCLUSIONS

This meta-analysis indicated smoking, especially current smoking, was significantly associated with increased risks of AMD and its subtypes.

HTRA1 variants in exudative age-related macular degeneration and interactions with smoking and CFH

PURPOSE

Mapping the genes for age-related macular degeneration (AMD) had not been successful until recent genome-wide association studies revealed Tyr402His in CFH and rs11200638 in HTRA1 as AMD-related genetic variants. This study was conducted to identify other critical factors in HTRA1 that are associated with exudative AMD.

METHODS

The promoter, splice regions, and coding exons of HTRA1 were sequenced in 163 patients with exudative AMD and 183 sex- and age-matched control subjects. Also documented were the CFH genotype and smoking status.

RESULTS

Four significant SNPs were found in the promoter and the first exon of HTRA1: rs11200638 (-625G>A), rs2672598 (-487T>C), rs1049331 (102C>T, Ala34Ala), and rs2293870 (108G>T, Gly36Gly) with respective P = 1.7 x 10(-14), 3.0 x 10(-10), 3.7 x 10(-12), and 3.7 x 10(-12). Among them, rs11200638 is the most significant associated SNP with a high odds ratio (OR) of 7.6 (95% CI: 3.94-14.51). One risk haplotype block across the promoter and exon 1, ACCTT, significantly predisposes to AMD (P = 6.68 x 10(-14)). In both models, significant independent additive effects were identified with smoking and rs800292 (184G>A, Val62Ile) of CFH. Smoking and rs11200638 (HTRA1) combined caused a 15.7-fold increased risk, whereas combined rs800292 and rs11200638 caused a 23.3-fold increased risk. An extremely high population attributable risk (PAR) of 78% was also found.

CONCLUSIONS

A high impact of the additive effect of CFH and HTRA1 in the development of exudative AMD was shown. The HTRA1-smoking additive effect found in this study further suggests the importance of this environmental risk factor in AMD.

C2 and CFB genes in age-related maculopathy and joint action with CFH and LOC387715 genes

Background

Age-related maculopathy (ARM) is a common cause of visual impairment in the elderly populations of industrialized countries and significantly affects the quality of life of those suffering from the disease. Variants within two genes, the complement factor H (CFH) and the poorly characterized LOC387715 (ARMS2), are widely recognized as ARM risk factors. CFH is important in regulation of the alternative complement pathway suggesting this pathway is involved in ARM pathogenesis. Two other complement pathway genes, the closely linked complement component receptor (C2) and complement factor B (CFB), were recently shown to harbor variants associated with ARM.

Methods/Principal Findings

We investigated two SNPs in C2 and two in CFB in independent case-control and family cohorts of white subjects and found rs547154, an intronic SNP in C2, to be significantly associated with ARM in both our case-control (P-value 0.00007) and family data (P-value 0.00001). Logistic regression analysis suggested that accounting for the effect at this locus significantly (P-value 0.002) improves the fit of a genetic risk model of CFH and LOC387715 effects only. Modeling with the generalized multifactor dimensionality reduction method showed that adding C2 to the two-factor model of CFH and LOC387715 increases the sensitivity (from 63% to 73%). However, the balanced accuracy increases only from 71% to 72%, and the specificity decreases from 80% to 72%.

Conclusions/Significance

C2/CFB significantly influences AMD susceptibility and although accounting for effects at this locus does not dramatically increase the overall accuracy of the genetic risk model, the improvement over the CFH-LOC387715 model is statistically significant.

Phenotype analysis of patients with the risk variant LOC387715 (A69S) in age-related macular degeneration

PURPOSE

To examine phenotypes of age-related macular degeneration (AMD) patients with the LOC387715 variant (T allele at rs10490924, A69S).

DESIGN

Retrospective, observational case series.

METHODS

This clinic-based case series data set contained 775 unrelated cases of AMD. AMD phenotypes of three groups, determined by the number of LOC387715 risk alleles, were compared regarding the presence or absence of 16 phenotypic features.

RESULTS

The number of AMD cases in each group was 164 cases (two risk alleles), 330 cases (one risk allele), and 281 cases (zero risk allele). The mean age at examination for homozygous carriers of the LOC387715 risk allele was significantly lower (73.9 years) than the age for carriers of one (76.4 years) or no (77.1 years) risk allele (P = .0003). Of the 16 features analyzed, only AMD grade (P = .00002) was significantly associated with the LOC387715 variant. As the number of LOC387715 risk alleles increased, the proportion of grade 5 AMD cases increased in a dose-response fashion.

CONCLUSIONS

The LOC387715 variant appears to be an independent risk factor for grade 5 (neovascular) AMD. This variant may also be associated with an earlier onset of AMD. Phenotypes that suggest a high-risk genotype may prove valuable for diagnostic, therapeutic, and research purposes.

Deletion of CFHR3 and CFHR1 genes in age-related macular degeneration

Age-related macular degeneration (AMD) impairs vision for approximately 7.5 million Americans. Both susceptibility variants and protective haplotypes in the complement factor H (CFH) gene modulate risk for AMD. Recently, deletion of the 'CFH-related' genes CFHR1 and CFHR3 was found to be segregating with a particular CFH haplotype, which reduced the risk of AMD. We tested the deletion for association in a Caucasian population of 780 cases and 265 controls and examined its effect in the context of known AMD risk factors. The deletion did not segregate perfectly with any one SNP, as previously suggested. CFH haplotype P2 was the most frequent haplotype in deletion homozygotes (47%), and the majority (14/16) of these individuals were homozygous for the non-risk allele of Y402H. Overall, deletion homozygosity was significantly more frequent in controls than cases (2.6% controls, 0.8% cases, P = 0.025, OR = 0.29, 95% CI = 0.10-0.86). After controlling for age, Y402H, smoking and LOC387715 A69S, the protective effect of the deletion was no longer statistically significant (P = 0.27). However, using a CFH haplotype that all deletion homozygotes share as a surrogate for the deletion, this marker remained modestly associated with AMD after adjustment for known risk factors (OR = 0.63, 95% CI 0.39-1.04, P = 0.07). Therefore, deletion of CFHR1 and CFHR3 may account for a small portion of the protection from AMD associated with particular haplotypes in CFH. The presence of protective haplotypes in CFH that do not carry the deletion, suggests that other protective variants in this region have yet to be discovered.

Posterior vitreomacular adhesion: a potential risk factor for exudative age-related macular degeneration?

PURPOSE

To compare the state of the posterior vitreous in exudative age-related macular degeneration (AMD) with eyes with nonexudative AMD and controls.

DESIGN

Prospective, observational case series.

METHODS

B-scan ultrasonography and optical coherence tomography (OCT) were performed in 163 eyes from 82 subjects older than 55 years, 50 eyes with exudative AMD, 57 with nonexudative AMD, and 56 control eyes. Main outcome measures were the number of eyes with complete posterior vitreous detachment (PVD) by ultrasound and the number of eyes with central vitreomacular adhesion by OCT.

RESULTS

By ultrasonography, 17 (34.0%) of 50 eyes with exudative AMD had PVD as compared with 41 (71.9%) of 57 eyes with nonexudative AMD (P = .00002) and 34 (60.7%) of 56 controls (P = .017). OCT detected persistent central vitreoretinal adhesion surrounded by a detached posterior vitreous cortex in 18 (36%) of 50 eyes with exudative AMD, significantly higher than in nonexudative AMD (4/57 [7%]; P < .0001) and in controls (6/56 [10%]; P = .002).

CONCLUSIONS

Persistent attachment of the posterior vitreous cortex to the macula may be another risk factor for the development of exudative AMD via vitreoretinal traction inducing chronic low-grade inflammation, by maintaining macular exposure to cytokines or free radicals in the vitreous gel, or by interfering in transvitreous oxygenation and nutrition of the macula. Inducing PVD may provide prophylactic benefit against exudative AMD.

The LOC387715 polymorphism, inflammatory markers, smoking, and age-related macular degeneration. A population-based case-control study

OBJECTIVE

To assess combined effects on the risk of age-related macular degeneration (AMD) by the LOC387715 polymorphism, smoking, and inflammatory or hemostatic factors.

DESIGN

Population-based case-control study.

PARTICIPANTS

Two hundred seventy-eight AMD cases (224 early, 54 late) and 557 controls matched for age, gender, and smoking, drawn from the Blue Mountains Eye Study cohort.

METHODS

Subjects were genotyped for the LOC387715 Ala69Ser polymorphism (rs# 10490924). Smoking was self-reported. Serum high-sensitivity C-reactive protein (CRP), interleukin 6 (IL-6), soluble intercellular adhesion molecule 1 (sICAM-1), fibrinogen, homocysteine, plasminogen activator inhibitor 1 (PAI-1), von Willebrand factor, and white cell count (WCC) were measured. Combined effects of this genetic variant plus any of these study factors on AMD risk were assessed using logistic regression models, adjusted for age and smoking. We defined interaction if the influence of 2 factors departed from the multiplicative scale, confirmed by a statistically significant interaction term. Otherwise, the combined effect was used.

MAIN OUTCOME MEASURES

Age-related macular degeneration was graded using the Wisconsin grading system.

RESULTS

Combined effects on the likelihood of early or late AMD were demonstrated for the LOC387715 Ala69Ser G/T and T/T genotypes with the markers high-sensitivity CRP (odds ratios [ORs], 1.2 for the highest tertile alone, 1.6 for G/T and T/T genotypes alone, and 2.2 for both G/T and T/T genotypes plus the highest tertile, compared with the G/G genotype with the 2 lower tertiles), IL-6 (corresponding ORs, 1.1, 1.6, and 2.2), sICAM-1 (ORs, 1.0, 1.5, and 2.3, respectively), and PAI-1 (ORs, 1.3, 1.7, and 2.3, respectively), but not with WCC, fibrinogen, homocysteine, and von Willebrand factor. Findings were similar for early and late AMD separately. Current smokers with G/T and T/T genotypes had strong combined effects on late AMD risk compared with those who never smoked or past smokers with the G/G genotype (ORs, 1.2 for current smokers alone, 1.8 for G/T and T/T genotypes alone, and 6.1 for current smokers plus G/T and T/T genotypes).

CONCLUSIONS

We found no significant interaction but combined effects for the LOC387715 genotypes with 3 inflammatory markers and PAI-1 on the risk of early or late AMD, and with current smoking on the risk of late AMD.