Maartje J. Geerlings

Rare Genetic Variants Associated With Development of Age-Related Macular Degeneration

IMPORTANCE Rare variants in the complement genes CFH, CFI, C9, and C3 have been found to be highly associated with age-related macular degeneration (AMD); however, the effect on clinical characteristics and familial segregation by these variants is lacking. OBJECTIVES To determine the contribution of rare CFH Arg1210Cys, CFI Gly119Arg, C9 Pro167Ser, and C3 Lys155Gln variants in the development of AMD in 22 multiplex families and to describe clinical differences in carriers vs noncarriers in these families and a large case-control cohort. DESIGN, SETTING, AND PARTICIPANTS This retrospective case-control study included 114 affected and 60 unaffected members of 22 multiplex families with AMD as well as 1589 unrelated patients with AMD and 1386 unrelated control individuals enrolled in the European Genetic Database (EUGENDA). Patients were recruited from March 29, 2006, to April 26, 2013, and data were collected from April 20, 2012, to May 7, 2014. All participants underwent an extensive ophthalmic examination and completed a questionnaire. Venous blood samples were obtained from all participants for genetic analysis, including whole-exome sequencing and measurements of complement activation. Data were analyzed from September 23, 2014, to November 4, 2015. MAIN OUTCOMES AND MEASURES Differences between carriers and noncarriers of rare variants in age at onset of symptoms, the family history of AMD, complement activation levels (C3d:C3 ratio), the presence of reticular pseudodrusen, and AMD phenotype. RESULTS Among the 114 affected and 60 unaffected members of 22 multiplex families with AMD and the 1598 unrelated patients with AMD and 1386 controls in the EUGENDA cohort who underwent analysis, the presence of the CFI Gly119Arg, C9 Pro167Ser, or C3 Lys155Gln variant was confirmed in 18 individuals in 5 families but did not completely segregate with the disease. In the case-control cohort, the 91 affected carriers of these variants were younger at symptom onset (mean [SD] age, 67.4 [8.5] vs 71.3 [8.9] years; P = .01) and more often reported a positive family history (35 of 79 [44.3%] vs 367 of 1201 [30.6%]; P = .008) compared with the 1498 noncarriers. Patients with advanced atrophic AMD carried these rare variants more frequently than patients with neovascular AMD (11 of 93 [11.8%] vs 40 of 835 [4.8%]; P = .04). CONCLUSIONS AND RELEVANCE Previously reported rare variants do not completely segregate within families with AMD. However, patients carrying these rare variants differ clinically from noncarriers by an earlier age at symptom onset, higher prevalence of a positive family history, and AMD phenotype. These results suggest that genetic tests for AMD might be designed to detect common and rare genetic variants, especially in families, because rare variants contribute to the age at onset and progression of the disease.

The complement system in age-related macular degeneration: A review of rare genetic variants and implications for personalized treatment

HighlightsThe complement system plays a central role in age‐related macular degeneration (AMD).Common and rare genetic variants in complement genes have been identified in AMD.Several of the rare variants affect the functioning of the complement system.However, a genetic association with AMD cannot always be proven.Functional assays can help identify patients for complement inhibiting therapies. Abstract Age‐related macular degeneration (AMD) is a progressive retinal disease and the major cause of irreversible vision loss in the elderly. Numerous studies have found both common and rare genetic variants in the complement pathway to play a role in the pathogenesis of AMD. In this review we provide an overview of rare variants identified in AMD patients, and summarize the functional consequences of rare genetic variation in complement genes on the complement system. Finally, we discuss the relevance of this work in light of ongoing clinical trials that study the effectiveness of complement inhibitors against AMD.

The functional effect of rare variants in complement genes on C3b degradation in patients with age-related macular degeneration

Importance In age-related macular degeneration (AMD), rare variants in the complement system have been described, but their functional consequences remain largely unexplored. Objectives To identify new rare variants in complement genes and determine the functional effect of identified variants on complement levels and complement regulation in serum samples from carriers and noncarriers. Design, Setting, and Participants This study evaluated affected (n = 114) and unaffected (n = 60) members of 22 families with AMD and a case-control cohort consisting of 1831 unrelated patients with AMD and 1367 control individuals from the European Genetic Database from March 29, 2006, to April 26, 2013, in Nijmegen, the Netherlands, and Cologne, Germany. Exome sequencing data of families were filtered for rare variants in the complement factor H (CFH), complement factor I (CFI), complement C9 (C9), and complement C3 (C3) genes. The case-control cohort was genotyped with allele-specific assays. Serum samples were obtained from carriers of identified variants (n = 177) and age-matched noncarriers (n = 157). Serum concentrations of factor H (FH), factor I (FI), C9, and C3 were measured, and C3b degradation ability was determined. Main Outcomes and Measures Association of rare variants in the CFH, CFI, C9, and C3 genes with AMD, serum levels of corresponding proteins, and C3b degradation ability of CFH and CFI variant carriers. Results The 1831 unrelated patients with AMD had a mean (SD) age of 75.0 (9.4) years, and 60.5% were female. The 1367 unrelated control participants had a mean (SD) age of 70.4 (7.0), and 58.7% were female. All individuals were of European descent. Rare variants in CFH, CFI, C9, and C3 contributed to an increased risk of developing AMD (odds ratio, 2.04; 95% CI, 1.47-2.82; P < .001). CFI carriers had decreased median FI serum levels (18.2 &mgr;g/mL in Gly119Arg carriers and 16.2 &mgr;g/mL in Leu131Arg carriers vs 27.2 and 30.4 &mgr;g/mL in noncarrier cases and controls, respectively; both P < .001). Elevated C9 levels were observed in Pro167Ser carriers (10.7 µg/mL vs 6.6 and 6.1 µg/mL in noncarrier cases and controls, respectively; P < .001). The median FH serum levels were 299.4 µg/mL for CFH Arg175Gln and 266.3 µg/mL for CFH Ser193Leu carriers vs 302.4 and 283.0 µg/mL for noncarrier cases and controls, respectively. The median C3 serum levels were 943.2 µg/mL for C3 Arg161Trp and 946.7 µg/mL for C3 Lys155Gln carriers vs 874.0 and 946.7 µg/mL for noncarrier cases and controls, respectively. The FH and FI levels correlated with C3b degradation in noncarriers (R2 = 0.35 and R2 = 0.31, respectively; both P < .001). Conclusions and Relevance Reduced serum levels were associated with C3b degradation in carriers of CFI but not CFH variants, suggesting that CFH variants affect functional activity of FH rather than serum levels. Carriers of CFH (Arg175Gln and Ser193Leu) and CFI (Gly119Arg and Leu131Arg) variants have an impaired ability to regulate complement activation and may benefit more from complement-inhibiting therapy than patients with AMD in general.

Whole Exome Sequencing in Patients with the Cuticular Drusen Subtype of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in elderly people worldwide. Cuticular drusen (CD) is a clinical subtype of AMD, which typically displays an earlier age at onset, and has a strong genetic component. Genetic studies support a role for rare sequence variants in CD susceptibility, and rare sequence variants in the CFH gene have been identified in 8.8% of CD cases. To further explore the role of rare variants in CD, we performed whole exome sequencing (WES) in 14 affected members of six families and 12 sporadic cases with CD. We detected rare sequence variants in CFH and FBLN5, which previously were shown to harbor rare variants in patients with CD. In addition, we detected heterozygous rare sequence variants in several genes encoding components of the extracellular matrix (ECM), including FBLN1, FBLN3/EFEMP1, FBLN5, FBLN6/HMCN1, FBN2, and COL15A1. Two rare pathogenic variants were identified in the COL15A1 gene: one in a sporadic case and another was found to segregate in a family with six affected individuals with CD. In addition, two rare pathogenic variants were identified in the FGL1 gene in three unrelated CD cases. These findings suggest that alterations in the ECM and in the coagulation pathway may play a role in the pathogenesis of CD. The identified candidate genes require further analyses in larger cohorts to confirm their role in the CD subtype of AMD. No evidence was found of rare sequence variants in a single gene that segregate with CD in the six families, suggesting that the disease is genetically heterogeneous.

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.

Whole-Exome Sequencing in Age-Related Macular Degeneration Identifies Rare Variants in COL8A1, a Component of Bruch's Membrane

Purpose Genome-wide association studies and targeted sequencing studies of candidate genes have identified common and rare variants that are associated with age-related macular degeneration (AMD). Whole-exome sequencing (WES) studies allow a more comprehensive analysis of rare coding variants across all genes of the genome and will contribute to a better understanding of the underlying disease mechanisms. To date, the number of WES studies in AMD case-control cohorts remains scarce and sample sizes are limited. To scrutinize the role of rare protein-altering variants in AMD cause, we performed the largest WES study in AMD to date in a large European cohort consisting of 1125 AMD patients and 1361 control participants. Design Genome-wide case-control association study of WES data. Participants One thousand one hundred twenty-five AMD patients and 1361 control participants. Methods A single variant association test of WES data was performed to detect variants that are associated individually with AMD. The cumulative effect of multiple rare variants with 1 gene was analyzed using a gene-based CMC burden test. Immunohistochemistry was performed to determine the localization of the Col8a1 protein in mouse eyes. Main Outcome Measures Genetic variants associated with AMD. Results We detected significantly more rare protein-altering variants in the COL8A1 gene in patients (22/2250 alleles [1.0%]) than in control participants (11/2722 alleles [0.4%]; P = 7.07×10–5). The association of rare variants in the COL8A1 gene is independent of the common intergenic variant (rs140647181) near the COL8A1 gene previously associated with AMD. We demonstrated that the Col8a1 protein localizes at Bruch’s membrane. Conclusions This study supported a role for protein-altering variants in the COL8A1 gene in AMD pathogenesis. We demonstrated the presence of Col8a1 in Bruch’s membrane, further supporting the role of COL8A1 variants in AMD pathogenesis. Protein-altering variants in COL8A1 may alter the integrity of Bruch’s membrane, contributing to the accumulation of drusen and the development of AMD.

Genetic screening for macular dystrophies in patients clinically diagnosed with dry age-related macular degeneration

It can be clinically challenging to distinguish dry age‐related macular degeneration (AMD) from AMD‐mimicking dystrophies, and sometimes misdiagnosis occurs. With upcoming therapies for dry AMD it is important to exclude patients with a different retinal disease from clinical trials. In this study we evaluated the occurrence of AMD‐mimicking dystrophies in an AMD cohort. Whole‐exome sequencing (WES) was performed in 218 patients with intermediate AMD or geographic atrophy secondary to AMD and 133 control individuals. WES data was analyzed for rare variants in 19 genes associated with autosomal dominant and recessive macular dystrophies mimicking AMD. In three (1.4%) of 218 cases we identified a pathogenic heterozygous variant (PRPH2 c.424C > T; p.R142W) causal for autosomal dominant central areolar choroidal dystrophy (CACD). Phenotypically, these patients all presented with geographic atrophy. In 12 (5.5%) of 218 cases we identified a heterozygous variant of unknown clinical significance, but predicted to be highly deleterious, in genes previously associated with autosomal dominant macular dystrophies. The distinction between AMD and AMD‐mimicking dystrophies, such as CACD, can be challenging based on fundus examination alone. Genetic screening for genes associated with macular dystrophies, especially PRPH2, can be beneficial to help identify AMD‐mimicking dystrophies.

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.