Whole-exome sequencing identifies rare, functional CFH variants in families with macular degeneration

Whole genome sequencing of 4,787 individuals identifies gene-based rare variants in age-related macular degeneration

Genome-wide association studies have contributed extensively to the discovery of disease-associated common variants. However, the genetic contribution to complex traits is still largely difficult to interpret. We report a genome-wide association study of 2394 cases and 2393 controls for age-related macular degeneration (AMD) via whole-genome sequencing, with 46.9 million genetic variants. Our study reveals significant single-variant association signals at four loci and independent gene-based signals in CFH, C2, C3, and NRTN. Using data from the Exome Aggregation Consortium (ExAC) for a gene-based test, we demonstrate an enrichment of predicted rare loss-of-function variants in CFH, CFI, and an as-yet unreported gene in AMD, ORMDL2. Our method of using a large variant list without individual-level genotypes as an external reference provides a flexible and convenient approach to leverage the publicly available variant datasets to augment the search for rare variant associations, which can explain additional disease risk in AMD.

Risk and protection of different rare protein-coding variants of complement component C4A in age-related macular degeneration

Introduction: Age-related macular degeneration (AMD) is the leading cause of central vision loss in the elderly. One-third of the genetic contribution to this disease remains unexplained. Methods: We analyzed targeted sequencing data from two independent cohorts (4,245 cases, 1,668 controls) which included genomic regions of known AMD loci in 49 genes. Results: At a false discovery rate of <0.01, we identified 11 low-frequency AMD variants (minor allele frequency <0.05). Two of those variants were present in the complement C4A gene, including the replacement of the residues that contribute to the Rodgers-1/Chido-1 blood group antigens: [VDLL1207-1210ADLR (V1207A)] with discovery odds ratio (OR) = 1.7 (p = 3.2 × 10-5) which was replicated in the UK Biobank dataset (3,294 cases, 200,086 controls, OR = 1.52, p = 0.037). A novel variant associated with reduced risk for AMD in our discovery cohort was P1120T, one of the four C4A-isotypic residues. Gene-based tests yielded aggregate effects of nonsynonymous variants in 10 genes including C4A, which were associated with increased risk of AMD. In human eye tissues, immunostaining demonstrated C4A protein accumulation in and around endothelial cells of retinal and choroidal vasculature, and total C4 in soft drusen. Conclusion: Our results indicate that C4A protein in the complement activation pathways may play a role in the pathogenesis of AMD.

Whole Genome Sequencing Identifies Novel Common and Low-Frequency Variants Associated With Age-Related Macular Degeneration

Purpose

To identify associations of common, low-frequency, and rare variants with advanced age-related macular degeneration (AMD) using whole genome sequencing (WGS).

Methods

WGS data were obtained for 2123 advanced AMD patients (participants of clinical trials for advanced AMD) and 2704 controls (participants of clinical trials for asthma [N = 2518] and Alzheimer's disease [N = 186]), and joint genotype calling was performed, followed by quality control of the dataset. Single variant association analyses were performed for all identified common, low-frequency, and rare variants. Gene-based tests were executed for rare and low-frequency variants using SKAT-O and three groups of variants based on putative impact information: (1) all variants, (2) modifier impact variants, and (3) high- and moderate-impact variants. To ascertain independence of the identified associations from previously reported AMD and asthma loci, conditional analyses were performed.

Results

Previously identified AMD variants at the CFH, ARMS2/HTRA1, APOE, and C3 loci were associated with AMD at a genome-wide significance level. We identified new single variant associations for common variants near the PARK7 gene and in the long non-coding RNA AC103876.1, and for a rare variant near the TENM3 gene. In addition, gene-based association analyses identified a burden of modifier variants in eight intergenic and gene-spanning regions and of high- and moderate-impact variants in the C3, CFHR5, SLC16A8, and CFI genes.

Conclusions

We describe the largest WGS study in AMD to date. We confirmed previously identified associations and identified several novel associations that are worth exploring in further follow-up studies.

Identification of complement factor H variants that predispose to pre-eclampsia: A genetic and functional study

OBJECTIVE

The objective of the study was to investigate the role of genetic variants in complement proteins in pre-eclampsia.

DESIGN

In a case-control study involving 609 cases and 2092 controls, five rare variants in complement factor H (CFH) were identified in women with severe and complicated pre-eclampsia. No variants were identified in controls.

SETTING

Pre-eclampsia is a leading cause of maternal and fetal morbidity and mortality. Immune maladaptation, in particular, complement activation that disrupts maternal-fetal tolerance leading to placental dysfunction and endothelial injury, has been proposed as a pathogenetic mechanism, but this remains unproven.

POPULATION

We genotyped 609 pre-eclampsia cases and 2092 controls from FINNPEC and the national FINRISK cohorts.

METHODS

Complement-based functional and structural assays were conducted in vitro to define the significance of these five missense variants and each compared with wild type.

MAIN OUTCOME MEASURES

Secretion, expression and ability to regulate complement activation were assessed for factor H proteins harbouring the mutations.

RESULTS

We identified five heterozygous rare variants in complement factor H (L3V, R127H, R166Q, C1077S and N1176K) in seven women with severe pre-eclampsia. These variants were not identified in controls. Variants C1077S and N1176K were novel. Antigenic, functional and structural analyses established that four (R127H, R166Q, C1077S and N1176K) were deleterious. Variants R127H and C1077S were synthesised, but not secreted. Variants R166Q and N1176K were secreted normally but showed reduced binding to C3b and consequently defective complement regulatory activity. No defect was identified for L3V.

CONCLUSIONS

These results suggest that complement dysregulation due to mutations in complement factor H is among the pathophysiological mechanisms underlying severe pre-eclampsia.

Rare Dysfunctional Complement Factor I Genetic Variants and Progression to Advanced Age-Related Macular Degeneration

Purpose

To evaluate associations between rare dysfunctional complement factor I (CFI) genetic variant status and progression to advanced age-related macular degeneration (AAMD), geographic atrophy (GA), and neovascular disease (NV).

Design

Prospective, longitudinal study.

Participants

Patients aged 55 to 80 years at baseline identifying as White with non-AAMD in 1 or both eyes at baseline were included. Follow-up grades were assigned as early, intermediate, or AAMD (GA or NV). CFI variants were categorized using genotyping and sequencing platforms.

Methods

Analyses were performed using the Seddon Longitudinal Cohort Study (N = 2116 subjects, 3901 eyes, and mean follow-up of 8.3 years) and the Age-Related Eye Disease Study (N = 2837 subjects, 5200 eyes, and mean follow-up of 9.2 years). CFI rare variants associated with low serum factor I (FI) protein levels and decreased FI function (type 1), other AMD genetic variants, and demographic, behavioral, and ocular factors were evaluated. Generalized estimating equations methods were used to assess the association between CFI rare variants and progression, independent of other genetic variants and covariates.

Main Outcome Measures

Progression to AAMD, GA, or NV.

Results

In the prospective cohort of 4953 subjects (9101 eyes with non-AAMD at baseline), 1% were type 1 rare CFI carriers. Over 12 years, progression to AAMD was 44% for carriers and 20% for noncarriers (P < 0.001), 30% of carriers versus 10% of noncarriers progressed to GA (P < 0.001), and 18% of carriers compared with 11% of noncarriers progressed to NV (P = 0.049). CFI carriers were more likely to have a family history of AMD (P for trend = 0.035) and a higher baseline AMD grade (P < 0.001). After adjusting for all covariates, CFI carrier status was associated with progression to GA (odds ratio [OR] = 1.91; 95% confidence interval [CI] = 1.03, 3.52) but not NV (OR = 0.96). Higher body mass index was associated with progression among CFI carriers (body mass index ≥ 25 vs. < 25; OR = 5.8; 95% CI 1.5, 22.3) but not for noncarriers (OR = 1.1; 95% CI = 0.9, 1.3), with P_interaction = 0.011.

Conclusions

Results suggest that carriers of rare dysfunctional type 1 CFI variants are at higher risk for progression to AAMD with GA.

Financial Disclosures

Proprietary or commercial disclosure may be found after the references.

Identifying Novel Genes and Variants in Immune and Coagulation Pathways Associated with Macular Degeneration

Purpose

To select individuals and families with a low genetic burden for age-related macular degeneration (AMD), to inform the clinical diagnosis of macular disorders, and to find novel genetic variants associated with maculopathies.

Design

Genetic association study based on targeted and whole-exome sequencing.

Participants

A total of 758 subjects (481 individuals with maculopathy and 277 controls), including 316 individuals in 72 families.

Methods

We focused on 150 genes involved in the complement, coagulation, and inflammatory pathways. Single-variant tests were performed on 7755 variants shared among ≥ 5 subjects using logistic regression. Gene-based tests were used to evaluate aggregate effects from rare and low-frequency variants (at minor allele frequency [MAF] ≤ 5% or ≤ 1%) in a gene using burden tests. For families whose affected members had a low burden of genetic risk based on known common and rare variants related to AMD, we searched for rare variants (MAF < 0.001) whose risk alleles occurred in ≥ 80% of affected individuals but not in controls. Immunohistochemistry was performed to determine the protein expression of a novel gene (coagulation factor II thrombin receptor-like 2 [F2RL2]) in retinal tissues.

Main Outcome Measures

Genotypes and phenotypes of macular degeneration.

Results

We confirmed the association of a synonymous variant in complement factor H (Ala473, rs2274700, proxy to intronic rs1410996, r 2  = 1) with maculopathy (odds ratio, 0.64; P = 4.5 × 10-4). Higher AMD polygenic risk scores (PRSs) were associated with intermediate and advanced AMD. Among families with low PRSs and no known rare variants for maculopathy, we identified 2 novel, highly penetrant missense rare variants in ADAM15, A disintegrin and metalloprotease, metallopeptidase domain 15 (p.Arg288Cys) and F2RL2 (p.Leu289Arg). Immunohistochemistry analyses revealed F2RL2 protein expression in cone photoreceptor outer segments and Müller glia cells of human and pig retinas. Coagulation factor II thrombin receptor-like 2 expression appeared increased in fibrotic areas in advanced AMD samples with neovascularization, suggesting that F2RL2 may play a role in the progression to advanced macular disease.

Conclusions

New missense rare variants in the genes ADAM15 and F2RL2 were associated with maculopathies. Results suggest that novel genes related to the coagulation and immune pathways may be involved in the pathogenesis of macular diseases.

Latest Development on Genetics of Common Retinal Diseases

Many complex forms of retinal diseases are common and pan-ethnic in occurrence. Among them, neovascular age-related macular degeneration, polypoidal choroidal vasculopathy, and central serous choroid retinopathy involve both choroidopathy and neovascularization with multifactorial etiology. They are sight-threatening and potentially blinding. Early treatment is crucial to prevent disease progression. To understand their genetic basis, candidate gene mutational and association analyses, linkage analysis, genome-wide association studies, transcriptome analysis, next-generation sequencing, which includes targeted deep sequencing, whole-exome sequencing, and whole genome sequencing have been conducted. Advanced genomic technologies have led to the identification of many associated genes. But their etiologies are attributed to complicated interactions of multiple genetic and environmental risk factors. Onset and progression of neovascular age-related macular degeneration and polypoidal choroidal vasculopathy are affected by aging, smoking, lifestyle, and variants in over 30 genes. Although some genetic associations have been confirmed and validated, individual genes or polygenic risk markers of clinical value have not been established. The genetic architectures of all these complex retinal diseases that involve sequence variant quantitative trait loci have not been fully delineated. Recently artificial intelligence is making an impact in the collection and advanced analysis of genetic, investigative, and lifestyle data for the establishment of predictive factors for the risk of disease onset, progression, and prognosis. This will contribute to individualized precision medicine for the management of complex retinal diseases.

Molecular Genetic Mechanisms in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is among the leading causes of irreversible blindness worldwide. In addition to environmental risk factors, such as tobacco use and diet, genetic background has long been established as a major risk factor for the development of AMD. However, our ability to predict disease risk and personalize treatment remains limited by our nascent understanding of the molecular mechanisms underlying AMD pathogenesis. Research into the molecular genetics of AMD over the past two decades has uncovered 52 independent gene variants and 34 independent loci that are implicated in the development of AMD, accounting for over half of the genetic risk. This research has helped delineate at least five major pathways that may be disrupted in the pathogenesis of AMD: the complement system, extracellular matrix remodeling, lipid metabolism, angiogenesis, and oxidative stress response. This review surveys our current understanding of each of these disease mechanisms, in turn, along with their associated pathogenic gene variants. Continued research into the molecular genetics of AMD holds great promise for the development of precision-targeted, personalized therapies that bring us closer to a cure for this debilitating disease.

A Novel Full-Length Recombinant Human Complement Factor H (CFH; GEM103) for the Treatment of Age-Related Macular Degeneration Shows Similar In Vitro Functional Activity to Native CFH

PURPOSE

GEM103 is a recombinantly produced full-length version of the human complement factor H (CFH) under clinical investigation for treatment of age-related macular degeneration (AMD) in individuals carrying an AMD risk-associated genetic variant of CFH. This study aimed to investigate the complement pathway-related functions of GEM103 in comparison with those of native human CFH.

METHODS

Key biological activities of GEM103 and human serum-derived CFH (sdCFH) were compared using four independent functional assays. Assays of C3b binding and C3 convertase decay-accelerating activity (DAA) were performed by surface plasmon resonance (SPR). Cofactor activity (CA) was measured using 8-anilinonaphthalene-1-sulfonic acid as a fluorescent probe of C3b integrity. The abilities of GEM103 and sdCFH to protect sheep erythrocytes from hemolysis by CFH-depleted normal human serum were assessed colorimetrically.

RESULTS

In multiple SPR-based assays of C3b binding and DAA, the performance of GEM103 was consistently comparable to that of sdCFH across a range of matching concentrations. The EC50 ± SD in the fluorescence-based fluid-phase CA assay was 0.21 ± 0.06 µM for GEM103 compared to 0.20 ± 0.09 µM for sdCFH. In hemolysis assays, the EC50 value of 0.33 ± 0.16 µM for GEM103 versus 0.46 ± 0.06 µM for sdCFH were not significantly different (p = 0.81).

CONCLUSIONS

GEM103, a recombinant CFH developed by Gemini Therapeutics, shows activity profiles comparable to sdCFH in all complement-related assays employed in this study, suggesting that GEM103 is equivalent to the native glycoprotein in terms of its in vitro functional activity. These results support further study of GEM103 as a potential therapy for AMD.

Complement Genetics for the Practicing Allergist Immunologist: Focus on Complement Deficiencies

Complement deficiencies have been considered to be rare for many decades, but this assumption is changing year by year. Recognition of these conditions significantly increases thanks to the availability of different testing approaches and due to clinical awareness. Furthermore, sequencing technologies (including Sanger sequencing, targeted gene panels, and whole exome/genome sequencing) may facilitate the identification of the underlying disease-causing genetic background. On the other hand, functional characterization of the identified possibly pathogenic variations and performing family studies, as illustrated by some of our cases, remain similarly important to establish a precise clinical diagnosis facilitating the most appropriate management. Here, we present 4 illustrative cases with complement deficiencies of diverse etiologies and also provide an educative, step-by-step description on how to identify the underlying cause of complement deficiency based on the results of complement laboratory testing.

Functional analysis of rare genetic variants in complement factor I in advanced age-related macular degeneration

Factor I (FI) is a serine protease inhibitor of the complement system. Heterozygous rare genetic variants in complement factor I (CFI) are associated with advanced age-related macular degeneration (AMD). The clinical impact of these variants is unknown since a majority have not been functionally characterized and are classified as 'variants of uncertain significance' (VUS). This study assessed the functional significance of VUS in CFI. Our previous cross-sectional study using a serum-based assay demonstrated that CFI variants in advanced AMD can be categorized into three types. Type 1 variants cause a quantitative deficiency of FI. Type 2 variants demonstrate a qualitative deficiency. However, Type 3 variants consist of VUS that are less dysfunctional than Types 1 and 2 but are not as biologically active as wild type (WT). In this study, we employed site-directed mutagenesis followed by expression of the recombinant variant and a comprehensive set of functional assays to characterize nine Type 3 variants that were identified in 37 individuals. Our studies establish that the expression of the recombinant protein compared with WT is reduced for R202I, Q217H, S221Y and G263V. Further, G362A and N536K, albeit expressed normally, have significantly less cofactor activity. These results led to re-categorization of CFI variants R202I, Q217H, S221Y and G263V as Type 1 variants and to reclassification of N536K and G362A as Type 2. The variants K441R, Q462H and I492L showed no functional defect and remained as Type 3. This study highlights the utility of an in-depth biochemical analysis in defining the pathologic and clinical implications of complement variants underlying AMD.

Genetic Risk in Families with Age-Related Macular Degeneration

Purpose

To determine the contribution of common and rare genetic risk variants in families with age-related macular degeneration (AMD).

Design

Case-control study.

Participants

A family cohort (355 affected and 342 unaffected family members from 144 families with AMD) and an unrelated case-control cohort (1078 patients, 952 controls), recruited from the European Genetic Database.

Methods

Genetic data of both cohorts were filtered for carriership of rare genetic variants in the coding and splice-site regions of the complement factor H (CFH) and complement factor I (CFI) genes, and 52 AMD-associated variants were extracted for calculation of genetic risk scores (GRS). To compare GRSs between familial and nonfamilial rare CFH and CFI variant carriers and noncarriers and between AMD disease stages, we performed a 2-way analysis of variance, with Bonferroni correction for multiple testing. Within families with AMD carrying rare CFH and CFI variants, we analyzed segregation patterns by calculating the proportion of affected among carriers.

Main Outcome Measures

GRSs and segregation of rare CFH and CFI variants.

Results

We observed higher GRSs in familial versus nonfamilial individuals without rare CFH and CFI variants: mean GRS, 1.76 (standard error [SE], 0.08) versus 0.83 (SE, 0.03; P < 0.001). In 51 of 144 families (35.4%), rare CFH and CFI variants were identified. Within the AMD family cohort, carriers of rare CFH and CFI variants showed lower GRSs compared with noncarriers (mean GRS, 1.05 [SE, 0.23] vs. 1.76 [SE, 0.08]; P = 0.02). The proportion of affected family members with a high GRS was 57.3% (176/307). Of the affected family members with a low or intermediate GRS, 40.0% carried rare CFH or CFI variants. Among carriers of 11 rare CFH or CFI variants, the proportion affected by AMD was more than 75%.

Conclusions

Genetic risk in families with AMD often is attributed to high GRSs based on common variants. However, in part of the families with a low or intermediate GRS, rare CFH and CFI variants contributed to disease development. We recommend computing GRSs and sequencing the CFH and CFI genes in families with AMD, in particular in the light of ongoing gene-specific clinical trials.

Evaluating the Occurrence of Rare Variants in the Complement Factor H Gene in Patients With Early-Onset Drusen Maculopathy

Question

What are the genotypic and phenotypic characteristics of patients with early-onset drusen maculopathy?

Findings

In this case-control study, patients with early-onset drusen maculopathy were frequently carriers of rare genetic variants in the complement factor H gene and were characterized by the presence of a large macular drusen area and lower genetic risk scores compared with patients with age-related macular degeneration.

Meaning

Sequencing of the complement factor H gene is important in considering future treatments targeting the complement system in patients with early-onset drusen maculopathy. Furthermore, the presence of a large macular drusen area supports the severe phenotype in these patients, who may be at high risk of developing geographic atrophy or choroidal neovascularization.

Importance

Early-onset drusen maculopathy (EODM) is a severe disease and can lead to advanced macular degeneration early in life; however, genetic and phenotypic characteristics of individuals with EODM are not well studied.

Objective

To identify genotypic and phenotypic characteristics of individuals with EODM.

Design, Setting, and Participants

This case-control study collected data from the European Genetic Database from September 2004 to October 2019. A total of 89 patients with EODM diagnosed at 55 years or younger and 91 patients with age-related macular degeneration (AMD) diagnosed at 65 years or older were included.

Exposures

Coding regions of CFH, CFI, C3, C9, CFB, ABCA4, PRPH2, TIMP3, and CTNNA1 genes were sequenced, genetic risk scores (GRS) were calculated based on 52 AMD-associated variants, and phenotypic characteristics on color fundus photographs were analyzed comparing patients with EODM and AMD.

Main Outcomes and Measures

GRS, frequency of rare genetic complement variants, and phenotypic characteristics.

Results

This case-control study included 89 patients with EODM (mean [SD] age, 51.8 [8.7] years; 58 [65.2%] were female) and 91 patients with AMD (mean [SD] age, 77.6 [6.1] years; 45 [49.5%] female). At a mean (SD) age of 56.4 (7.3) years, 40 of 89 patients with EODM (44.9%) were affected by geographic atrophy or choroidal neovascularization. A lower GRS was observed in patients with EODM compared with patients with AMD (1.03 vs 1.60; P = .002), and 27 of 89 patients with EODM (30.3%) carried rare variants in the CFH gene compared with 7 of 91 patients with AMD (7.7%). Carriership of a rare CFH variant was associated with EODM (odds ratio, 7.2; 95% CI, 2.7-19.6; P < .001). A large macular drusen area (more than 50% covered with drusen) was observed in patients with EODM (24 of 162 eyes [14.8%]) compared with patients with AMD (9 of 164 eyes [5.5%]) (odds ratio, 4.57; 95% CI, 1.5-14.1; P = .008).

Conclusions and Relevance

A large proportion of patients with EODM in this study carried rare CFH variants, with most of the identified CFH variants clustered in the first 7 complement control protein domains affecting factor H and factor H–like 1. Because EODM frequently leads to advanced macular degeneration at an early age and can result in many years of vision loss, this study supports targeting the complement system and sequencing the CFH gene in patients with EODM to improve genetic counseling and future treatments for AMD.

Family-based exome sequencing identifies rare coding variants in age-related macular degeneration

Genome-wide association studies (GWAS) have identified 52 independent variants at 34 genetic loci that are associated with age-related macular degeneration (AMD), the most common cause of incurable vision loss in the elderly worldwide. However, causal genes at the majority of these loci remain unknown. In this study, we performed whole exome sequencing of 264 individuals from 63 multiplex families with AMD and analyzed the data for rare protein-altering variants in candidate target genes at AMD-associated loci. Rare coding variants were identified in the CFH, PUS7, RXFP2, PHF12 and TACC2 genes in three or more families. In addition, we detected rare coding variants in the C9, SPEF2 and BCAR1 genes, which were previously suggested as likely causative genes at respective AMD susceptibility loci. Identification of rare variants in the CFH and C9 genes in our study validated previous reports of rare variants in complement pathway genes in AMD. We then extended our exome-wide analysis and identified rare protein-altering variants in 13 genes outside the AMD-GWAS loci in three or more families. Two of these genes, SCN10A and KIR2DL4, are of interest because variants in these genes also showed association with AMD in case-control cohorts, albeit not at the level of genome-wide significance. Our study presents the first large-scale, exome-wide analysis of rare variants in AMD. Further independent replications and molecular investigation of candidate target genes, reported here, would assist in gaining novel insights into mechanisms underlying AMD pathogenesis.

Beyond factor H: The impact of genetic-risk variants for age-related macular degeneration on circulating factor-H-like 1 and factor-H-related protein concentrations

Age-related macular degeneration (AMD) is a leading cause of vision loss; there is strong genetic susceptibility at the complement factor H (CFH) locus. This locus encodes a series of complement regulators: factor H (FH), a splice variant factor-H-like 1 (FHL-1), and five factor-H-related proteins (FHR-1 to FHR-5), all involved in the regulation of complement factor C3b turnover. Little is known about how AMD-associated variants at this locus might influence FHL-1 and FHR protein concentrations. We have used a bespoke targeted mass-spectrometry assay to measure the circulating concentrations of all seven complement regulators and demonstrated elevated concentrations in 352 advanced AMD-affected individuals for all FHR proteins (FHR-1, p = 2.4 × 10-10; FHR-2, p = 6.0 × 10-10; FHR-3, p = 1.5 × 10-5; FHR-4, p = 1.3 × 10-3; FHR-5, p = 1.9 × 10-4) and FHL-1 (p = 4.9 × 10-4) when these individuals were compared to 252 controls, whereas no difference was seen for FH (p = 0.94). Genome-wide association analyses in controls revealed genome-wide-significant signals at the CFH locus for all five FHR proteins, and univariate Mendelian-randomization analyses strongly supported the association of FHR-1, FHR-2, FHR-4, and FHR-5 with AMD susceptibility. These findings provide a strong biochemical explanation for how genetically driven alterations in circulating FHR proteins could be major drivers of AMD and highlight the need for research into FHR protein modulation as a viable therapeutic avenue for AMD.

Complement Inhibitors in Age-Related Macular Degeneration: A Potential Therapeutic Option

Age-related macular degeneration (AMD) is a multifactorial disease, which can culminate in irreversible vision loss and blindness in elderly. Nowadays, there is a big gap between dry AMD and wet AMD on treatment. Accounting for nearly 90% of AMD, dry AMD still lacks effective treatment. Numerous genetic and molecular researches have confirmed the significant role of the complement system in the pathogenesis of AMD, leading to a deeper exploration of complement inhibitors in the treatment of AMD. To date, at least 14 different complement inhibitors have been or are being explored in AMD in almost 40 clinical trials. While most complement inhibitors fail to treat AMD successfully, two of them are effective in inhibiting the rate of GA progression in phase II clinical trials, and both of them successfully entered phase III trials. Furthermore, recently emerging complement gene therapy and combination therapy also offer new opportunities to treat AMD in the future. In this review, we aim to introduce genetic and molecular associations between the complement system and AMD, provide the updated progress in complement inhibitors in AMD on clinical trials, and discuss the challenges and prospects of complement therapeutic strategies in AMD.

Prevalence and phenotype associations of complement factor I mutations in geographic atrophy

Rare variants in the complement factor I (CFI) gene, associated with low serum factor I (FI) levels, are strong risk factors for developing the advanced stages of age-related macular degeneration (AMD). No studies have been undertaken on the prevalence of disease-causing CFI mutations in patients with geographic atrophy (GA) secondary to AMD. A multicenter, cross-sectional, noninterventional study was undertaken to identify the prevalence of pathogenic rare CFI gene variants in an unselected cohort of patients with GA and low FI levels. A genotype-phenotype study was performed. Four hundred and sixty-eight patients with GA secondary to AMD were recruited to the study, and 19.4% (n = 91) demonstrated a low serum FI concentration (below 15.6 μg/ml). CFI gene sequencing on these patients resulted in the detection of rare CFI variants in 4.7% (n = 22) of recruited patients. The prevalence of CFI variants in patients with low serum FI levels and GA was 25%. Of the total patients recruited, 3.2% (n = 15) expressed a CFI variant classified as pathogenic or likely pathogenic. The presence of reticular pseudodrusen was detected in all patients with pathogenic CFI gene variants. Patients with pathogenic CFI gene variants and low serum FI levels might be suitable for FI supplementation in therapeutic trials.

Screening of Candidate Pathogenic Genes for Spontaneous Abortion using Whole Exome Sequencing

BACKGROUND

Spontaneous abortion is a common disease in obstetrics and reproduction.

OBJECTIVE

This study aimed to screen candidate pathogenic genes for spontaneous abortion using whole-exome sequencing.

METHODS

Genomic DNA was extracted from abortion tissues of spontaneous abortion patients and sequenced using the Illumina HiSeq2500 high-throughput sequencing platform. Whole exome sequencing was performed to select harmful mutations, including SNP and insertion and deletion sites, associated with spontaneous abortion. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses and gene fusion analyses were performed. MUC3A and PDE4DIP were two novel mutation genes that were screened and verified by PCR in abortion tissues of patients.

RESULTS

A total of 83,633 SNPs and 13,635 Indel mutations were detected, of which 29172 SNPs and 3093 Indels were screened as harmful mutations. The 7 GO-BP, 4 GO-CC, 9 GO-MF progress, and 3 KEGG pathways were enriched in GO and KEGG pathway analyses. A total of 746 gene fusion mutations were obtained, involving 492 genes. MUC3A and PDE4DIP were used for PCR verification because of their high number of mutation sites in all samples.

CONCLUSION

There are extensive SNPs and Indel mutations in the genome of spontaneous abortion tissues, and the effect of these gene mutations on spontaneous abortion needs further experimental verification.

The rare C9 P167S risk variant for age-related macular degeneration increases polymerization of the terminal component of the complement cascade

Age-related macular degeneration (AMD) is a complex neurodegenerative eye disease with behavioral and genetic etiology and is the leading cause of irreversible vision loss among elderly Caucasians. Functionally significant genetic variants in the alternative pathway of complement have been strongly linked to disease. More recently, a rare variant in the terminal pathway of complement has been associated with increased risk, Complement component 9 (C9) P167S. To assess the functional consequence of this variant, C9 levels were measured in two independent cohorts of AMD patients. In both cohorts, it was demonstrated that the P167S variant was associated with low C9 plasma levels. Further analysis showed that patients with advanced AMD had elevated sC5b-9 compared to those with non-advanced AMD, although this was not associated with the P167S polymorphism. Electron microscopy of membrane attack complexes (MACs) generated using recombinantly produced wild type or P167S C9 demonstrated identical MAC ring structures. In functional assays, the P167S variant displayed a higher propensity to polymerize and a small increase in its ability to induce hemolysis of sheep erythrocytes when added to C9-depleted serum. The demonstration that this C9 P167S AMD risk polymorphism displays increased polymerization and functional activity provides a rationale for the gene therapy trials of sCD59 to inhibit the terminal pathway of complement in AMD that are underway.

Implications of genetic variation in the complement system in age-related macular degeneration

Age-related macular degeneration (AMD) is the main cause of vision loss among the elderly in the Western world. While AMD is a multifactorial disease, the complement system was identified as one of the main pathways contributing to disease risk. The strong link between the complement system and AMD was demonstrated by genetic associations, and by elevated complement activation in local eye tissue and in the systemic circulation of AMD patients. Several complement inhibitors have been and are being explored in clinical trials, but thus far with limited success, leaving the majority of AMD patients without treatment options to date. This indicates that there is still a gap of knowledge regarding the functional implications of the complement system in AMD pathogenesis and how to bring these towards clinical translation. Many different experimental set-ups and disease models have been used to study complement activation in vivo and in vitro, and recently emerging patient-derived induced pluripotent stem cells and genome-editing techniques open new opportunities to study AMD disease mechanisms and test new therapeutic strategies in the future. In this review we provide an extensive overview of methods employed to understand the molecular processes of complement activation in AMD pathogenesis. We discuss the findings, advantages and challenges of each approach and conclude with an outlook on how recent, exciting developments can fill in current knowledge gaps and can aid in the development of effective complement-targeting therapeutic strategies in AMD.

Functional Characterization of Rare Genetic Variants in the N-Terminus of Complement Factor H in aHUS, C3G, and AMD

Membranoproliferative glomerulonephritis (MPGN), C3 glomerulopathy (C3G), atypical haemolytic uraemic syndrome (aHUS) and age-related macular degeneration (AMD) have all been strongly linked with dysfunction of the alternative pathway (AP) of complement. A significant proportion of individuals with MPGN, C3G, aHUS and AMD carry rare genetic variants in the CFH gene that cause functional or quantitative deficiencies in the factor H (FH) protein, an important regulator of the AP. In silico analysis of the deleteriousness of rare genetic variants in CFH is not reliable and careful biochemical assessment remains the gold standard. Six N-terminal variants of uncertain significance in CFH were identified in patients with these diseases of the AP and selected for analysis. The variants were produced in Pichia Pastoris in the setting of FH CCPs 1-4, purified by nickel affinity chromatography and size exclusion and characterized by surface plasmon resonance and haemolytic assays as well as by cofactor assays in the fluid phase. A single variant, Q81P demonstrated a profound loss of binding to C3b with consequent loss of cofactor and decay accelerating activity. A further 2 variants, G69E and D130N, demonstrated only subtle defects which could conceivably over time lead to disease progression of more chronic AP diseases such as C3G and AMD. In the variants S159N, A161S, and M162V any functional defect was below the capacity of the experimental assays to reliably detect. This study further underlines the importance of careful biochemical assessment when assigning functional consequences to rare genetic variants that may alter clinical decisions for patients.

Immunological Aspects of Age-Related Macular Degeneration

Increasing evidence over the past two decades points to a pivotal role for immune mechanisms in age-related macular degeneration (AMD) pathobiology. In this chapter, we will explore immunological aspects of AMD, with a specific focus on how immune mechanisms modulate clinical phenotypes of disease and severity and how components of the immune system may serve as triggers for disease progression in both dry and neovascular AMD. We will briefly review the biology of the immune system, defining the role of immune mechanisms in chronic degenerative disease and differentiating from immune responses to acute injury or infection. We will explore current understanding of the roles of innate immunity (especially macrophages), antigen-specific immunity (T cells, B cells, and autoimmunity), immune amplifications systems, especially complement activity and the NLRP3 inflammasome, in the pathogenesis of both dry and neovascular AMD, reviewing data from pathology, experimental animal models, and clinical studies of AMD patients. We will also assess how interactions between the immune system and infectious pathogens could potentially modulate AMD pathobiology via alterations in in immune effector mechanisms. We will conclude by reviewing the paradigm of "response to injury," which provides a means to integrate various immunologic mechanisms along with nonimmune mechanisms of tissue injury and repair as a model to understand the pathobiology of AMD.

Revisiting the role of factor H in age-related macular degeneration: Insights from complement-mediated renal disease and rare genetic variants

Ophthalmologists are long familiar with the eye showing signs of systemic disease, but the association between age-related macular degeneration and abnormal complement activation, common to several renal disorders, has only recently been elucidated. Although complement activation products were identified in drusen almost three decades ago, it was not until the early 21st century that a single-nucleotide polymorphism in the complement factor H gene was identified as a major heritable determinant of age-related macular degeneration, galvanizing global efforts to unravel the pathogenesis of this common disease. Advances in proteomic analyses and familial aggregation studies have revealed distinctive clinical phenotypes segregated by the functional effects of common and rare genetic variants on the mature protein and its splice variant, factor H-like protein 1. The predominance of loss-of-function, N-terminal mutations implicate age-related macular degeneration as a disease of general complement dysregulation, offering several therapeutic avenues for its modulation. Here, we explore the molecular impact of these mutations/polymorphisms on the ability of variant factor H/factor H-like protein 1 to localize to polyanions, pentraxins, proinflammatory triggers, and cell surfaces across ocular and renal tissues and exert its multimodal regulatory functions and their clinical implications. Finally, we critically evaluate key therapeutic and diagnostic efforts in this rapidly evolving field.

Functional Analysis of Rare Genetic Variants in Complement Factor I (CFI) using a Serum-Based Assay in Advanced Age-related Macular Degeneration

Purpose

Factor I (FI) is a serine protease regulator of the complement system. Genetic variants in CFI are associated with advanced age-related macular degeneration (AAMD). However, the clinical and functional impact of these variants is unknown. This study assessed the functional significance of rare CFI variants using a serum-based assay.

Methods

Carriers of rare variants with (n = 78) and without AAMD (n = 28), and noncarriers with (n = 49) and without AMD (n = 44) were evaluated. Function of FI was determined by measuring the proteolytic cleavage of C3b to iC3b, using the cofactor protein, Factor H.

Results

CFI variants were categorized into three groups based on antigenic and functional assessments. Type 1 variants (n = 18) in 35 patients with AAMD demonstrated low serum FI levels and a corresponding decrease in FI function. Type 2 variants (n = 6) in 7 individuals demonstrated normal serum FI antigenic levels but reduced degradation of C3b to iC3b. Type 3 variants (n = 15) in 64 individuals demonstrated normal antigenic levels and degradation of C3b to iC3b. However, iC3b generation was low when measured per unit of FI. Thus most rare CFI variants demonstrate either low antigenic levels (type 1) or normal levels but reduced function (types 2 or 3).

Conclusions

Results provide for the first time a comprehensive functional assessment in serum of CFI rare genetic variants and further establish FI's key role in the pathogenesis of AAMD.

Translational Relevance

Stratifying patients in the clinic with a rare CFI variant will facilitate screening and targeting patients most likely to benefit from complement therapies.

Development of a Genotype Assay for Age-Related Macular Degeneration: The EYE-RISK Consortium

PURPOSE

To develop a genotype assay to assess associations with common and rare age-related macular degeneration (AMD) risk variants, to calculate an overall genetic risk score (GRS), and to identify potential misdiagnoses with inherited macular dystrophies that mimic AMD.

DESIGN

Case-control study.

PARTICIPANTS

Individuals (n = 4740) from 5 European cohorts.

METHODS

We designed single-molecule molecular inversion probes for target selection and used next generation sequencing to sequence 87 single nucleotide polymorphisms (SNPs), coding and splice-site regions of 10 AMD-(related) genes (ARMS2, C3, C9, CD46, CFB, CFH, CFI, HTRA1, TIMP3, and SLC16A8), and 3 genes that cause inherited macular dystrophies (ABCA4, CTNNA1, and PRPH2). Genetic risk scores for common AMD risk variants were calculated based on effect size and genotype of 52 AMD-associated variants. Frequency of rare variants was compared between late AMD patients and control individuals with logistic regression analysis.

MAIN OUTCOME MEASURES

Genetic risk score, association of genetic variants with AMD, and genotype-phenotype correlations.

RESULTS

We observed high concordance rates between our platform and other genotyping platforms for the 69 successfully genotyped SNPs (>96%) and for the rare variants (>99%). We observed a higher GRS for patients with late AMD compared with patients with early/intermediate AMD (P < 0.001) and individuals without AMD (P < 0.001). A higher proportion of pathogenic variants in the CFH (odds ratio [OR] = 2.88; P = 0.006), CFI (OR = 4.45; P = 0.005), and C3 (OR = 6.56; P = 0.0003) genes was observed in late AMD patients compared with control individuals. In 9 patients, we identified pathogenic variants in the PRPH2, ABCA4, and CTNNA1 genes, which allowed reclassification of these patients as having inherited macular dystrophy.

CONCLUSIONS

This study reports a genotype assay for common and rare AMD genetic variants, which can identify individuals at intermediate to high genetic risk of late AMD and enables differential diagnosis of AMD-mimicking dystrophies. Our study supports sequencing of CFH, CFI, and C3 genes because they harbor rare high-risk variants. Carriers of these variants could be amendable for new treatments for AMD that currently are under development.

Exome sequencing for diagnosis of congenital hemolytic anemia

Background

Congenital hemolytic anemia constitutes a heterogeneous group of rare genetic disorders of red blood cells. Diagnosis is based on clinical data, family history and phenotypic testing, genetic analyses being usually performed as a late step. In this study, we explored 40 patients with congenital hemolytic anemia by whole exome sequencing: 20 patients with hereditary spherocytosis and 20 patients with unexplained hemolysis.

Results

A probable genetic cause of disease was identified in 82.5% of the patients (33/40): 100% of those with suspected hereditary spherocytosis (20/20) and 65% of those with unexplained hemolysis (13/20). We found that several patients carried genetic variations in more than one gene (3/20 in the hereditary spherocytosis group, 6/13 fully elucidated patients in the unexplained hemolysis group), giving a more accurate picture of the genetic complexity of congenital hemolytic anemia. In addition, whole exome sequencing allowed us to identify genetic variants in non-congenital hemolytic anemia genes that explained part of the phenotype in 3 patients.

Conclusion

The rapid development of next generation sequencing has rendered the genetic study of these diseases much easier and cheaper. Whole exome sequencing in congenital hemolytic anemia could provide a more precise and quicker diagnosis, improve patients’ healthcare and probably has to be democratized notably for complex cases.

Increased circulating levels of Factor H-Related Protein 4 are strongly associated with age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness. Genetic variants at the chromosome 1q31.3 encompassing the complement factor H (CFH, FH) and CFH related genes (CFHR1-5) are major determinants of AMD susceptibility, but their molecular consequences remain unclear. Here we demonstrate that FHR-4 plays a prominent role in AMD pathogenesis. We show that systemic FHR-4 levels are elevated in AMD (P-value = 7.1 × 10-6), whereas no difference is seen for FH. Furthermore, FHR-4 accumulates in the choriocapillaris, Bruch's membrane and drusen, and can compete with FH/FHL-1 for C3b binding, preventing FI-mediated C3b cleavage. Critically, the protective allele of the strongest AMD-associated CFH locus variant rs10922109 has the highest association with reduced FHR-4 levels (P-value = 2.2 × 10-56), independently of the AMD-protective CFHR1-3 deletion, and even in those individuals that carry the high-risk allele of rs1061170 (Y402H). Our findings identify FHR-4 as a key molecular player contributing to complement dysregulation in AMD.

Choroidal Neovascularization: Mechanisms of Endothelial Dysfunction

Many conditions affecting the heart, brain, and even the eyes have their origins in blood vessel pathology, underscoring the role of vascular regulation. In age-related macular degeneration (AMD), there is excessive growth of abnormal blood vessels in the eye (choroidal neovascularization), eventually leading to vision loss due to detachment of retinal pigmented epithelium. As the advanced stage of this disease involves loss of retinal pigmented epithelium, much less attention has been given to early vascular events such as endothelial dysfunction. Although current gold standard therapy using inhibitors of vascular endothelial growth factor (VEGF) have achieved initial successes, some drawbacks include the lack of long-term restoration of visual acuity, as well as a subset of the patients being refractory to existing treatment, alluding us and others to hypothesize upon VEGF-independent mechanisms. Against this backdrop, we present here a nonexhaustive review on the vascular underpinnings of AMD, implications with genetic and systemic factors, experimental models for studying choroidal neovascularization, and interestingly, on both endothelial-centric pathways and noncell autonomous mechanisms. We hope to shed light on future research directions in improving vascular function in ocular disorders.

Rare Genetic Variants in Jewish Patients Suffering from Age-Related Macular Degeneration

Purpose: To identify rare genetic variants in early age-related macular degeneration (AMD) utilizing whole-exome sequencing (WES). Methods: Eight non-related early-AMD families of different Jewish ethnicities were ascertained. Initial mutation screening (phase-1) included common complement factor-H (CFH) p.Y402H; and age related maculopathy susceptibility 2 (ARMS2) p.A69S; and rare variants complement factor-I (CFI) p.V412M; and hemicentin1 (HMCN1) c.4163delC identified previously in our population. Four families, whose initial screening for the aforementioned variants was negative, underwent WES (phase-2). Bioinformatics filtering was based on functionality (from a panel of 234 genes with proven or presumed association to AMD); predicted severity; and frequency (rare variants with minor allele frequency <1%). When applicable, further screening for specific rare variants was carried out on additional cases of similar ethnicities and phenotypes (phase-3). Results: Phase-1 identified three families carrying CFI p.V412M mutation. WES analysis detected probable disease-related variants in three out of the remaining families. These included: a family with a variant in PLEKHA1 gene p.S177N; a family with previously reported variant p.R1210C in CFH gene; and two families with the C3 p.R735W variant. Conclusions: Rare, high-penetrance variants have a profound contribution to early-AMD pathogenesis. Utilization of WES in genetic research of multifactorial diseases as AMD, allows a thorough comprehensive analysis with the identification of previously unreported rare variants.

Association Between Perifoveal Drusen Burden Determined by OCT and Genetic Risk in Early and Intermediate Age-Related Macular Degeneration

Purpose

The purpose of this study was to determine associations between macular drusen parameters derived from an automatic optical coherence tomography (OCT) algorithm, nonadvanced age-related macular degeneration (AMD) stage, and genetic variants.

Methods

Eyes classified as early or intermediate AMD with OCT imaging and genetic data were selected (n = 239 eyes). Drusen area and volume measurements were estimated using the Zeiss Cirrus advanced retinal pigment epithelium analysis algorithm in a perifoveal zone centered on the fovea. Associations between drusen measurements and common genetic variants in the complement and high-density lipoprotein (HDL) lipid pathways and the ARMS2/HTRA1 variant were calculated using generalized estimating equations and linear mixed models adjusting for age, sex, smoking, body mass index, and education.

Results

Drusen area ≥ the median was independently associated with a higher number of risk alleles for CFH risk score and risk variants in C3 and ARMS2/HTRA1 compared with eyes with no measurable drusen. Similar results were obtained for drusen volume. When all genes were analyzed in the same model, only CFH score and ARMS2/HTRA1 were associated with drusen measurements. HDL pathway genes were not significantly related to drusen parameters. Nonadvanced AMD stages were associated with OCT-derived drusen area and volume.

Conclusions

Variants in CFH and ARMS2/HTRA1, commonly associated with advanced AMD, were independently associated with an increase in drusen burden determined by OCT in an allele dose dependent manner, in eyes with early and intermediate AMD. Biomarkers such as a quantitative classification of nonadvanced AMD and other OCT-derived subphenotypes could provide earlier anatomic endpoints for clinical trials and facilitate the development of new therapies for AMD.

Anti-Factor H Antibody Reactivity in Young Adults Vaccinated with a Meningococcal Serogroup B Vaccine Containing Factor H Binding Protein

Meningococcal serogroup B (MenB) vaccines contain recombinant factor H binding protein (FHbp), which can complex with complement factor H (CFH) and thereby risk eliciting anti-FH autoantibodies. While anti-FH antibodies can be present in sera of healthy persons, the antibodies are implicated in autoimmune atypical hemolytic uremic syndrome and C3 glomerulopathies. We immunized 120 students with a MenB vaccine (Bexsero). By enzyme-linked immunosorbent assay (ELISA), there were small increases in serum anti-FH levels at 3 weeks postvaccination (geometric mean optical density at 405 nm [OD405], 0.54 versus 0.51 preimmunization, P ≤ 0.003 for each schedule tested). There was a similar small increase in anti-FH antibody levels in a second historical MenB study of 20 adults with stored paired preimmunization and postimmunization sera (P = 0.007) but not in three other studies of 57 adults immunized with other meningococcal vaccines that did not contain recombinant FHbp (P = 0.17, 0.84, and 0.60, respectively). Thus, humans vaccinated with MenB-4C develop small increases in serum anti-FH antibody reactivity. Although not likely to be clinically important, the data indicate a host response to FH. In the prospective MenB study, three subjects (2.5%) developed higher anti-FH titers postimmunization. The elevated titers returned to baseline within 3 to 4 months, and none of the subjects reported adverse events during the follow-up. Although anti-FH antibodies can decrease FH function, the postimmunization sera with high anti-FH antibody levels did not impair serum FH function as measured using a hemolytic assay. Thus, while additional studies are warranted, there is no evidence that the anti-FH antibodies elicited by MenB-4C are likely to cause anti-FH-mediated autoimmune disorders. (This study has been registered at ClinicalTrials.gov under registration no. NCT02583412.)IMPORTANCE Meningococci are bacteria that cause sepsis and meningitis. Meningococcal species are subdivided into serogroups on the basis of different sugar capsules. Vaccines that target serogroup A, C, Y, and W capsules are safe and highly effective. New serogroup B (MenB) vaccines target a bacterial protein that can bind to a blood protein called complement factor H (FH). While serogroup B vaccines appear to be safe and effective, there is a theoretical risk that immunization with a bacterial protein that binds host FH might elicit anti-FH autoantibodies. Autoantibodies to FH have been detected in healthy persons but in rare cases can cause certain autoimmune diseases. We found small and/or transient increases in serum antibody to FH after MenB immunization. While no serious adverse events were reported in the subjects with elevated anti-FH titers, since onset of autoimmune disease is a rare event and may occur months or years after vaccination, additional, larger studies are warranted.

The Challenges and Promise of Complement Therapeutics for Ocular Diseases

Ocular inflammation is a defining feature of sight threating diseases and its dysregulation can catalyze and or propagate ocular neurodegenerative maladies such as age-related macular degeneration (AMD). The complement system, an intrinsic component of the innate immunity, has an integral role in maintaining immune-surveillance and homeostasis in the ocular microenvironment; however, overstimulation can drive ocular inflammatory diseases. The mechanism for complement disease propagation in AMD is not fully understood, although there is accumulating evidence showing that targeted modulation of complement-specific proteins has the potential to become a viable therapeutic approach. To date, a major focus of complement therapeutics has been on targeting the alternative complement system in AMD. Recent studies have outlined potential complement cascade inhibitors that might mitigate AMD disease progression. First-in-class complement inhibitors target the modulation of complement proteins C3, C5, factor B, factor D, and properdin. Herein, we will summarize ocular inflammation in the context of AMD disease progression, current clinical outcomes and complications of complement-mediated therapeutics. Given the need for additional therapeutic approaches for ocular inflammatory diseases, targeted complement modulation has emerged as a leading candidate for eliminating inflammation-driven ocular maladies.

Loss-of-Function Mutations in the CFH Gene Affecting Alternatively Encoded Factor H-like 1 Protein Cause Dominant Early-Onset Macular Drusen

Purpose

To characterize the molecular mechanism underpinning early-onset macular drusen (EOMD), a phenotypically severe subtype of age-related macular degeneration (AMD), in a subgroup of patients.

Design

Multicenter case series, in vitro experimentation, and retrospective analysis of previously reported variants.

Participants

Seven families with apparently autosomal dominant EOMD.

Methods

Patients underwent a comprehensive ophthalmic assessment. Affected individuals from families A, B, and E underwent whole exome sequencing. The probands from families C, D, F, and G underwent Sanger sequencing analysis of the complement factor H (CFH) gene. Mutant recombinant factor H like-1 (FHL-1) proteins were expressed in HEK293 cells to assess the impact on FHL-1 expression and function. Previously reported EOMD-causing variants in CFH were reviewed.

Main Outcome Measures

Detailed clinical phenotypes, genomic findings, in vitro characterization of mutation effect on protein function, and postulation of the pathomechanism underpinning EOMD.

Results

All affected participants demonstrated bilateral drusen. The earliest reported age of onset was 16 years (median, 46 years). Ultra-rare (minor allele frequency [MAF], ≤0.0001) CFH variants were identified as the cause of disease in each family: CFH c.1243del, p.(Ala415ProfsTer39) het; c.350+1G→T het; c.619+1G→A het, c.380G→A, p.(Arg127His) het; c.694C→T p.(Arg232Ter) het (identified in 2 unrelated families in this cohort); and c.1291T→A, p.(Cys431Ser). All mutations affect complement control protein domains 2 through 7, and thus are predicted to impact both FHL-1, the predominant isoform in Bruch’s membrane (BrM) of the macula, and factor H (FH). In vitro analysis of recombinant proteins FHL-1_R127H, FHL-1_A415f/s, and FHL-1_C431S demonstrated that they are not secreted, and thus are loss-of-function proteins. Review of 29 previously reported EOMD-causing mutations found that 75.8% (22/29) impact FHL-1 and FH. In total, 86.2% (25/29) of EOMD-associated variants cause haploinsufficiency of FH or FHL-1.

Conclusions

Early-onset macular drusen is an underrecognized, phenotypically severe subtype of AMD. We propose that haploinsufficiency of FHL-1, the main regulator of the complement pathway in BrM, where drusen develop, is an important mechanism underpinning the development of EOMD in a number of cases. Understanding the molecular basis of EOMD will shed light on AMD pathogenesis given their pathologic similarities.

Exome sequencing in families with chronic central serous chorioretinopathy

BACKGROUND

Central serous chorioretinopathy (CSC) is a chorioretinal disease characterized by fluid accumulation between the neuroretina and retinal pigment epithelium with unknown etiology. Family studies have suggested a heritable component for CSC with an autosomal dominant inheritance pattern. Therefore, exome sequencing was performed on familial cCSC to indentify the genetic components contributing to familial cCSC.

METHODS

Exome sequencing was performed on 72 individuals of 18 families with CSC. In these families, we determined whether rare genetic variants (minor allele frequency < 1%) were segregated with CSC and also performed familial gene-burden analysis.

RESULTS

In total, 11 variants segregated in two out of 18 families. One of these variants, c.4145C>T; p.T1382I (rs61758735) in the PTPRB gene, was also associated with CSC in a large case-control cohort sequenced previously (p = 0.009). Additionally, in 28 genes two or more different heterozygous variants segregated in two or more families, but no gene showed consistent associations in both the family gene-burden results and gene-burden analysis in the case-control cohort.

CONCLUSION

We identified potential candidate genes for familial CSC and managed to exclude Mendelian inheritance of variants in one or a limited number of genes. Instead, familial CSC may be a heterogeneous Mendelian disease caused by variants in many different genes, or alternatively CSC may represent a complex disease to which both environmental factors and genetics contribute.

Validated Prediction Models for Macular Degeneration Progression and Predictors of Visual Acuity Loss Identify High-Risk Individuals

PURPOSE

To determine predictive factors and risk scores for conversion to overall advanced age-related macular degeneration (AMD), geographic atrophy (GA), neovascular disease (NV), and loss of vision, and to validate the model for AMD in an external cohort.

METHODS

Progression to advanced AMD was evaluated using stepwise survival analysis. Risk scores including genetic, demographic, behavioral, and ocular factors were derived for 3 AMD endpoints and were validated and calibrated in a large independent cohort. Vision loss of 15 or more letters was evaluated as a new endpoint in genetic analyses.

RESULTS

Eight common and rare variants in genes CFH, C3, ARMS2, COL8A1, and HSPH1/B3GALTL conferred a significantly higher risk of transition to advanced AMD. Three loci (C2, CFB, RAD51B) were associated with lower rate of progression. A protective effect was suggested for CTRB1 and PELI3. The age-adjusted area under the curve (AUC) for the composite model including 13 loci model was 0.900 over 12 years (0.896 in the validation cohort). Generally, progressors had a higher risk category and nonprogressors had a lower risk category when genetic factors were considered. Furthermore, there was heterogeneity between models for GA and NV. The model was calibrated in the validation cohort. Determinants of visual loss included age, education, body mass index, smoking, and several common and rare genetic variants.

CONCLUSION

Eyes with the same baseline macular grade had a wide range of estimated probability of subsequent progression and visual loss based on the validated risk score. Identifying high-risk individuals at an earlier stage using predictive modeling could lead to improved preventive and therapeutic strategies in the era of precision medicine.

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.

Developments in anti-complement therapy; from disease to clinical trial

The complement system is well known for its role in innate immunity and in maintenance of tissue homeostasis, providing a first line of defence against infection and playing a key role in flagging apoptotic cells and debris for disposal. Unfortunately complement also contributes to pathogenesis of a number of diseases; in some cases driving pathology, and in others amplifying or exacerbating the inflammatory and damaging impact of non-complement disease triggers. The role of complement in pathogenesis of an expanding number of diseases has driven industry and academia alike to develop an impressive arsenal of anti-complement drugs which target different proteins and functions of the complement cascade. Evidence from genetic and biochemical analyses, combined with improved identification of complement biomarkers and supportive data from sophisticated animal models of disease, has driven a drug development landscape in which the indications selected for clinical trial cluster in three 'target' tissues: the kidney, eye and vasculature. While the disease triggers may differ, complement activation and amplification is a common feature in many diseases which affect these three tissues. An abundance of drugs are in clinical development, some show favourable progression whereas others experience significant challenges. However, these hurdles in themselves drive an ever-evolving portfolio of 'next-generation' drugs with improved pharmacokinetic and pharmacodynamics properties. In this review we discuss the indications which are in the drug development 'spotlight' and review the relevant indication validation criteria. We present current progress in clinical trials, highlighting successes and difficulties, and look forward to approval of a wide selection of drugs for use in man which give clinicians choice in mechanistic target, modality and route of delivery.

Genotype-phenotype correlations of low-frequency variants in the complement system in renal disease and age-related macular degeneration

Genetic alterations in the complement system have been linked to a variety of diseases, including atypical hemolytic uremic syndrome (aHUS), C3 glomerulopathy (C3G), and age‐related macular degeneration (AMD). We performed sequence analysis of the complement genes complement factor H (CFH), complement factor I (CFI), and complement C3 (C3) in 866 aHUS/C3G and 697 AMD patients. In total, we identified 505 low‐frequency alleles, representing 121 unique variants, of which 51 are novel. CFH contained the largest number of unique low‐frequency variants (n = 64; 53%), followed by C3 (n = 32; 26%) and CFI (n = 25; 21%). A substantial number of variants were found in both patients groups (n = 48; 40%), while 41 (34%) variants were found only in aHUS/C3G and 32 (26%) variants were AMD specific. Genotype‐phenotype correlations between the disease groups identified a higher frequency of protein altering alleles in short consensus repeat 20 (SCR20) of factor H (FH), and in the serine protease domain of factor I (FI) in aHUS/C3G patients. In AMD, a higher frequency of protein‐altering alleles was observed in SCR3, SCR5, and SCR7 of FH, the SRCR domain of FI, and in the MG3 domain of C3. In conclusion, we observed a substantial overlap of variants between aHUS/C3G and AMD; however, there is a distinct clustering of variants within specific domains.

Common and rare genetic variants of complement components in human disease

Genetic variability in the complement system and its association with disease has been known for more than 50 years, but only during the last decade have we begun to understand how this complement genetic variability contributes to the development of diseases. A number of reports have described important genotype-phenotype correlations that associate particular diseases with genetic variants altering specific aspects of the activation and regulation of the complement system. The detailed functional characterization of some of these genetic variants provided key insights into the pathogenic mechanisms underlying these pathologies, which is facilitating the design of specific anti-complement therapies. Importantly, these analyses have sometimes revealed unknown features of the complement proteins. As a whole, these advances have delineated the functional implications of genetic variability in the complement system, which supports the implementation of a precision medicine approach based on the complement genetic makeup of the patients. Here we provide an overview of rare complement variants and common polymorphisms associated with disease and discuss what we have learned from them.

Genetics and genetic testing for age-related macular degeneration

Considerable advances have been made in our understanding of age-related macular degeneration (AMD) genetics over the past decade. The genetic associations discovered to date are estimated to account for approximately half of AMD heritability, and functional studies of these variants have revealed new insights into disease pathogenesis, leading to the development of potential novel therapies. There is furthermore growing interest in genetic testing for predicting an individual's risk of AMD and offering personalised preventive or therapeutic treatments. We review the progress made so far in AMD genetics and discuss the possible applications for genetic testing.

Diseases of complement dysregulation-an overview

Atypical hemolytic uremic syndrome (aHUS), C3 glomerulopathy (C3G), and paroxysmal nocturnal hemoglobinuria (PNH) are prototypical disorders of complement dysregulation. Although complement overactivation is common to all, cell surface alternative pathway dysregulation (aHUS), fluid phase alternative pathway dysregulation (C3G), or terminal pathway dysregulation (PNH) predominates resulting in the very different phenotypes seen in these diseases. The mechanism underlying the dysregulation also varies with predominant acquired autoimmune (C3G), somatic mutations (PNH), or inherited germline mutations (aHUS) predisposing to disease. Eculizumab has revolutionized the treatment of PNH and aHUS although has been less successful in C3G. With the next generation of complement therapeutic in late stage development, these archetypal complement diseases will provide the initial targets.

Family studies to find rare high risk variants in migraine

INTRODUCTION

Migraine has long been known as a common complex disease caused by genetic and environmental factors. The pathophysiology and the specific genetic susceptibility are poorly understood. Common variants only explain a small part of the heritability of migraine. It is thought that rare genetic variants with bigger effect size may be involved in the disease. Since migraine has a tendency to cluster in families, a family approach might be the way to find these variants. This is also indicated by identification of migraine-associated loci in classical linkage-analyses in migraine families. A single migraine study using a candidate-gene approach was performed in 2010 identifying a rare mutation in the TRESK potassium channel segregating in a large family with migraine with aura, but this finding has later become questioned. The technologies of next-generation sequencing (NGS) now provides an affordable tool to investigate the genetic variation in the entire exome or genome. The family-based study design using NGS is described in this paper. We also review family studies using NGS that have been successful in finding rare variants in other common complex diseases in order to argue the promising application of a family approach to migraine.

METHOD

PubMed was searched to find studies that looked for rare genetic variants in common complex diseases through a family-based design using NGS, excluding studies looking for de-novo mutations, or using a candidate-gene approach and studies on cancer. All issues from Nature Genetics and PLOS genetics 2014, 2015 and 2016 (UTAI June) were screened for relevant papers. Reference lists from included and other relevant papers were also searched. For the description of the family-based study design using NGS an in-house protocol was used.

RESULTS

Thirty-two successful studies, which covered 16 different common complex diseases, were included in this paper. We also found a single migraine study. Twenty-three studies found one or a few family specific variants (less than five), while other studies found several possible variants. Not all of them were genome wide significant. Four studies performed follow-up analyses in unrelated cases and controls and calculated odds ratios that supported an association between detected variants and risk of disease. Studies of 11 diseases identified rare variants that segregated fully or to a large degree with the disease in the pedigrees.

CONCLUSION

It is possible to find rare high risk variants for common complex diseases through a family-based approach. One study using a family approach and NGS to find rare variants in migraine has already been published but with strong limitations. More studies are under way.

Phenotype Characteristics of Patients With Age-Related Macular Degeneration Carrying a Rare Variant in the Complement Factor H Gene

Importance

Rare variants in the complement factor H (CFH) gene and their association with age-related macular degeneration (AMD) have been described. However, there is limited literature on the phenotypes accompanying these rare variants. Phenotypical characteristics could help ophthalmologists select patients for additional genetic testing.

Objective

To describe the phenotypical characteristics of patients with AMD carrying a rare variant in the CFH gene.

Design, Setting, and Participants

In this cross-sectional study, we searched the genetic database of the department of ophthalmology at the Radboudumc (tertiary ophthalmologic referral center) and the European Genetic Database for patients with AMD with a rare genetic variant in the CFH gene. Patient recruitment took place from March 30, 2006, to February 18, 2013, and data were analyzed from November 30, 2015, to May 8, 2017. Phenotypical features on fundus photographs of both eyes of patients were graded by 2 independent reading center graders masked for carrier status.

Main Outcomes and Measures

Differences in phenotypical characteristics between rare variant carriers and noncarriers were analyzed using univariable generalized estimated equations logistic regression models accounting for intereye correlation.

Results

Analyses included 100 eyes of 51 patients with AMD carrying a CFH variant (mean [SD] age, 66.7 [12.1] years; 64.7% female) and 204 eyes of 102 age-matched noncarriers (mean [SD] age, 67.1 [11.8] years; 54.9% female). Carrying a rare pathogenic CFH variant was associated with larger drusen area (odds ratio range, 6.98 [95% CI, 2.04-23.89] to 18.50 [95% CI, 2.19-155.99]; P = .002), presence of drusen with crystalline appearance (odds ratio, 3.24; 95% CI, 1.24-8.50; P = .02), and drusen nasal to the optic disc (odds ratio range, 4.03 [95% CI, 1.70-9.56] to 7.42 [95% CI, 0.65-84.84]; P = .003).

Conclusions and Relevance

Identification of rare CFH variant carriers may be important for upcoming complement-inhibiting therapies. Patients with an extensive drusen area, drusen with crystalline appearance, and drusen nasal to the optic disc are more likely to have a rare variant in the CFH gene. However, it is not likely that carriers can be discriminated from noncarriers based solely on phenotypical characteristics from color fundus images. Therefore, ophthalmologists should consider genetic testing in patients with these phenotypic characteristics in combination with other patient characteristics, such as early onset, cuticular drusen on fluorescein angiography, and family history of AMD.

THE PATHOPHYSIOLOGY OF GEOGRAPHIC ATROPHY SECONDARY TO AGE-RELATED MACULAR DEGENERATION AND THE COMPLEMENT PATHWAY AS A THERAPEUTIC TARGET

Geographic atrophy is an advanced form of age-related macular degeneration that can significantly impact visual function, but has no approved treatment. This review focuses on the pathophysiology of geographic atrophy, particularly the role of complement cascade dysregulation and emerging therapies targeting the complement cascade.

Purpose:

Geographic atrophy (GA) is an advanced, vision-threatening form of age-related macular degeneration (AMD) affecting approximately five million individuals worldwide. To date, there are no approved therapeutics for GA treatment; however, several are in clinical trials. This review focuses on the pathophysiology of GA, particularly the role of complement cascade dysregulation and emerging therapies targeting the complement cascade.

Methods:

Primary literature search on PubMed for GA, complement cascade in age-related macular degeneration. ClinicalTrials.gov was searched for natural history studies in GA and clinical trials of drugs targeting the complement cascade for GA.

Results:

Cumulative damage to the retina by aging, environmental stress, and other factors triggers inflammation via multiple pathways, including the complement cascade. When regulatory components in these pathways are compromised, as with several GA-linked genetic risk factors in the complement cascade, chronic inflammation can ultimately lead to the retinal cell death characteristic of GA. Complement inhibition has been identified as a key candidate for therapeutic intervention, and drugs targeting the complement pathway are currently in clinical trials.

Conclusion:

The complement cascade is a strategic target for GA therapy. Further research, including on natural history and genetics, is crucial to expand the understanding of GA pathophysiology and identify effective therapeutic targets.

Complete functional characterization of disease-associated genetic variants in the complement factor H gene

Genetic analyses in atypical hemolytic uremic syndrome (aHUS) and C3-glomerulopathy (C3G) patients have provided an excellent understanding of the genetic component of the disease and informed genotype-phenotype correlations supporting an individualized approach to patient management and treatment. In this context, a correct categorization of the disease-associated gene variants is critical to avoid detrimental consequences for patients and their relatives. Here we describe a comprehensive procedure to measure levels and functional activity of complement regulator factor H (FH) encoded by CFH, the commonest genetic factor associated with aHUS and C3G, and present the results of the analysis of 28 uncharacterized, disease-associated, FH variants. Sixteen variants were not expressed in plasma and eight had significantly reduced functional activities that impact on complement regulation. In total, 24 of 28 CFH variants were unambiguously categorized as pathogenic and the nature of the pathogenicity fully documented for each. The data also reinforce the genotype-phenotype correlations that associate specific FH functional alterations with either aHUS or C3G and illustrate important drawbacks of the prediction algorithms dealing with variants located in FH functional regions. We also report that the novel aHUS-associated M823T variant is functionally impaired. This was unexpected and uncovered the important contribution of regions outside the N-terminal and C-terminal functional domains to FH regulatory activities on surfaces. Thus, our work significantly advances knowledge towards a complete functional understanding of the CFH genetic variability and highlights the importance of functional analysis of the disease-associated CFH variants.

Complement factor H in AMD: Bridging genetic associations and pathobiology

Age-Related Macular Degeneration (AMD) is a complex multifactorial disease characterized in its early stages by lipoprotein accumulations in Bruch's Membrane (BrM), seen on fundoscopic exam as drusen, and in its late forms by neovascularization ("wet") or geographic atrophy of the Retinal Pigmented Epithelial (RPE) cell layer ("dry"). Genetic studies have strongly supported a relationship between the alternative complement cascade, in particular the common H402 variant in Complement Factor H (CFH) and development of AMD. However, the functional significance of the CFH Y402H polymorphism remains elusive. In this article, we critically review the literature surrounding the functional significance of this polymorphism. Furthermore, based on our group's studies we propose a model in which CFH H402 affects CFH binding to heparan sulfate proteoglycans leading to accelerated lipoprotein accumulation in BrM and drusen progression. We also review the literature on the role of other complement components in AMD pathobiologies, including C3a, C5a and the membrane attack complex (MAC), and on transgenic mouse models developed to interrogate in vivo the effects of the CFH Y402H polymorphism.

Hemolytic Uremic Syndrome in Pregnancy and Postpartum

BACKGROUND

Pregnancy is associated with various forms of thrombotic microangiopathy, including hemolytic uremic syndrome. A previous small French study suggested that pregnancy-associated hemolytic uremic syndrome was to be included in the spectrum of atypical hemolytic uremic syndrome linked to complement alternative pathway dysregulation.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We sought to retrospectively analyze the presentation, outcome, and frequency of complement alternative pathway gene variants in a larger international (France, United Kingdom, Italy) cohort of patients with pregnancy-associated hemolytic uremic syndrome.

RESULTS

Eighty-seven patients with pregnancy-associated hemolytic uremic syndrome were included. Hemolytic uremic syndrome occurred mainly during the first pregnancy (58%) and in the postpartum period (76%). At diagnosis, 56 (71%) patients required dialysis. Fifty-six (78%) patients underwent plasma exchanges, 21 (41%) received plasma infusions, and four (5%) received eculizumab. During follow-up (mean duration of 7.2 years), 41 (53%) patients reached ESRD, 15 (19%) had CKD, and 18 (28%) patients experienced hemolytic uremic syndrome relapse. Twenty-four patients (27%) received a kidney transplant and a recurrence of hemolytic uremic syndrome occurred in 13 (54%) patients. Variants in complement genes were detected in 49 (56%) patients, mainly in the CFH (30%) and CFI genes (9%).

CONCLUSIONS

Pregnancy-associated hemolytic uremic syndrome and atypical hemolytic uremic syndrome nonrelated to pregnancy have the same severity at onset and during follow-up and the same frequency of complement gene variants.

Investigation of associations of ARMS2, CD14, and TLR4 gene polymorphisms with wet age-related macular degeneration in a Greek population

Background

Age-related macular degeneration (AMD) is a multifactorial degenerative ocular disease that leads to loss of central vision. Functional gene polymorphisms have already been associated with the disease (for example, ARMS2 A69S, rs10490924).

Aim

The goal of our study was to verify the correlation of the aforementioned ARMS2 variation with the disease, to examine, for the first time, the role of the CD14 C260T variation (rs2569190), and to investigate the association of two TLR4 polymorphisms (Asp299Gly or rs4986790 and Thr399Ile or rs4986791) in a Greek population with the wet form of AMD.

Patients and methods

Genomic DNAs were isolated from blood samples of 103 healthy controls and 120 Greek patients with wet AMD who were age- and sex-matched, and all of whom were clinically evaluated. For the genotyping of all selected polymorphisms, polymerase chain reaction–restriction fragment length polymorphism analysis was performed.

Results and conclusions

This study confirmed the association between the ARMS2 variation and AMD, detecting the T risk allele in a significantly higher frequency in the patient group, compared with the control subjects (45% vs 29.13%, P<0.001, odds ratio [OR] 1.99, confidence interval 1.34–2.95). For the CD14 polymorphism, no statistically significant correlation was observed. As for the TLR4 polymorphisms, the percentage of heterozygotes increased from 2.9% to 11.7% in the patient population for Asp299Gly and from 1.9% to 10% for the Thr399Ile polymorphism (ORs 4.40 [P=0.01] and 5.61 [P=0.0088], respectively). Although our ARMS2 and CD14 results provided definite conclusions, the role of innate immunity TLR4 gene awaits further investigation in larger AMD populations with more clinical data collected on past microbial infections.