The Functional Effect of Rare Variants in Complement Genes on C3b Degradation in Patients With Age-Related Macular Degeneration

Abstract

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 μg/mL in Gly119Arg carriers and 16.2 μg/mL in Leu131Arg carriers vs 27.2 and 30.4 μg/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 (R 2 = 0.35 and R 2 = 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 patie...

Omics Biomarkers in Ophthalmology

“…Omics experiments could play a role in determining whether a patient falls into this category. 133 The concept of personalized medicine is already in a more advanced stage in the field of cancer research. For instance, genomic and transcriptomic profiles are being used for prognosis and treatment decisions in breast cancer, and several clinical trials in this field are ongoing.…”

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

“…New genetic variants were detected in CFH , CFI , C3 and C9 , in addition to other genes ( FBN2 and HMCN1 ). Although rare variants segregated with AMD in some of these families (Pras et al, 2015, Ratnapriya et al, 2014, Yu et al, 2014), several variants did not perfectly segregate with the disease, but were enriched in cases compared to control individuals (Geerlings et al, 2016, Hoffman et al, 2014, Saksens et al, 2016). This is in line with the complex etiology of AMD, to which both common and rare genetic variants, and also environmental factors contribute.…”

“…Since WES and WGS are expensive to perform in large cohorts, approaches can be used to enrich for rare variants, for example by analyzing large AMD families. Recent studies in AMD using WES and WGS have successfully identified novel genetic variants in AMD using a case-control cohort (Helgason et al, 2013) or by analyzing multiple affected individuals of large AMD families (Duvvari et al, 2016, Geerlings et al, 2016, Hoffman et al, 2014, Pras et al, 2015, Ratnapriya et al, 2014, Saksens et al, 2016, Yu et al, 2014). New genetic variants were detected in CFH , CFI , C3 and C9 , in addition to other genes ( FBN2 and HMCN1 ).…”

“…Splice site variant CFH c.790 + 1G > A and coding variants CFH Arg53Cys, Asp90Gly, Arg127His, Arg175Pro, Arg175Gln, Cys192Phe, and Ser193Leu were identified by WES of AMD families in which known genetic risk factors could not explain the high burden of disease (Geerlings et al, 2016, Wagner et al, 2016, Yu et al, 2014). Variant CFH Pro503Ala was identified using WES in an Amish family after exclusion of the other main risk variants for AMD, and was significantly associated with AMD in an Amish AMD case-control cohort (Hoffman et al, 2014) (Table 2).…”

“…Additional variants in CFI have been identified in AMD families, including Gly188Ala (van de Ven et al, 2013), Leu131Arg (Geerlings et al, 2016), and Val412Met (Pras et al, 2015). It has been demonstrated that the CFI gene is enriched for rare variants four-fold in AMD cases compared to controls, and that these variants largely reside in the catalytic domain (residing in the serine protease domain) of the protein (Seddon et al, 2013).…”