Nonsynonymous single nucleotide polymorphisms in the complement component 3 gene are associated with risk of age-related macular degeneration: a meta-analysis

Genetic and Epigenetic Biomarkers Linking Alzheimer's Disease and Age-Related Macular Degeneration

Alzheimer's disease (AD) represents a prominent neurodegenerative disorder (NDD), accounting for the majority of dementia cases worldwide. In addition to memory deficits, individuals with AD also experience alterations in the visual system. As the retina is an extension of the central nervous system (CNS), the loss in retinal ganglion cells manifests clinically as decreased visual acuity, narrowed visual field, and reduced contrast sensitivity. Among the extensively studied retinal disorders, age-related macular degeneration (AMD) shares numerous aging processes and risk factors with NDDs such as cognitive impairment that occurs in AD. Histopathological investigations have revealed similarities in pathological deposits found in the retina and brain of patients with AD and AMD. Cellular aging processes demonstrate similar associations with organelles and signaling pathways in retinal and brain tissues. Despite these similarities, there are distinct genetic backgrounds underlying these diseases. This review comprehensively explores the genetic similarities and differences between AMD and AD. The purpose of this review is to discuss the parallels and differences between AMD and AD in terms of pathophysiology, genetics, and epigenetics.

Genetic Aspects of Age-Related Macular Degeneration and Their Therapeutic Potential

Age-related macular degeneration (AMD) is a complex and multifactorial disease, resulting from the interaction of environmental and genetic factors. The continuous discovery of associations between genetic polymorphisms and AMD gives reason for the pivotal role attributed to the genetic component to its development. In that light, genetic tests and polygenic scores have been created to predict the risk of development and response to therapy. Still, none of them have yet been validated. Furthermore, there is no evidence from a clinical trial that the determination of the individual genetic structure can improve treatment outcomes. In this comprehensive review, we summarize the polymorphisms of the main pathogenetic ways involved in AMD development to identify which of them constitutes a potential therapeutic target. As complement overactivation plays a major role, the modulation of targeted complement proteins seems to be a promising therapeutic approach. Herein, we summarize the complement-modulating molecules now undergoing clinical trials, enlightening those in an advanced phase of trial. Gene therapy is a potential innovative one-time treatment, and its relevance is quickly evolving in the field of retinal diseases. We describe the state of the art of gene therapies now undergoing clinical trials both in the field of complement-suppressors and that of anti-VEGF.

The Role of Oxidative Stress and the Importance of miRNAs as Potential Biomarkers in the Development of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is the primary cause of blindness in developed countries. With the progressive aging of the population, AMD is a significant ophthalmological problem in the population over 50 years of age. The etiology of AMD is known to be based on various biochemical, immunological and molecular pathways and to be influenced by a range of genetic and environmental elements. This review provides an overview of the pathophysiological role of oxidative stress and free radicals in the retina with a special focus on the DNA repair efficiency and enzymatic antioxidant defense. It also presents a correlation between miRNA profile and AMD, and indicates their involvement in inflammation, angiogenesis, increased oxidation of cellular components, enzymatic antioxidant capacity and DNA repair efficiency, which play particularly important roles in AMD pathogenesis. Gene silencing by miRNAs can induce changes in antioxidant enzymes, leading to a complex interplay between redox imbalance by free radicals and miRNAs in modulating cellular redox homeostasis.

Complement System and Potential Therapeutics in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a complex multifactorial disease characterized in its late form by neovascularization (wet type) or geographic atrophy of the retinal pigment epithelium cell layer (dry type). The complement system is an intrinsic component of innate immunity. There has been growing evidence that the complement system plays an integral role in maintaining immune surveillance and homeostasis in AMD. Based on the association between the genotypes of complement variants and AMD occurrence and the presence of complement in drusen from AMD patients, the complement system has become a therapeutic target for AMD. However, the mechanism of complement disease propagation in AMD has not been fully understood. This concise review focuses on an overall understanding of the role of the complement system in AMD and its ongoing clinical trials. It provides further insights into a strategy for the treatment of AMD targeting the complement system.

Complement family member CFI polymorphisms and AMD susceptibility from a comprehensive analysis

The complement factor I (CFI) gene polymorphisms have been reported to age-related macular degenerative (AMD) risk, nevertheless, above association is not consistent. We investigated a meta-analysis to evaluate the conclusions between CFI polymorphisms (rs10033900 and rs2285714) and AMD risk. An identification was covered with the PubMed and other databases through February 8, 2020. Odds ratios (OR) and 95% confidence intervals (CI) were used to assess the strength of associations. After a comprehensive search, 11 different articles (12 case–control studies for total AMD and 11 case–control studies about neovascular disease/geographic atrophy in AMD) were retrieved. Individuals carrying C-allele or CC genotype of rs10033900 polymorphism may have a decreased risk to be AMD disease. For example, there has a significantly decreased relationship between rs10033900 polymorphism and AMD both in the whole group, Caucasian population and population-based source of control. Moreover, a similar trend in subgroup of genotype method group by MALDI-TOF MS was detected. To classify the type of AMD in further, decreased association was also observed in both neovascular disease and geographic atrophy AMD. No association was found about rs2285714 polymorphism. Our present groundbreaking study suggests that the CFI rs10033900 polymorphism is potentially associated with the risk of AMD development.

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 genetic variation of complement C3 and the susceptibility to advanced age-related macular degeneration: a meta-analysis

BACKGROUND

The purpose of this study is to discuss whether genetic variants (rs2230199, rs1047286, rs2230205, and rs2250656) in the C3 gene account for a significant risk of advanced AMD.

METHODS

We performed a meta-analysis using electronic databases to search relevant articles. A total of 40 case-control studies from 38 available articles (20,673 cases and 20,025 controls) were included in our study.

RESULTS

In our meta-analysis, the pooled results showed that the carriage of G allele for rs2230199 and the T allele for rs1047286 had a tendency to the risk of advanced AMD (OR = 1.49, 95% CI = 1.39-1.59, P < 0.001; OR = 1.45, 95% CI = 1.37-1.54, P < 0.001). Moreover, in the subgroup analysis based on ethnicity, rs2230199 and rs1047286 polymorphisms were more likely to be a predictor of response for Caucasian region (OR = 1.48, 95% CI = 1.38-1.59, P < 0.001; OR = 1.45, 95% CI = 1.37-1.54, P < 0.001). Besides, pooled results suggested that the G allele of rs2230199 could confer susceptibility to advanced AMD in Middle East (OR = 1.62, 95% CI = 1.33-1.97, P < 0.001).

CONCLUSION

In our meta-analysis, C3 genetic polymorphisms unveiled a positive effect on the risk of advanced AMD, especially in Caucasians. Furthermore, numerous well-designed studies with large sample-size are required to validate this conclusion.

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.

Complement System and Age-Related Macular Degeneration: Implications of Gene-Environment Interaction for Preventive and Personalized Medicine

Age-related macular degeneration (AMD) is the most common cause of visual loss in developed countries, with a significant economic and social burden on public health. Although genome-wide and gene-candidate studies have been enabled to identify genetic variants in the complement system associated with AMD pathogenesis, the effect of gene-environment interaction is still under debate. In this review we provide an overview of the role of complement system and its genetic variants in AMD, summarizing the consequences of the interaction between genetic and environmental risk factors on AMD onset, progression, and therapeutic response. Finally, we discuss the perspectives of current evidence in the field of genomics driven personalized medicine and public health.

Age-Related Macular Degeneration: Genetics and Biology

Age-related macular degeneration (AMD), widely prevalent across the globe, is a major stakeholder among adult visual morbidity and blindness, not only in the Western world but also in Asia. Several risk factors have been identified, including critical genetic factors, which were never imagined 2 decades ago. The etiopathogenesis is emerging to demonstrate that immune and complement-related inflammation pathway members chronically exposed to environmental insults could justifiably influence disease morbidity and treatment outcomes. Approximately half a dozen physiological and biochemical cascades are disrupted in the AMD disease genesis, eventually leading to the distortion and disruption of the subretinal space, subretinal pigment epithelium, and Bruch membrane, thus setting off chaos and disorder for signs and symptoms to manifest. Approximately 3 dozen genetic factors have so far been identified, including the recent ones, through powerful genomic technologies and large robust sample sizes. The noteworthy genetic variants (common and rare) are complement factor H, complement factor H-related genes 1 to 5, C3, C9, ARMS2/HTRA1, vascular endothelial growth factor A, vascular endothelial growth factor receptor 2/KDR, and rare variants (show causal link) such as TIMP3, fibrillin, COL4A3, MMP19, and MMP9. Despite the enormous amount of scientific information generated over the years, diagnostic genetic or biomarker tests are still not available for clinicians to understand the natural course of the disease and its management in a patient. However, further research in the field should reduce this gap not only by aiding the clinician but also through the possibilities of clinical intervention with complement pathway-related inhibitors entering preclinical and clinical trials in the near future.

Risk factors and biomarkers of age-related macular degeneration

A biomarker can be a substance or structure measured in body parts, fluids or products that can affect or predict disease incidence. As age-related macular degeneration (AMD) is the leading cause of blindness in the developed world, much research and effort has been invested in the identification of different biomarkers to predict disease incidence, identify at risk individuals, elucidate causative pathophysiological etiologies, guide screening, monitoring and treatment parameters, and predict disease outcomes. To date, a host of genetic, environmental, proteomic, and cellular targets have been identified as both risk factors and potential biomarkers for AMD. Despite this, their use has been confined to research settings and has not yet crossed into the clinical arena. A greater understanding of these factors and their use as potential biomarkers for AMD can guide future research and clinical practice. This article will discuss known risk factors and novel, potential biomarkers of AMD in addition to their application in both academic and clinical settings.

Complement 3 and metabolic syndrome induced by clozapine: a cross-sectional study and retrospective cohort analysis

Metabolic syndrome (MetS) is considered to be an adverse effect of long-term treatment with atypical antipsychotics, particularly clozapine. There is strong evidence that the activation of inflammatory pathways interferes with normal metabolism and contributes to the development of MetS. C3, which is an inflammation molecule, has been reported to be associated with MetS. Because C3 is a heritable trait, we accordingly hypothesized that the gene encoding C3 (C3) would be a candidate gene for inter-individual variation in clozapine-induced MetS. We recruited 576 schizophrenia patients taking clozapine and measured the serum levels of fasting metabolic parameters. We then examined C3 mRNA and genotyped seven polymorphisms in C3. The expression quantitative trait locus (eQTL) data available for tissues were extracted by the Genotype-Tissue Expression Portal. A total of 105 patients' medical records were retrospectively reviewed to obtain the metabolic parameters during the initial 2-year clozapine treatment. The relative expression levels of C3 mRNA in patients with MetS were significantly higher than in those without MetS (P=0.02). C3 single-nucleotide polymorphism (SNP) rs2277984 was marginally associated with MetS (allelic P=0.06, odds ratio=1.36, 95% confidence interval (CI): 1.07-1.72). We found a significant association of rs2277984 with fasting triglyceride (TG) levels (P=0.004). Further, eQTL analysis revealed that rs2277984 regulates C3 expression in the liver (P=0.002). Similar results were found in the retrospective cohort analysis. The receiver operating characteristic curve showed a significant effect of the rs2277984 G allele on the percentage change of TG levels, with an area under the curve of 0.71 (95% CI: 0.60-0.81). C3 is likely to enhance TG accumulation and to confer susceptibility to clozapine-induced MetS. The C3 SNP rs2277984 may be a potential biomarker for predicting MetS risk in patients receiving clozapine treatment.

A Preliminary Genetic Analysis of Complement 3 Gene and Schizophrenia

Complement pathway activation was found to occur frequently in schizophrenia, and complement 3 (C3) plays a major role in this process. Previous studies have provided evidence for the possible role of C3 in the development of schizophrenia. In this study, we hypothesized that the gene encoding C3 (C3) may confer susceptibility to schizophrenia in Han Chinese. We analyzed 7 common single nucleotide polymorphisms (SNPs) of C3 in 647 schizophrenia patients and 687 healthy controls. Peripheral C3 mRNA expression level was measured in 23 drug-naïve patients with schizophrenia and 24 controls. Two SNPs (rs1047286 and rs2250656) that deviated from Hardy-Weinberg equilibrium were excluded for further analysis. Among the remaining 5 SNPs, there was no significant difference in allele and genotype frequencies between the patient and control groups. Logistic regression analysis showed no significant SNP-gender interaction in either dominant model or recessive model. There was no significant difference in the level of peripheral C3 expression between the drug-naïve schizophrenia patients and healthy controls. In conclusion, the results of this study do not support C3 as a major genetic susceptibility factor in schizophrenia. Other factors in AP may have critical roles in schizophrenia and be worthy of further investigation.