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CFHR Variations Provide Insights in the Pathogenesis of the Kidney Diseases Atypical Hemolytic Uremic Syndrome and C3 Glomerulopathy

Peter F. Zipfel ,1,2 Thorsten Wiech,3 Emma D. Stea,1 and Christine Skerka 1

1Department of Infection Biology, Leibniz Institute for Natural Product Research and Infection Biology, Jena, Germany; 2Institute of Microbiology, Friedrich-Schiller-University, Jena, Germany; and 3Section of Nephropathology, Institute of Pathology, University Hospital Hamburg-Eppendorf, Hamburg, Germany

ABSTRACT Sequence and copy number variations in the human CFHR– gene cluster regulation on endothelial surfaces and comprising the complement CFHR1, CFHR2, CFHR3, CFHR4, CFHR5, and fluid-phase regulation remains intact. In Factor H are linked to the human kidney diseases atypical hemolytic uremic syn- C3 glomerulopathy, FHR mutants in the drome (aHUS) and C3 glomerulopathy. Distinct genetic and chromosomal alter- context of intact Factor H and FHL1 (the ations, deletions, or duplications generate hybrid or mutant CFHR genes, as well Factor H–like ) affect complement as hybrid CFHR–Factor H genes, and alter the FHR and Factor H plasma repertoire. regulation in the fluid phase and on the A clear association between the genetic modifications and the pathologic outcome glomerular surface, and FHR mutants is emerging: CFHR1, CFHR3,andFactor H gene alterations combined with intact with duplicated interaction segments CFHR2, CFHR4,andCFHR5 genes are reported in atypical hemolytic uremic syn- form large oligomers, which deregulate drome. But alterations in each of the five CFHR genes in the context of an intact complement and compete with Factor H Factor H gene are described in C3 glomerulopathy. These genetic modifications for surface binding. Thus, C3 glomerulop- influence complement function and the interplay of the five FHR with each athy develops due to unique CFHR gene other and with Factor H. Understanding how mutant or hybrid FHR proteins, Factor variations in the context of an intact Factor H::FHR hybrid proteins, and altered Factor H, FHR plasma profiles cause pathology H gene. is of high interest for diagnosis and therapy. Here, we summarize how modifica- tions in the CFHR gene cluster described JASN 31: 241–256, 2020. doi: https://doi.org/10.1681/ASN.2019050515 for aHUS and C3 glomerulopathy cause specific FHR mutants and how they affect the FHR plasma repertoire. Thereby, this Sequence and copy number variations in Factor H on the endothelial surface is review will focus on (1) providing an over- the human CFHR gene cluster are linked altered. In C3 glomerulopathy, the FHR view of complement initiation, with the to the kidney disorders atypical hemo- mutants and a modified FHR plasma two central enzymatic levels and the various lyticuremicsyndrome(aHUS)andC3 repertoire apparently affect local com- effector actions; (2) the characteristic glomerulopathy,1–6 and are further- plement regulation, inducing cell pro- more associated with IgA nephropathy liferation and chronic inflammation. fi (IgAN), with a retinal disease, and with To evaluate how alterations in the ve Published online ahead of print. Publication date – infections.5 8 These copy number varia- CFHR genes and the Factor H gene cause available at www.jasn.org. tions are caused by deletions, duplications, different renal pathologies, we here link Presentaddress:Dr.EmmaD.Stea,Nephrology, and insertions of gene or chromosomal the genetic scenarios, the specificFHR Dialysis and Transplantation Unit, Department of segments and generate CFHR::CFHR, variants expressed in plasma, with the Emergency and Organ Transplantation, University ‘ ’ CFHR::Factor H,andFactor H::CFHR glomerular changes in these kidney dis- Aldo Moro, Bari, Italy. hybrid genes or CFHR genes with dupli- eases. We summarize the role of FHR Correspondence: Prof. Peter F. Zipfel, Department cated elements and result in FHR hybrid proteins as emerging complement mod- of Infection Biology, Leibniz Institute for Natural Products Research and Infection Biology, Beutenbergstr 1 fi fl or mutant proteins and alter the FHR and ulators, ampli ers, and in ammatory 11a, Jena D-07745, Thueringen, Germany. Email: Factor H plasma repertoire. One clear dif- modifiers. In aHUS FHR mutants and in [email protected] ference is emerging: in aHUS, ultimately autoimmune aHUS pathogenic Factor Copyright © 2020 by the American Society of the protective complement action of H–binding autoantibodies alter Factor H Nephrology

JASN 31: 241–256, 2020 ISSN : 1046-6673/3102-241 241 REVIEW www.jasn.org morphologic features of the human AP and the convertase (C2bC4bC3b) of Significance Statement kidney disorders aHUS and C3 glomerul- the LP/CP-pathway use C5 as substrate opathy; (3) giving a brief summary on the and generate C5a and C5b. The human CFHR–Factor H gene cluster organization of the human CFHR–Factor Complement action occurs in the encodes the five FHR proteins that are H gene cluster with the Factor H and the fluid phase and on surfaces and multiple emerging complement and immune mod- fi ulators and the two complement regulators ve CFHR genes and on the structure of regulators control activation and the Factor H and FHL1. Genetic and chromo- the encoded FHR proteins; (4) explaining transition from fluid phase to the surface.9 somal alterations in this cluster are associ- how, in aHUS, CFHR gene variations Both C3 convertases form the inflamma- ated with the human kidney diseases generate Factor H::FHR3, Factor H::FHR1, tory anaphylatoxin C3a and the opsonin atypical hemolytic uremic syndrome and and FHR1::Factor H hybrid proteins and C3b. C3b is handled differently on self and C3 glomerulopathy. Various genetic alter- ations result in the expression of mutant how they alter FHR plasma levels; (5)de- nonself surfaces. C3b deposited on intact and altered FHR proteins, or FHR::Factor H scribing which genetic CFHR changes oc- self surfaces is inactivated by complement and Factor H::FHR hybrid proteins. The cur in C3 glomerulopathy; (6) describing proteases which act together with cofac- modified FHR proteins together with an which FHR hybrid or FHR mutant proteins tors, and inactivated iC3b is further pro- altered FHR and Factor H plasma reper- are expressed in this disease; (7) describing cessed to C3dg and C3d. In addition, C3b toire, which often modify complement action in the fluid phase and cause mor- how altered FHR plasma levels result in C3 when deposited to foreign surfaces ini- phologic alteration in the glomerulus, glomerulopathy; (8) summarizing the new tiates the amplification loop that amplifies provide important views on FHR protein insights into the role of the FHR proteins in C3b deposition. The second enzymatic function in the kidney. IgAN,incomplementcontrolanddisease level with the C5 convertase generates pathology; and (9) providing concluding the potent anaphylatoxin C5a and de- that are causative for the two kidney remarks and an outlook for diagnosis, bio- posits C5b, which initiates the pore- diseases, genetic aHUS and C3 glomerul- marker profiling, and therapy. forming terminal complement complex opathy. The morphologic and cellular al- (TCC) (Figure 1A).13,14 Thus, two enzy- terations, which are caused by deregulated matic steps generate different effector com- complement, are summarized in recent COMPLEMENT: INITIATION, pounds (1) in the form of anaphylatoxins excellent reviews.17,18 The morphologic ENZYMATIC LEVELS, AND C3a and C5a that induce inflammation appearance of aHUS in the glomeruli EFFECTOR PATHWAYS and attract host cells; (2)byopsonization and the preglomerular arterioles can be of target surfaces with C3b; and (3)by characterized as thrombotic microangi- Complement is a central homeotic sys- forming the TCC, which generates a pore tem and defective complement causes and damages the target membrane.15,16 opathy. Best understood is primary many human diseases, in particular the An important challenge is to understand complement-mediated endothelial and kidney diseases aHUS and C3 glomerul- complement regulation and the actions of mesangial cell damage due to dysregulation opathy.9,10 In order to link complement existing regulators and new modulators. of the alternative complement cascade on 19 with CFHR gene variations a brief over- Given that FHR proteins are emerging com- the cell surface. Defective complement view of complement, with the three ac- plement modulators and amplifiers, it is of control on endothelial surfaces results in tivation pathways and with two central interest to define at which specificstepofa cell lysis, followed by thrombus forma- enzymatic checkpoints, is presented pathway and at which checkpoints each tion, loss of mesangial cells, and mesan- (Figure 1A). Activation of the alternative FHR protein acts. The different pathologies giolysis as seen in histology (Figure 1C). pathway occurs spontaneously in the caused by the FHR mutants and hybrids, In the chronic or repair phase, the newly fluid phase and propels on target surfaces; i.e., endothelial damage in aHUS and in formed endothelial cells produce new extra- the lectin and the classic pathways are ini- DEAP-HUS (homozygous CFHR1-CFHR3 cellular matrix, leading to double contours tiated on target surfaces by carbohydrates Deficiency and Autoantibody to Factor H of the glomerular basement membrane and antibodies bound to antigens.9–11 Positive), and inflammatory and prolifera- (GBM) thickening.17,18 In contrast, in C3 Upon initiation, two subsequently acting tive action in C3 glomerulopathy already in- glomerulopathy, chronic complement acti- enzymatic effector systems are formed. dicate different regulatory and modulatory vation in the fluid phase and/or on the sur- The first enzymatic level is mediated by and amplifiers roles of FHR proteins in the face leads to deposition of complement two C3 convertases, the AP (C3bBb) and complement cascade. components in the mesangium and in the the LP/CP (C2bC4b) convertases, which subendothelial space (membranoproli- cleave the same substrate C3 and gener- ferative GN [MPGN] pattern), or within ate C3a and C3b.12 This enzymatic level RENAL HISTOLOGIC CHANGES IN the GBM (intramembranous GN, dense includes a self-amplifying amplification AHUS AND IN C3 deposit disease (DDD) pattern), and some- loop that enhances activation. The sec- GLOMERULOPATHY times also at the outer aspects of the GBM ond enzyme level generates C5 converta- (subepithelial deposits) (Figure 1D).20 ses. Again, two enzymes are generated; Chromosomal changes in the CFHR–Factor Depot formation is followed by mesan- both the convertase (C3bBbC3b) of the H gene cluster result in genetic modifications gial and endothelial cell activation as well

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Figure 1. Overview of complement activation and effector pathways and morphologic changes in aHUS and C3 glomerulopathy. (A) Complement activation occurs via three pathways, the alternative pathway (AP), the lectin pathway (LP), and the classic pathway (CP), which are initiated on surfaces. The type of surface influences activation and the regulator repertoire decides on cascade progression or inhibition. The LP and CP are activated on surfaces by specific carbohydrate moieties (LP), by surface-deposited components (e.g.,C reactive protein, Pentraxin), and by IgGs (CP). A repertoire of regulators controls cascade progression in the fluid phase and on surfaces. The three pathways form specific surface-bound convertases; the AP results in the generation of AP-C3 convertase and the LP/CP trigger formation of the CP C3 convertase. The general role of both C3 convertases is to cleave the abundant plasma protein C3 (concentration 1000–1500 mg/ml) into the anaphylatoxin C3a and the opsonic C3b. The enzymatic response on the first enzymatic levels is frequently enhanced by the potent self-amplifying amplification loop. When activation proceeds the C3 convertases attach an additional C3b fragment, form the C3bBbC3b complex, changes substrate specificity and form a C5 convertase. C5 convertases of the AP and of the LP/CP pathways exist. The major role of the C5 convertase is to cleave C5 (plasma concentration 350 mg/ml) into the powerful anaphy- latoxin C5a and to generate a surface-binding C5b. C5b subsequently initiates the TCC, which forms lytic pores. (B) Structure of an intact glomerulus. Top: Schematic view of mesangial area (green color) in the filtration unit with endothelial cells (blue), GBM (gray), and po- docytes (yellow color). Bottom left: PAS staining of an intact pretransplant kidney. Right: Electron microscopic analysis of a pretransplant kidney with intact glomerular structure. (C) Glomerular changes in aHUS. Top: Schematic presentation of hypocellularity due to cell lysis and loss of endothelial and mesangial cells. Bottom left: PAS staining. Right: EM imaging reveals a pattern of thrombotic microangiopathy. (D) C3 glomerulopathy showing a proliferative pattern with hypercellularity and influx of infiltrating cells. Top: Schematic view of me- sangial proliferation and thickening of GBM in MPGN (right glomerulus) and in DDD (left glomerulus). Bottom left: Glomerular changes revealed by PAS staining. Right: EM image showing thickening of the GBM and double contour formation. as proliferation, leading to influx of activated endothelial and mesangial cells multilayering, as well as mesangial matrix macrophages and to endocapillary and form new matrixes leading to thickening increase. This glomerular remodeling mesangial hypercellularity. Constantly of the GBM and double contours or leads to the typical lobular appearance

JASN 31: 241–256, 2020 CFHR genes in kidney diseases 243 REVIEW www.jasn.org that is summarized under the umbrella in the regulators of complement activa- observations) (Figure 2, left panel). The term MPGN.5 tion region.19,21 The five CFHR genes are segmental duplicated regions can include positioned downstream of the Factor H coding regions, e.g., the repeat regions B gene and are arranged in the order and B’ include exons that encode the THE FACTOR H–CFHR GENE CFHR3, CFHR1, CFHR4, CFHR2,and C-terminal SCRs of Factor H and FHR1, CLUSTER, FHR PROTEINS, AND CFHR5.19 This cluster presents an insta- respectively (see below).25 CONFORMATION ble, dynamic chromosomal region and a CFHR genes are conserved in evo- hotspot for structural rearrangements. The lution indicating essential biologic The Human Factor H–CFHR Gene human CFHR gene cluster includes in- functions.24,26 The four mouse genes Cluster terspersed duplicated regions with strong mCFHR-A, mCFHR-B, mCFHR-C,and The human Factor H–CFHR gene cluster nucleotide identity22–24 (H. Richter, mCFHR-D differ in structure, domain is located on human 1q32 C. Skerka, and P. Zipfel, unpublished composition, and sequence from the

Figure 2. The human Factor H–CFHR gene cluster and the FHR, Factor H protein family. The human Factor H–CFHR gene cluster includes the Factor H gene and the five CFHR genes, which are located on chromosome 1q32. Left side: The CFHR genes are positioned downstream of the Factor H gene (bottom) and are arranged in the order CFHR3, CFHR1, CFHR4, CFHR2,andCFHR5. The human CFHR gene cluster includes interspersed duplicated regions, or segmental duplication elements, which have a high sequence identity and are shown as colored bars below the gene structure. Middle segment: Proteins. Domain organization of the secreted FHR proteins and of Factor H gene products FHL1 and Factor H. Each SCR domain is indicated and the domains of each protein are consecutively numbered. Attached carbohydrate side chains are shown above by the tree-like structure. Constitutively attached carbohydrate side chains have black lines, and facultatively attached carbohydrates have gray lines. The N-terminal multimerization domains of FHR1, FHR2, and FHR5 represented by two SCRs are filled with dashed lines. The C-terminal surface-binding regions of FHR1 and the surface-binding regions of

Factor H and FHL1 are shown with a stippled pattern. FHR1: L290A296 indicates the two FHR1-specific residues, which differ from that of Factor H. Bottom: The human Factor H gene encodes two fluid-phase C3 convertase inhibitors, FHL1 and Factor H. The complement regulatory region is located in SCRs 1–4, is shown by the orange patterns, and is shared by FHL1 and Factor H. The C-terminal recognition regions, i.e.,SCRs6–7 (FHL1/Factor H) and SCRs 19–20 (Factor H), are shown by blue patterns. The Factor H–specific two amino acids

S1191V1196 in the most C-terminal recognition region are shown in the box below SCR 20. FHL1 has a unique six–amino-acid extension that follows SCR 7. Right side: Identified major functions of each FHR protein and of Factor H and FHL1.

244 JASN JASN 31: 241–256, 2020 www.jasn.org REVIEW human genes.25–27 These substantial dif- region with Factor H and has a surface- also involve the Factor H gene (Figure 3, ferences make it difficult to predict the binding site in SCRs6–7 (Figure 2). Supplemental Table 1). FHR variants, as mouse homologs of the human FHR well as FHR1::Factor H and Factor protein.26,28 Similar to the MCP/CD46 H::FHR hybrids, are expressed and the (human) versus Crry (mouse) situation, CFHR GENE VARIATIONS IN AHUS FHR, as well as the Factor H plasma in- mouse FHR homologs need to be identi- ventories, are altered, but FHL1 mRNA fied by functional studies. aHUS is defined by the triad hemolytic is transcribed from the defective Factor anemia, thrombocytopenia, and renal H allele. Four types of modifications ex- FHR Proteins Are Emerging damage. The disease develops in pediat- ist: (1) deletions of chromosomal seg- Complement Modulators and ric and in adult patients, and the clinical ments resulting in Factor H::CFHR3 or Represent Immune and symptoms that are associated with the (2) Factor H::CFHR1 hybrid genes, (3) Inflammatory Regulators with various subforms and patient manage- insertions of chromosomal segments Common and Unique Features ment are summarized in excellent re- generating extra CFHR1::Factor H hy- CFHR genes are mainly transcribed in views.3,37 aHUS is a rare disease and brid genes, or (4) homozygous deletions the liver and the proteins are distributed the frequency is one patient in a popula- of the CFHR3-CFHR1 or CFHR1-CFHR4 in plasma. The five FHR proteins share tion of 500,000 (https://ghr.nlm.nih.gov/ gene segments. Similar, but not identical, structural homology with each other and condition/atypical-hemolytic-uremic- scenarios were identified in unrelated with Factor H and the homology of sin- syndrome). families. gle domains ranges from 35% to .90% HUS has many causes, and includes (Figure 2, middle panel).25–27 Domains STEC-HUS caused by infections with ad (i) Factor H::CFHR3 hybrids. Factor with high homology can share overlap- Shiga toxin–producing Escherichia coli, H::CFHR3 hybrid genes result from ping ligand-binding profiles and func- pneumococcal HUS due to infections chromosomal deletions. One scenario tions. However, domains with low with Streptococcus pneumoniae, and is a Factor H::CFHR3 hybrid gene that and especially the aHUS.9,38,39 The latter is also termed ge- has Factor H exons i-xxii linked to the different numbers of SCR domains of netic aHUS and accounts for about 10% complete CFHR3 gene46 (Figure 3A, the FHR proteins indicate unique of total HUS cases. About 50%–60% of upper line). The encoded 186-kDa, functions. patients with genetic aHUS have alter- 24-domain protein has Factor H1–19 FHR proteins are emerging comple- ations in one or several complement attached to FHR3. A related hybrid ment modulators, activators, and im- genes,40–43 as well as in the DGKe (diacyl gene, with a different chromosomal mune regulators. Each FHR protein glycerine Kinase epsilon) gene, which breakpoint and generated by de novo binds to C3b, iC3b, C3dg, and C3d. encodes a cytoplasmic signaling protein, deletion, codes for a Factor H1–17::FHR3 Some, but not all, FHR proteins interact and in the INF2 (Inverted Formin 2) protein composed of 22 domains47 with ligands such as glycosaminogly- gene, an intracellular actin binding pro- (Supplemental Table 1). Both Factor cans, monomeric CRP, pentraxin-3, the tein.44,45 Thus, the affected genes code H::FHR3 hybrids harbor the N-terminal lipid peroxidation product MDA (ma- for complement proteins that (1)form regulatory region, lack the C-terminal londialdehyde), and laminins of the kid- the alternative pathway C3 convertase (C3, recognition region of Factor H, and ney, and bind to the surfaces of apoptotic Factor B), (2) regulate this central comple- have instead full-length FHR3 added and necrotic cells.29–32 Often, two or ment enzyme (Factor H, MCP/CD46, Fac- at the C terminus. The hybrid proteins more SCR domains form functional tor I), (3) encode modulators (FHR1, are expressed in plasma. The Factor units or ligand-binding segments, in- FHR3, FHR4, thrombomodulin), and H1–19FHR3 hybrid has cofactor activ- cluding dimerization, multimerization, (4) code for TCC inhibitor (vitronectin) ity, and binds with high intensity to or cell binding. Extensive domain map- or for cytoplasmic proteins. For more de- immobilized C3b and heparin result- ping for all five FHR proteins is necessary tailed information on the genetic causes ing in defective surface binding and to localize such binding and interaction of aHUS see the excellent reviews that regulation.46 Also, the highly related 3,37 domains. summarize these complex issues. Factor H1–17::FHR3 hybrid shows im- FHR proteins show sequence homol- CFHR–Factor H gene alterations are paired surface binding and defective ogy and share domains with the central identified in aHUS.3,37,46–58 Here, we de- surface regulation.47 Both hybrid genes fluid-phase regulator Factor H and also scribe how the various CFHR1, CFHR3, allow transcription of FHL1 mRNA, and with FHL1. Factor H acts as a cofactor and Factor H gene alterations affect pro- FHL1 is present in plasma. These ge- for the complement protease Factor I tein structure, protein function, and the nomic settings alter the FHR, Factor H and regulates the stability of the C3 con- FHR and Factor H plasma repertoire. plasma inventory in the same manner. vertase.33,34,35 FHL1 is also encoded by FHR3 and Factor H plasma levels are Factor H gene and the FHL1 mRNA is CFHR Copy Number Variations reduced and intact proteins are encoded generated by alternative splicing.36 In aHUS, chromosomal changes affect by the second, intact allele. CFHR1, FHL1 shares the regulatory N-terminal one or several CFHR genes and may CFHR2, CFHR4,andCFHR5 genes are

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Figure 3. CFHR gene variations in aHUS and aHUS-associated FHR protein variants. (A) Deletion of chromosomal segments: Factor H::CFHR3 hybrid gene. Genetic deletion generating a Factor H::FHR3 hybrid gene (left side) and the corresponding Factor H::FHR3 hybrid variant are shown using the color code of Figure 2. The deleted chromosomal segment is shown with the box with red, stippled lines. (B) Insertional mutagenesis (duplications) of chromosomal segments generating a CFHR1::Factor H hybrid gene. Genetic dupli- cation (boxes with blue lines) generates an extra CFHR1::Factor H hybrid gene together with an extra CFHR3 allele (left side), and the corresponding FHR1::Factor H hybrid protein is shown. The changes affect the FHR plasma repertoire (see Table 1). (C) In patients with DEAP-HUS, the deletion of CFHR3-CFHR1 is often associated with the formation of autoantibodies that bind to the C terminus of Factor H.

48,49 present in two copies and the corre- Table 1). A related hybrid gene, caused (Factor HL1191A1197). The pa- sponding proteins are expressed at by de novo deletion, has a different tients have reduced Factor H, FHR3, normal levels (Figure 3). breakpoint and has Factor H exons and FHR1 plasma levels and normal i–xxii linked to CFHR1 exon vi49 (Sup- FHR4, FHR2, and FHR5 levels (Figure 3, ad (ii) Factor H::FHR1 hybrids. A Factor plementalTable1).Again,FHL1mRNA Table 1). H::CFHR1 hybrid gene that has Factor is transcribed from the hybrid genes. H exons i–xxi (SP, Factor H1–18) Both hybrid proteins, i.e.,Factor ad (iii) Extra FHR1::Factor H hybrids. linked to CFHR1 exons v-vi (FHR14–5) H1–18::FHR14–5 and Factor H1–19::FHR15, Chromosomal duplications generat- was reported in a UK family with eight have the FHR1-specificC-terminal ing an extra CFHR1::Factor H hybrid 48 affected individuals (Supplemental residues and represent Factor HLA gene and a third CFHR3 allele were

Table 1. CFHR Gene Variations in aHUS Affect FHR and Factor H but not FHL1 Plasma Levels Affected Intact Variable Intact FHL1 Factor H FHR3 FHR1 FHR 4 FHR2 FHR5 Factor HFHR3 100 50 Factor HFHR3 50 100 100 100 100 Factor HFHR3 100 50 Factor HFHR3 50 100 100 100 100 Factor HFHR1 100 50 Factor HFHR1 100 50 100 100 100 Factor HFHR1 100 50 Factor HFHR1 100 50 100 100 100 FHR1::Factor H 100 100 FHR1::Factor H 150 100 100 100 100 FHR1::Factor H 100 100 FHR1::Factor H 150 100 100 100 100 DDFHR3FHR1 100 100 0 0 100 100 100 DFHR3FHR1 100 100 50 50 50 100 100 DDFHR1FHR4 100 100 100 0 0 100 100 Numerical data presented as % plasma levels.

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reported as de novo50 and as familial (2) chromosomal duplications, and (3) levels, and altered complement plasma cases.51 The de novo case had an extra homozygous FHR1-FHR3 deficiency. ad levels. Kidney function decreases with chromosomal segment, consisting of (i) chromosomal deletions generate Fac- time and within 10 years about 50% of Factor H exons xxii-xxiii,theCFHR3 gene, tor H::CFHR3 or Factor H::CFHR1 hybrid patients progress to ESKD. Two major and CFHR1exonsi–iv50 (Figure 3B). In genes and the encoded hybrid proteins forms are separated, DDD and C3 GN, the familial scenario, the 49-year-old have the N-terminal regulatory region to- which form related kidney problems.61,62 patient and the affected 20-year-old gether with additional Factor H domains Precise diagnosis requires kidney biopsy daughter had a chromosomal segment linked to either FHR3 or the recognition specimens. This heterogeneous disease is duplicated that includes Factor H exon region of FHR1. The hybrid proteins show induced by various triggering events that xxiii, the CFHR3 gene, and CFHR1 normal Factor H regulation in the fluid lead to complement activation in the exons i–v51 (Supplemental Table 1). phase and lack Factor H surface binding, fluid phase and on glomerular surfaces, Thus, duplicated segments are inserted but use FHR3 or FHR1 domains for surface thus explaining a link of defective alter- within either the B or B’ segmented binding. Intact FHL1 mRNA is transcribed native complement and proteinuria and duplicated elements of the CFHR gene from the mutant allele. ad (ii) duplications hematuria. The genetic and autoimmune cluster. The CFHR1::Factor H hybrid result in extra CFHR1::Factor H hybrid causes are carefully summarized in recent 63–65 genes encode an extra FHR11–3::Factor genes. The encoded FHR1SV protein has outstanding reviews . Here, we focus H19–20 (or FHR11–4::Factor H20)termed dual character. This Janus-faced protein on CFHR copy number variations in the FHR1SV and the extra CFHR3 allele combines the N-terminal dimerization context of an intact Factor H gene, which results in elevated FHR3 plasma levels region of FHR1 with the C-terminal rec- represent a specific genetic form of C3 (150%) (Figure 3B). Plasma levels of ognition region of Factor H. The protein glomerulopathy. All five CFHR genes FHR1, FHR2, FHR4, FHR5, Factor H, lacks the discriminatory part of the can be affected and in this case the Factor and FHL1 are normal. The hybrid FHR1, specifically the LA residues. The H gene remains intact. Mutant FHR pro- protein with the Factor H–specific chromosomal duplications also generate teins are expressed and the FHR plasma C-terminal residues has a Janus-faced a third CFHR3 allele, resulting in higher repertoire is disturbed, whereas Factor H character. FHR1SV forms multimers FHR3 plasma levels. ad (iii) homozygous and FHL1 levels are normal. with itself and with FHR1 and FHR2, deletion of an approximately 24-kb chro- and does compete with Factor H for mosomal segment that encompasses the CFHR Gene Variations in C3 – surface binding.50 52 CFHR3-CFHR1 genesisobservedin Glomerulopathy about 15% of predominantly young pa- Chromosomal Deletions tients with aHUS (Figure 3C).22,55–58 For A 26-year-old Italian patient diagnosed Frequency of CFHR Gene Mutations these patients with DEAP-HUS, this ge- with DDD showed variations in several in aHUS netic scenario is frequently associated CFHR genes.63 A deletion on one allele In the Spanish cohort of 513 patients with the presence of autoantibodies that generates a CFHR3i-iv::CFHR4ix,x hybrid with aHUS, six patients (1.2%) ex- bind to the C-terminal region of Factor H gene that encodes an FHR31–3::FHR48,9 53 pressed FHR1SV variants. In an Italian (SCRs 19–20) and block surface bind- hybrid protein (Supplemental Table 1). aHUS cohort (154 patients), seven pa- ing.23,56– 59 The exact mechanisms The second allele has the common tients (4.5%) had heterozygous CFHR whereby in HUS the homozygous defi- CFHR3::CFHR1 deletion. In addition, the gene rearrangements.54 Five patients ciency of CFHR1 and CFHR3 breaks tol- patient has two heterozygous mutations presented with Factor H::FHR1 hybrids erance and induces antibody production (p.Q211X and p.R2543)intheCFHR2 (2.8%); two patients showed the extra are not clear. However, one link is that gene that terminate transcription. This re- FHR1SV hybrid and a third the CFHR3 FHR3 binds to the C3d fragment and sults in a unique plasma repertoire with an allele (1.3%) and altered FHR1/FHR3 blocks the adjuvant effect of C3d in FHR3::FHR4 hybrid protein; lack of FHR1, plasma levels.54 B cell activation.60 FHR2, and FHR3; reduced FHR4 levels; and normal FHR5, Factor H, and FHL1 Functional Consequences of CFHR plasma levels. Gene Alterations GLOMERULOPATHY DUE TO In an Indian family, the 8-year-old Familial or de novo modifications gener- CFHR GENE VARIATIONS index patient diagnosed with glomerul- ating heterozygous CFHR gene variants opathy histologically classified as an cause aHUS and identify a role of FHR C3 glomerulopathy is a very rare disorder overlap of C3 GN and DDD has a chro- variantproteinsindiseasepathology. affecting 1–2 people per million people mosomal deletion that spans from The CFHR1, CFHR3,andFactor H genes worldwide and is equally common in CFHR1v to the CFHR5-gene promoter.64 are affected; FHR variants are expressed; men and women (https://ghr.nlm.nih.gov/ The CFHR1i-iv::CFHR5 hybrid gene en- and the FHR, Factor H plasma repertoire condition/c3-glomerulopathy). C3 glomer- codes a 90-kDa FHR11–3::FHR5 protein, is altered (Table 1). Three CFHR scenarios ulopathy is frequently associated with pro- and is associated with low FHR1, cause aHUS: (1) chromosomal deletions, teinuria, hematuria, high creatinine plasma FHR2, FHR4, and FHR5 plasma levels

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(Supplemental Table 1). The father and C3b, C5b-9 deposition, and FHR5, as mutant gene with two transcription start a 3-year-old sister have this deletion on well as properdin staining.65 This sites (Figure 4B).66 The upstream pro- one allele, combined with the common FHR212FHR5 hybrid protein with two moter generates a longer transcript, CFHR1-CFHR3 deletion on the second multimerization domains forms large olig- which codes FHR11–2FHR1. The mutant allele. Both patients lack FHR1, and omers, consisting of FHR21–2FHR5, proteins with two multimerization seg- have reduced FHR3, FHR2, FHR4, and FHR1,FHR2,andFHR5,andformsahy- ments form large oligomeric complexes FHR5 plasma levels. The hybrid protein, peractive fluid-phase C3 convertase that with other FHR proteins, which enhance with two interacting regions, forms large consumes C3. In addition, the surface- hemolysis (Supplemental Table 1). oligomers, which include the hybrid, boundhybridanchorsproperdinand A 12-year-old boy with an upper re- FHR1, FHR2, and FHR5. serves as a hyper-amplifier of complement. spiratory tract infection by Haemophilus Two related German patients diagnosed influenza from another Spanish family with MPGN-II had a heterozygous dele- Insertional Mutagenesis of Intragenic diagnosed with C3 glomerulopathy had tion of a 24-kbp chromosomal segment, Segments a heterozygous intragenic duplication in resulting in a CFHR2i-iii::CFHR5 hybrid Two scenarios are reported for Spanish one CFHR1 allele combined with the gene that encodes an FHR212::FHR5 hy- patients with C3 glomerulopathy, which CFHR3-CFHR1 deletion on the second brid protein.65 FHR2 and FHR5 plasma add new genetic material in the CFHR1 allele.67 Duplication of exons i-v results levels are reduced, whereas FHR1, FHR3, gene. One patient diagnosed with C3 in an FHR1 mutant protein composed of FHR4, FHL1, and Factor H levels are glomerulopathy has in one CFHR1 allele nine SCRs (Figure 4B). The patients have normal (Figure 4A). The kidney biopsy a duplication, which includes the CFHR1 normal FHR2, FHR3, FHR4, FHR5, specimens from both patients showed promoter and exons i-iii, resulting in a FHL1, and Factor H levels. The affected

A

B

C

Figure 4. CFHR gene variations in C3 glomerulopathy and associated FHR protein variants. (A) Deletion of large chromosomal segments. Deletion of a large chromosomal segment, which includes exons of the CFHR2 gene and the intragenic region spanning to the CFHR5 gene, generates a CFHR2::CFHR5 hybrid gene. This gene encodes an FHR21–2::FHR5 hybrid protein which is shown on the right. (B) Insertional mutation of intragenetic segments: Duplication of CFHR1 gene segments results in an FHR1 mutant protein. Duplication of the

first three exons results in a mutant CFHR1 gene. The encoded protein FHR11–2FHR1 has duplicated interaction segments (right panel). (C) Insertional mutageneses of chromosomal segments results in extra hybrid genes. A duplicated extra gene has CFHR3 exons i–iii linked to the last exons of the CFHR1 gene and generates a new CFHR3::CFHR1 hybrid gene that encodes an FHR31–2::FHR1 hybrid protein.

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CFHR individuals have low C3 plasma levels Table1).TheencodedFHR51–2::FHR2 GENE CLUSTER and the kidneys showed intense C3 de- protein forms large oligomers, which VARIATIONS IN OTHER (KIDNEY) position, mesangial hypercellularity, and include the hybrid, FHR1, FHR2, DISEASES osmiophilic deposits along the GBM. and FHR5. The FHR11–4FHR1 mutant forms large IgAN oligomers, which include the mutant, Glomerulopathy due to CFHR Gene CFHR1, CFHR3,andCFHR5 gene modifi- FHR1, FHR2, and FHR5, and which Variations cations and variations of FHR plasma levels bound with higher intensity to surface- The eight scenarios show heterozygous cause pathology in IgAN and these scenar- attached C3b and acted as effective com- variations and are familial. Three scenar- ios develop in the context of intact Factor H petitors for Factor H. ios result from deletion of large genomic and FHL1.76–79 In addition, Factor H genet- FHR5::FHR5 mutants with dupli- segments. Two cases combine the dele- ic variations apparently influence comple- cated SCRs1–2 were reported in patients tion with heterozygous CFHR3-CFHR1 ment regulation in IgAN.80,81 Furthermore, of a large Cypriote cohort, who presented deletion on the second allele. Two Indian mutations in another complement gene, with microscopic hematuria, synphar- patients, but not the index patient, com- such as the MBL gene, are reported in yngitic macroscopic hematuria, and C3 bine the CFHR4::CFHR2 and CFHR3- IgAN.82 Genome-wide association stud- GN, and showed slightly reduced C3 CFHR1 deletions. The Italian patient ies identified the CFHR gene cluster as a plasma levels.68–70 Kidney biopsy spec- combines the mutations with CFHR2 susceptibility locus in IgAN and oppos- imens revealed mesangial matrix ex- gene mutations. Two case scenarios ing effects are reported.83 Homozygous pansion, capillary wall thickening, from Spain show duplications in the CFHR1/CFHR3 deletion resulting in the and glomerular C3, as well as C1q, CFHR1 gene, the Cypriot patients have absence of FHR1 and FHR3 in plasma is IgA, and IgG staining combined with a CFHR5 gene duplication, and two protective.84–86 In addition, CFHR5 is an subendothelial electron dense deposits.70 other duplications result in extra IgAN susceptibility gene and mutant FHR5 In the CFHR5 gene, the patients have CFHR3-CFHR1 or CFHR5-CFHR2 hy- proteins show altered C3b binding.87 Cur- exons i-iii duplicated (Supplemental brid genes (Supplemental Table 1). rent work in IgAN is focusing on FHR1 and 88–91 Table1).TheFHR51–2FHR5 mutant CFHR gene variations cause C3 glo- FHR5 plasma levels. Elevated FHR1 and protein has two multimerization do- merulopathy and the disease develops also FHR5 plasma levels and higher mains. An almost identical duplication in the context of an intact Factor H FHR1::Factor H ratios influence alternative of CFHR5 exons i-iii was identified in gene and presence of Factor H in pathway regulation, and correlate with glo- UK family of non-Cypriote origin. The plasma. One principle is emerging: merular filtration and disease severity.91 patients expressed the same FHR51–2FHR5 CFHR gene variations in C3 glomerul- mutants in plasma.71 Both the Cypriote opathy result in variant proteins that CFHR5 Gene Variations in Other and the UK patients have reduced FHR5 have two interaction segments, and Kidney and Retinal Diseases plasma levels. All other FHR proteins, for several proteins formation of large Sequence variations in the CFHR5 gene FHL1, and Factor H are present at normal oligomeric complexes is shown. Thus, are also reported in aHUS,91–93 in C3 levels. FHR mutant proteins and together with glomerulopathy/DDD,94 for a case with altered FHR plasma levels in the con- S. pneumoniae infection,95 and for the Duplication of Extra Gene Segments text of an intact Factor H gene cause retinal disease AMD.96 For these scenar- Insertion of an extra CFHR312::CFHR1 glomerular pathology (Supplemental ios it will be necessary to address hybrid gene between the FHR3 and Table 1). whether all reported changes are patho- FHR1 genes was reported in a UK family.72 genic or whether the exchanges repre- The affected members had the biopsy- Distinct Genetic Scenarios Cause sent rare polymorphic variants. based diagnosis of MPGN. All five CFHR Related Glomerular Changes genes and the Factor H gene are intact; C3 glomerulopathy is caused by dis- FHR Protein Deposition in Fibrillary thus, the FHR31–2FHR1 hybrid is ex- tinct genetic scenarios; e.g., by hetero- GN and Pauci-Immune Kidneys pressed together with the five FHR pro- zygous CFHR gene mutations in the Proteome analyses identified FHR1, teins, FHL1, and Factor H (Figure 4C). context of intact Factor H alleles and FHR2, and FHR5 deposition in glomeruli The renal biopsy specimens showed also by homozygous (or compound- of patients with the rare kidney disease C3b staining, glomerular inflamma- heterozygous) Factor H gene muta- fibrillary GN along with strong deposition tion, and a membranoproliferative tions and intact CFHR genes. Thus, of DNA-JB997 and in pauci-immune nec- type III pattern. alterations in different genes cause rotizing crescentic GN.98 A CFHR5::CFHR2 hybrid gene was the same or highly related glomerular identified in a US patient with familial alterations and the same patholo- The Challenge of Homozygous C3 glomerulopathy.73 This extra hybrid gies,20,74,75 and highlight the role CFHR1-CFHR3 Deletion gene has CFHR5 exons i-iii (SP, SCRs1,2) of FHR proteins as complement Homozygous CFHR1-CFHR3 deficiency has attached to the CFHR2 gene (Supplemental modulators. many faces: it confers risk in DEAP-HUS,23

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99 in SLE, and for infections with the Factor HLA, with the FHR1LA residues, oligomeric complexes is reported, which Gram-negative bacterium Neisseria cause aHUS.105–107 enhance complement activity. meningitidis,100 but has protective effects Furthermore, FHR1, FHR2, and in IgAN78 and AMD.101,102 Importantly, FHR Plasma Levels FHR4A are integrated into lipid parti- homozygous CFHR1-CFHR3 deficiency CFHR cluster variations result in unique cles, which also include ApoE, ApoAI, is not a risk or protective marker on its FHR–Factor H plasma profiles (Tables 1 ApoB100, LPS-binding protein, fibrinogen, own. Homozygous CFHR1-CFHR3 defi- and 2). FHR plasma concentration is a and other uncharacterized proteins.118,119 ciency is present in 5%–8% of healthy timely topic because plasma levels re- Thus, unique interaction profiles and a whites and the frequency is even higher ported for healthy individuals vary by preference for interacting partners indi- in the healthy Asian (approximately up to two orders of magnitude.108–112 cate different regulatory roles of FHR 18%) and African populations (approxi- For example, FHR1 plasma levels range oligomers (Figure 5B). mately 28%).103,104 from 0.2 mg/ml to 120 mg/ml.76,108–110,113 Complex formation of FHR proteins and Payload Composition Influences association of FHR proteins in lipoprotein Oligomer Function FHR VARIANTS PROVIDE CLUES particles (see below) may explain such The disease-associated FHR mutants ON FHR PROTEIN FUNCTION AND variations and also indicate assay-based (FHR1::FHR1, FHR1::FHR5, FHR5::FHR5) IDENTIFY PATHOLOGIC ROLES OF detection aspects. and hybrids (FHR1::FHR5-, FHR2::FHR5, FHR OLIGOMERS FHR5::FHR2) form oligomers that con- FHR Proteins Form Multimers that tain the specificFHRvariant,FHR1, CFHR gene alterations cause pathology, Show a Preference for Interaction FHR2, and FHR5. Apparently, payload which can manifest in different tissues, Partners composition and the combinations of and variations within the same CFHR The SCR backbone provides flexibility. functionally distinct FHR proteins influ- gene can cause different pathologies in FHR proteins apparently interact with ence oligomer function (Figures 5, C and tissue compartments. Parameters af- themselves, with other FHR proteins, D and 6).65–68 fected include the following categories and potentially also with Factor H, and bind to C3b and to plasma and cell sur- FHR Proteins as Biomarkers for The C Terminus of FHR1 face constituents. In physiologic set- Diagnosis and Therapy FHR1 and Factor H share almost identi- tings, FHR proteins and also Factor H CFHR gene variations define specificge- cal three C-terminal SCRs that include adapt various conformations and can netic forms that integrate in the overall the recognition regions. Thus, FHR1 and form dimers, tetramers, or multimers disease spectrum of aHUS and C3 glo- Factor H bind the same or related targets (Figure 5A).58,66,67,111–115 Such multi- merulopathy. The current diagnosis for and together fine-tune local complement mers enhance regulatory action; for ex- C3 glomerulopathy is on the basis of action. However, the most C-terminal ample, Factor H mini-variants, which are kidney biopsy specimens. However, for SCRs of FHR1 and Factor H differ; linked via an FHR1 multimerization re- both disorders minimal invasive diag- FHR1LA uses L290,A296 in SCR5 and Factor gion, are more potent in complement nostic approaches are advantageous 116,117 HSV, S1191,V1197 in SCR20 (see Figure 2). control. For both FHR1 mutants for biomarker profiling. Exchange of the two residues LA and SV with duplicated interaction segments,67,68 CFHR gene variations are valuable ge- 65 has pathologic consequences; FHR1SV, for the FHR1-FHR5, and also for the netic markers and, when combined with 66 with the Factor HSVresidues, and similarly FHR2::FHR5 hybrid formation of large altered FHR protein mobility, variations

Table 2. CFHR Gene Variations in C3 Glomerulopathy affect FHR Plasma Levels, but not Factor H and FHL1 plasma levels Intact Affected Variable FHL1 Factor H FHR3 FHR1 FHR 4 FHR2 FHR5 FHR3::FHR4 100 100 0 FHR3::FHR4 0 50 100 Mutated 100 FHR1::FHR5 100 100 100 50 FHR1::FHR5 50 50 50 FHR1::FHR5 100 100 50 0 FHR1::FHR5 50 50 50 FHR2::FHR5 100 100 100 100 100 50 FHR2::FHR5 50

FHR1::FHR1 100 100 100 50 FHR1::FHR1 100 100 100 FHR1::FHR1 100 100 100 50 FHR1::FHR1 100 100 100 FHR5::FHR5 100 100 50 50 100 100 FHR5::FHR5 50

FHR3::FHR1 100 100 100 FHR3::FHR1 100 100 100 100 FHR5::FHR2 100 100 100 100 100 100 FHR5::FHR2 100 Numerical data presented as %.

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A B C D

Figure 5. FHR proteins form homodimers and heterodimers; FHR hybrid proteins with two multimerization segments form oligomers. (A) The three proteins FHR1, FHR2, and FHR5 form dimers via their N-terminal domains (gray domains). The N-terminal multi- merization segments of each FHR protein interact with a second protein and form dimers and even multimers. FHR1 and FHR2 can form heterodimers. (B) FHR proteins are contained in lipid complexes. FHR1, FHR2, and FHR4-A are associated with lipids HDL and LDLD. Lipids include FHR1 and FHR2 together with ApoAI, LPS-binding protein, fibrinogen, and additional so-far-uncharacterized proteins. FHR4-A is present in triglyceride-rich lipid particles, which also include ApoE, ApoAI, ApoE, ApoAIV, ApoB48, and ApoB100. (C) The FHR1 mutants with two interaction sites form larger complexes. Upper panel: A single FHR1::FHR1 mutant with two interaction segments that bind FHR1, FHR2, and FHR5 and allow formation of larger complexes. Oligomerization or branching is disrupted when FHR1, FHR2, or FHR5 with one interaction segment is integrated. (D) The FHR2::FHR5 hybrid forms larger complexes. Upper panel: A single FHR2::FHR5 hybrid has two interaction segments that allow formation of larger complexes. The FHR2::FHR5 hybrid protein can multimerize via theFHR2(upperconstellation)orvia the FHR5 multimerization domain with FHR5 (bottom sce- nario). Oligomerization or branching is disrupted when FHR1 or FHR2 with one interaction segment is attached to the FHR2 domain, or when FHR5 is bound to the FHR5 domain. of FHR plasma levels provide important CONCLUSIONS, PERSPECTIVE, surfaces activates the inflammasome. diagnostic information. FHR plasma lev- AND FUTURE DIRECTIONS The unique roles of the individual FHR els, the evaluation of complement split proteins in the complete cascade suggest products, TCC levels, complement activ- CFHR–Factor H gene cluster variations that patients with CFHR gene defects ity, and C3 levels allow monitoring of are associated with several kidney disor- may benefit from treatment with one complement in a direct and timely man- ders, including aHUS, C3 glomerulop- of the new complement inhibitors that ner. Such parameters can also be used athy, and also IgAN. These associations are currently in development.122 evaluate the efficacy of approved comple- show important roles of the FHR pro- The major challenges ahead are (1)to ment therapeutics and new inhibitors that teins in maintaining glomerular integ- link the genetic changes in the CFHR are developed and tested in clinical tri- rity. FHR proteins are complement cluster with precise morphologic and als.120,121 For renal biopsy specimens, a modulators and complement activators, immunohistochemical staining of renal correlation of FHR protein deposition and FHR1 regulates inflammasome ac- biopsy specimens, with cellular and with morphologic alterations and immu- tivity. The proteins act alone, and also morphologic alterations, and with nohistologic staining patterns will pro- cooperate with each other and with Factor plasma biomarkers; (2)tounderstand vide important diagnostic information. H. For example, FHR1 balances the local the exact physiologic role of each FHR In this regard, FHR-specificmABsare action of the complement inhibitor Factor protein; and (3)todefine the interplay advantageous and should be developed. H, and when attached to the necrotic of the FHR proteins as complement

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A BC

Figure 6. FHR mutant and hybrid proteins affect complement regulation at target sites. Gene mutations and copy number variations in the human Factor H–CFHR gene cluster in aHUS and C3 glomerulopathy affect protein structure and protein levels in plasma and influence the fate of complement control at target surfaces. (A) Normal homeotic scenario. FHR1 and Factor H with their homologous C-terminal regions bind to surface-deposited C3b at danger sites and to glycosaminoglycans (GAGs). The proteins are shown and the three C-terminal recognition region is presented, and the FHR1-specific LA and the Factor H–specific SV residues in the most C-terminal do- mains are shown. The balance of FHR1 and Factor H at modified target sites is influenced by the structure of the proteins; by Factor H, FHL1, and FHR plasma levels; by the binding intensities of the proteins to the ligands; and by the density of C3b and the type and composition of GAGs at sites of damage. FHR1 competes with Factor H for surface binding and, in a proper combination, the two reg- ulators adjust and fine-tune local complement action. Thereby, FHR1 initiates inflammasome activation and Factor H dissociates the alternative pathway C3 convertase and inhibits complement progression. (B) Scenarios in aHUS and C3 glomerulopathy. aHUS scenario, left panel: Factor H::FHR3, Factor H::FHR1, and FHR1::Factor H hybrid proteins together with altered plasma levels influence the local FHR1, Factor H balance at a damage surface (left site). C3 glomerulopathy scenario, right panel: The various FHR hybrid and mutant proteins, many of which having two interacting segments and form large oligomeric complexes, influence the local FHR1, Factor H balance at damaged surfaces. Scenarios in aHUS, left panel: Various scenarios in the form of deletions; insertional mutations, including intragene; as well as chromosomal duplications generate CFHR–Factor H or Factor H–CFHR hybrid genes. In aHUS, Factor H and the CFHR1 and CFHR3 genes are affected, but CFHR4, CFHR2,andCFHR5 genes remain intact. Scenarios in C3 glomerulopathy, right panel: Various scenarios in the form of deletions; insertional mutations, including intragene; as well as chromosomal duplications generate CFHR-CFHR hybrid genes. In C3 glomerulopathy all five CFHR genes can be affected, but the Factor H gene remains intact. modulators or amplifiers with each and prognostic parameters for the ACKNOWLEDGMENTS other and with Factor H. A strong FHR-associated disorders. Advanced interdisciplinary approach includ- understanding of the disease mecha- We apologize to all colleagues and groups ing geneticists, complementologists, nisms will guide physicians and pa- whose work and important data could not nephropathologists, and clinicians is tients through this complex disease be cited or discussed in greater detail due to required to establish precise diagnostic spectrum. space limitations.

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The funders had no role in study design, data D, et al.Conference Participants;: Atypical et al.: C3 glomerulonephritis and dense collection and analysis, decision to publish, or hemolytic uremic syndrome and C3 glomer- deposit disease share a similar disease ulopathy: Conclusions from a “Kidney Disease: course in a large United States cohort of preparation of the manuscript. Improving Global Outcomes” (KDIGO) con- patients with C3 glomerulopathy. Kidney troversies conference. Kidney Int 91: 539–551, Int 93: 977–985, 2018 2017 21. Díaz-Guillén MA, Rodríguez de Córdoba S, DISCLOSURES 5. Pickering MC, D’Agati VD, Nester CM, Heine-Suñer D: A radiation hybrid map of Smith RJ, Haas M, Appel GB, et al.: C3 complement factor H and factor H-related – Dr. Zipfel provided advice on complement to glomerulopathy: Consensus report. Kidney genes. Immunogenetics 49: 549 552, 1999 – Vifor Fresenius Medical Care Renal Pharma, Ge- Int 84: 1079 1089, 2013 22. Male DA, Ormsby RJ, Ranganathan S, neric Assays and received speaker honorarium 6. Gharavi AG, Kiryluk K, Choi M, Li Y, Hou P, Giannakis E, Gordon DL: Complement from Alexion. All of the remaining authors have Xie J, et al.: Genome-wide association study factor H: Sequence analysis of 221 kb of fi nothing to disclose. identi es susceptibility loci for IgA nephropa- human genomic DNA containing the entire thy. Nat Genet 43: 321–327, 2011 fH, fHR-1 and fHR-3 genes. Mol Immunol 37: 7. Zipfel PF, Skerka C: Complement factor H 41–52, 2000 and related proteins: An expanding family 23. Zipfel PF, Edey M, Heinen S, Józsi M, FUNDING of complement-regulatory proteins? Immunol Richter H, Misselwitz J, et al.: Deletion of Today 15: 121–126, 1994 complement factor H-related genes CFHR1 8. Medjeral-Thomas N, Pickering MC: The and CFHR3 is associated with atypical The study was supported by the German Re- complement factor H-related proteins. Im- hemolytic uremic syndrome. PLoS Genet search Foundation Deutsche Forschungsgemein- munol Rev 274: 191–201, 2016 3: e41, 2007 schaft, SFB 1192 “Immune mediated glomerular 9. Zipfel PF, Skerka C: Complement regulators 24. Cantsilieris S, Nelson BJ, Huddleston J, diseases”, projects B06 and SK46/2. Dr. Zipfel and and inhibitory proteins. Nat Rev Immunol 9: Baker C, Harshman L, Penewit K, et al.: Re- Dr. Skerka acknowledge support by Kidneeds. The 729–740, 2009 current structural variation, clustered sites research leading to these results has received fund- 10. Hajishengallis G, Reis ES, Mastellos DC, of selection, and disease risk for the com- ing from the European Community’s Seventh Ricklin D, Lambris JD: Novel mechanisms plement factor H (CFH)genefamily.Proc Framework Programme under grant agreement and functions of complement. Nat Immunol Natl Acad Sci U S A 115: E4433–E4442, no. 2012-305608, “European Consortium for 18: 1288–1298, 2017 2018 High-Throughput Research in Rare Kidney Diseases 11. McCullough JW, Renner B, Thurman JM: 25. Skerka C, Chen Q, Fremeaux-Bacchi V, (EURenOmics)”. Dr. Stea was supported by a schol- The role of the in acute Roumenina LT: Complement factor H re- arship from the Società Italiana di Nefrologia. kidney injury. Semin Nephrol 33: 543–556, lated proteins (CFHRs). Mol Immunol 56: 2013 170–180, 2013 12. Coulthard LG, Woodruff TM: Is the com- 26. Vik DP, Muñoz-Cánoves P, Kozono H, SUPPLEMENTAL MATERIAL plement activation product C3a a proin- Martin LG, Tack BF, Chaplin DD: Identifi- flammatory molecule? Re-evaluating the cation and sequence analysis of four com- evidence and the myth. JImmunol194: plement factor H-related transcripts in This article contains the following 3542–3548, 2015 mouse liver. J Biol Chem 265: 3193–3201, supplemental material online at http:// 13. Liszewski MK, Java A, Schramm EC, 1990 jasn.asnjournals.org/lookup/suppl/doi:10.1681/ Atkinson JP: Complement dysregulation 27. Józsi M, Zipfel PF: Factor H family proteins ASN.2019050515-/DCSupplemental. and disease: Insights from contemporary and human diseases. Trends Immunol 29: genetics. Annu Rev Pathol 12: 25–52, 2017 380–387, 2008 Supplemental Table 1. Morphologic dif- 14. Holers VM, Banda NK: Complement in the 28. Antonioli AH, White J, Crawford F, Renner ferences in atypical hemolytic uremic syn- initiation and evolution of rheumatoid ar- B, Marchbank KJ, Hannan JP, et al.: Modu- drome (aHUS) and C3 glomerulopathy. thritis. Front Immunol 9: 1057, 2018 lation of the alternative pathway of com- Supplemental Table 2. Alterations in the 15. Karpman D, Loos S, Tati R, Arvidsson I: plement by murine Factor H-related Factor H–CFHR gene cluster in aHUS/dEAP-HUS Haemolytic uraemic syndrome. JIntern proteins. J Immunol 200: 316–326, 2018 Med 281: 123–148, 2017 29. Zipfel PF, Hallström T, Hammerschmidt S, and C3 glomerulopathy. 16. Sethi S, Fervenza FC: Membranoprolifer- Skerka C: The complement fitness factor H: ative glomerulonephritis--a new look at an Role in human diseases and for immune old entity. NEnglJMed366: 1119–1131, escape of pathogens, like pneumococci. REFERENCES 2012 Vaccine 26[Suppl 8]: I67–I74, 2008 17. Sethi S, Fervenza FC: Pathology of renal 30. Boon CJ, van de Kar NC, Klevering BJ, 1. Zipfel PF, Skerka C, Chen Q, Wiech T, diseases associated with dysfunction of the Keunen JE, Cremers FP, Klaver CC, et al.: Goodship T, Johnson S, et al.: The role of alternative pathway of complement: C3 The spectrum of phenotypes caused by complement in C3 glomerulopathy. Mol glomerulopathy and atypical hemolytic variants in the CFH gene. Mol Immunol 46: Immunol 67: 21–30, 2015 uremic syndrome (aHUS). Semin Thromb 1573–1594, 2009 2. Nester CM, Barbour T, de Cordoba SR, Hemost 40: 416–421, 2014 31. Zipfel PF, Skerka C: FHL-1/reconectin: A Dragon-Durey MA, Fremeaux-Bacchi V, 18. Cook HT, Pickering MC: Histopathology of human complement and immune regulator Goodship TH, et al.: Atypical aHUS: State of MPGN and C3 glomerulopathies. Nat Rev with cell-adhesive function. Immunol Today the art. Mol Immunol 67: 31–42, 2015 Nephrol 11: 14–22, 2015 20: 135–141, 1999 3. Noris M, Mescia F, Remuzzi G: STEC-HUS, 19. Zipfel PF, Skerka C, Hellwage J, Jokiranta ST, 32. Csincsi Á, Kopp A, Zöldi M, Bánlaki Z, atypical HUS and TTP are all diseases of Meri S, Brade V, et al.: Factor H family proteins: Uzonyi B, Hebecker M, et al.: Factor complement activation. Nat Rev Nephrol 8: On complement, microbes and human dis- H-related protein 5 interacts with pentraxin 622–633, 2012 eases. Biochem Soc Trans 30: 971–978, 2002 3 and the extracellular matrix and modu- 4. Goodship TH, Cook HT, Fakhouri F, 20. Bomback AS, Santoriello D, Avasare RS, lates complement activation. JImmunol Fervenza FC, Frémeaux-Bacchi V, Kavanagh Regunathan-Shenk R, Canetta PA, Ahn W, 194: 4963–4973, 2015

JASN 31: 241–256, 2020 CFHR genes in kidney diseases 253 REVIEW www.jasn.org

33. Chen Q, Manzke M, Hartmann A, Büttner M, 45. Bu F, Zhang Y, Wang K, Borsa NG, Jones haemolytic uraemic syndrome (HUS). Thromb Amann K, Pauly D, et al.: Complement MB, Taylor AO, et al.: Genetic analysis Haemost 101: 227–232, 2009 Factor H-Related 5-Hybrid proteins anchor of 400 patients refines understanding and 57. Józsi M, Licht C, Strobel S, Zipfel SL, Richter properdin and activate complement at self- implicates a new gene in atypical hemolytic H, Heinen S, et al.: Factor H autoantibodies surfaces. JAmSocNephrol27: 1413–1425, uremic syndrome. JAmSocNephrol29: in atypical hemolytic uremic syndrome cor- 2016 2809–2819, 2018 relate with CFHR1/CFHR3 deficiency. Blood 34. Rudnick RB, Chen Q, Stea ED, Hartmann A, 46. Francis NJ, McNicholas B, Awan A, Waldron M, 111: 1512–1514, 2008 Papac-Milicevic N, Person F, et al.: FHR5 ReddanD,SadlierD,etal.:AnovelhybridCFH/ 58. Moore I, Strain L, Pappworth I, Kavanagh D, binds to laminins, uses separate C3b and CFHR3 gene generated by a microhomology- Barlow PN, Herbert AP, et al.: Association of surface-binding sites and activates comple- mediated deletion in familial atypical factor H autoantibodies with deletions of ment on malondialdehyde-acetaldehyde hemolytic uremic syndrome. Blood 119: CFHR1, CFHR3, CFHR4, and with mutations surfaces. J Immunol 200: 2280–2290, 2018 591–601, 2012 in CFH, CFI, CD46, and C3 in patients with 35. Hannan JP, Laskowski J, Thurman JM, 47. Challis RC, Araujo GS, Wong EK, Anderson atypical hemolytic uremic syndrome. Blood Hageman GS, Holers VM: Mapping the HE, Awan A, Dorman AM, et al.: A de novo 115: 379–387, 2010 complement Factor H-related protein 1 deletion in the regulators of complement 59. Durey MA, Sinha A, Togarsimalemath SK, (CFHR1):C3b/C3d interactions. PLoS One activation cluster producing a hybrid comple- Bagga A: Anti-complement-factor H-associated 11: e0166200, 2016 ment Factor H/complement Factor H-related 3 glomerulopathies. Nat Rev Nephrol 12: 36. Halder LD, Abdelfatah MA, Jo EA, gene in atypical hemolytic uremic syndrome. 563–578, 2016 Jacobsen ID, Westermann M, Beyersdorf N, J Am Soc Nephrol 27: 1617–1624, 2016 60. Buhlmann D, Eberhardt HU, Medyukhina A, et al.: Factor H binds to extracellular DNA 48. Venables JP, Strain L, Routledge D, Bourn Prodinger WM, Figge MT, Zipfel PF, et al.: traps released from human blood mono- D, Powell HM, Warwicker P, et al.: Atypical FHR3 Blocks C3d-Mediated Coactivation of cytes in response to Candida albicans. Front haemolytic uraemic syndrome associated with Human B Cells. JImmunol197: 620–629, Immunol 7: 671, 2017 a hybrid complement gene. PLoS Med 3: 2016 37. Loirat C, Frémeaux-Bacchi V: Atypical he- e431, 2006 61. Ravindran A, Fervenza FC, Smith RJH, De molytic uremic syndrome. Orphanet J Rare 49. Maga TK, Meyer NC, Belsha C, Nishimura Vriese AS, Sethi S: C3 glomerulopathy: Ten Dis 6: 60, 2011 CJ, Zhang Y, Smith RJ: A novel deletion in years’ experience at mayo clinic. Mayo Clin 38. SzilágyiA,KissN,BereczkiC,TálosiG,Rácz the RCA gene cluster causes atypical he- Proc 93: 991–1008, 2018 K, Túri S, et al.: The role of complement in molytic uremic syndrome. Nephrol Dial 62. Smith RJH, Appel GB, Blom AM, Cook Streptococcus pneumoniae-associated Transplant 26: 739–741, 2011 HT, D’Agati VD, Fakhouri F, et al.: C3 haemolytic uraemic syndrome. Nephrol 50. Eyler SJ, Meyer NC, Zhang Y, Xiao X, Nester glomerulopathy—understanding a rare Dial Transplant 28: 2237–2245, 2013 CM, Smith RJ: A novel hybrid CFHR1/CFH complement-driven renal disease. Nat Rev 39. Meinel C, Spartà G, Dahse HM, Hörhold F, gene causes atypical hemolytic uremic Nephrol 15: 129–143, 2019 KönigR,WestermannM,etal.:Strepto- syndrome. Pediatr Nephrol 28: 2221–2225, 63. Piras R, Martin B, Valoti B, Borsa N, Alberti M, coccus pneumoniae from patients with he- 2013 et al.: Multiple abnormalities in the CFHR- molytic uremic syndrome binds human 51. Valoti E, Alberti M, Tortajada A, Garcia- gene cluster in a patient with DDD. Mol plasminogen via the surface protein PspC Fernandez J, Gastoldi S, Besso L, et al.: A Immunol 67: 171, 2015 and uses plasmin to damage human endo- novel atypical hemolytic uremic syndrome- 64. Togarsimalemath SK, Sethi SK, Duggal R, thelial cells. JInfectDis217: 358–370, 2018 associated hybrid CFHR1/CFH gene en- Le Quintrec M, Jha P, Daniel R, et al.: A 40. Noris M, Caprioli J, Bresin E, Mossali C, coding a fusion protein that antagonizes novel CFHR1-CFHR5 hybrid leads to a fa- Pianetti G, Gamba S, et al.: Relative role of factor H-dependent complement regula- milial dominant C3 glomerulopathy. Kidney genetic complement abnormalities in spo- tion. JAmSocNephrol26: 209–219, 2015 Int 92: 876–887, 2017 radic and familial aHUS and their impact on 52. Goicoechea de Jorge E, Tortajada A, García SP, 65. Chen Q, Wiesener M, Eberhardt HU, clinical phenotype. Clin J Am Soc Nephrol Gastoldi S, Merinero HM, García-Fernández J, Hartmann A, Uzonyi B, Kirschfink M, et al.: 5: 1844–1859, 2010 et al.: Factor H competitor generated by Complement factor H-related hybrid pro- 41. Osborne AJ, Breno M, Borsa NG, Bu F, gene conversion events associates with tein deregulates complement in dense de- Frémeaux-Bacchi V, Gale DP, et al.: Statis- atypical hemolytic uremic syndrome. JAm posit disease. JClinInvest124: 145–155, tical validation of rare complement variants Soc Nephrol 29: 240–249, 2018 2014 provides insights into the molecular basis 53. Abarrategui-Garrido C, Martínez-Barricarte R, 66. Tortajada A, Guitierrez-Tenoria J, Gonzalez of atypical hemolytic uremic syndrome López-Trascasa M, de Córdoba SR, Sánchez- AS, Letosa RM, Bouthelier A, Sanchez-Coral and C3 glomerulopathy. J Immunol 200: Corral P: Characterization of complement P, et al.: Novel duplication of the FHRs di- 2464–2478, 2018 factor H-related (CFHR) proteins in merization domain associated with C3G. 42. Maga TK, Nishimura CJ, Weaver AE, Frees plasma reveals novel genetic variations Mol Immunol 89: 181, 2017 KL, Smith RJ: Mutations in alternative pathway of CFHR1 associated with atypical he- 67. Tortajada A, Yébenes H, Abarrategui- complement proteins in American patients molytic uremic syndrome. Blood 114: Garrido C, Anter J, García-Fernández JM, with atypical hemolytic uremic syndrome. 4261–4271, 2009 Martínez-Barricarte R, et al.: C3 glomerulopathy- Hum Mutat 31: E1445–E1460, 2010 54. Bernabéu-Herrero ME, Jiménez-Alcázar M, associated CFHR1 mutation alters FHR olig- 43. Challis RC, Ring T, Xu Y, Wong EK, Anter J, Pinto S, Sánchez Chinchilla D, omerization and complement regulation. Flossmann O, Roberts ISD, et al.: Throm- Garrido S, et al.: Complement factor H, J Clin Invest 123: 2434–2446, 2013 botic microangiopathy in inverted Formin FHR-3 and FHR-1 variants associate in an 68. Gale DP, de Jorge EG, Cook HT, Martinez- 2-mediated renal disease. J Am Soc Nephrol extended haplotype conferring increased Barricarte R, Hadjisavvas A, McLean AG, 28: 1084–1091, 2017 risk of atypical hemolytic uremic syndrome. et al.: Identification of a mutation in comple- 44. Lemaire M, Frémeaux-Bacchi V, Schaefer F, Mol Immunol 67: 276–286, 2015 ment factor H-related protein 5 in patients Choi M, Tang WH, Le Quintrec M, et al.: 55. Jokiranta TS: HUS and atypical HUS. Blood of Cypriot origin with glomerulonephritis. Recessive mutations in DGKE cause atypical 129: 2847–2856, 2017 Lancet 376: 794–801, 2010 hemolytic-uremic syndrome. Nat Genet 45: 56. Skerka C, Józsi M, Zipfel PF, Dragon-Durey 69. Athanasiou Y, Voskarides K, Gale DP, 531–536, 2013 MA, Fremeaux-Bacchi V: Autoantibodies in Damianou L, Patsias C, Zavros M, et al.:

254 JASN JASN 31: 241–256, 2020 www.jasn.org REVIEW

Familial C3 glomerulopathy associated online ahead of print March 6, 2019]. Ne- et al.: Acute presentation and persistent with CFHR5 mutations: Clinical characteris- phrology (Carlton) doi:10.1111/nep.13580 glomerulonephritis following streptococcal tics of 91 patients in 16 pedigrees. Clin J Am 84. Guo WY, Liu QZ, Zhu L, Li ZY, Meng SJ, Shi infection in a patient with heterozygous Soc Nephrol 6: 1436–1446, 2011 SF, et al.: Coding and noncoding variants in complement factor H-related protein 5 de- 70. Gale DP, Maxwell PH: C3 glomerulone- CFH act synergistically for complement ac- ficiency. Am J Kidney Dis 60: 121–125, 2012 phritis and CFHR5 nephropathy. Nephrol tivation in immunoglobulin A nephropathy. 96. Narendra U, Pauer GJ, Hagstrom SA: Genetic Dial Transplant 28: 282–288, 2013 Am J Med Sci 356: 114–120, 2018 analysis of complement factor H related 5, 71. Malik TH, Lavin PJ, Goicoechea de Jorge E, 85. Shi B, Wang L, Mou S, Zhang M, Wang Q, Qi CFHR5, in patients with age-related macular Vernon KA, Rose KL, Patel MP, et al.: A hybrid C, et al.: Identification of mannose-binding degeneration. Mol Vis 15: 731–736, 2009 CFHR3-1 gene causes familial C3 glomerul- lectin as a mechanism in progressive im- 97. Dasari S, Alexander MP, Vrana JA, Theis JD, opathy. J Am Soc Nephrol 23: 1155–1160, munoglobulin A nephropathy. Int J Clin Exp Mills JR, Negron V, et al.: DnaJ heat shock 2012 Pathol 8: 1889–1899, 2015 protein family B member 9 is a novel bio- 72. Medjeral-Thomas N, Malik TH, Patel MP, 86. Merinero HM, García SP, García-Fernández marker for fibrillary GN. J Am Soc Nephrol Toth T, Cook HT, Tomson C, et al.: A novel J, Arjona E, Tortajada A, Rodríguez de 29: 51–56, 2018 CFHR5 fusion protein causes C3 glomerul- Córdoba S: Complete functional charac- 98. Sethi S, Zand L, De Vriese AS, Specks U, opathy in a family without Cypriot ancestry. terization of disease-associated genetic Vrana JA, Kanwar S, et al.: Complement Kidney Int 85: 933–937, 2014 variants in the complement factor H gene. activation in pauci-immune necrotizing and 73. Xiao X, Ghossein C, Tortajada A, Zhang Y, Kidney Int 93: 470–481, 2018 crescentic glomerulonephritis: Results of a Meyer N, Jones M, et al.: Familial C3 glomer- 87. Medjeral-Thomas NR, Lomax-Browne HJ, proteomic analysis. Nephrol Dial Transplant ulonephritis caused by a novel CFHR5-CFHR2 Beckwith H, Willicombe M, McLean AG, 32[Suppl 1]: i139–i145, 2017 fusion gene. Mol Immunol 77: 89–96, 2016 Brookes P, et al.: Circulating complement 99. Zhao J, Wu H, Khosravi M, Cui H, Qian X, 74. Wong EKS, Kavanagh D: Diseases of com- factor H-related proteins 1 and 5 correlate Kelly JA, et al.BIOLUPUS Network; GENLES plement dysregulation-an overview. Semin with disease activity in IgA nephropathy. Network;: Association of genetic variants in Immunopathol 40: 49–64, 2018 Kidney Int 92: 942–952, 2017 complement factor H and factor H-related 75. Medjeral-Thomas NR, O’Shaughnessy MM, 88. Thurman JM, Laskowski J: Complement genes with systemic lupus erythematosus O’Regan JA, Traynor C, Flanagan M, Wong factor H-related proteins in IgA nephropathy- susceptibility. PLoS Genet 7: e1002079, 2011 L, et al.: C3 glomerulopathy: Clinicopatho- sometimes a gentle nudge does the trick. 100. Davila S, Wright VJ, Khor CC, Sim KS, logic features and predictors of outcome. Kidney Int 92: 790–793, 2017 Binder A, Breunis WB, et al.International Clin J Am Soc Nephrol 9: 46–53, 2014 89. Jullien P, Laurent B, Claisse G, Masson I, Meningococcal Genetics Consortium;: 76. Rauen T, Eitner F, Fitzner C, Sommerer C, Dinic M, Thibaudin D, et al.: Deletion vari- Genome-wide association study identifies Zeier M, Otte B, et al.STOP-IgAN Investi- ants of CFHR1 and CFHR3 associate with variants in the CFH region associated with gators;: Intensive Supportive care plus im- mesangial immune deposits but not with host susceptibility to meningococcal disease. munosuppression in IgA nephropathy. progression of IgA nephropathy. JAmSoc Nat Genet 42: 772–776, 2010 NEnglJMed373: 2225–2236, 2015 Nephrol 29: 661–669, 2018 101. Hughes AE, Orr N, Esfandiary H, Diaz-Torres 77. Kiryluk K, Li Y, Scolari F, Sanna-Cherchi S, 90. Zhai YL, Meng SJ, Zhu L, Shi SF, Wang SX, M, Goodship T, Chakravarthy U: A common Choi M, Verbitsky M, et al.: Discovery of Liu LJ, et al.: Rare variants in the complement CFH haplotype, with deletion of CFHR1 and new risk loci for IgA nephropathy implicates Factor H-related protein 5 gene contribute to CFHR3, is associated with lower risk of age- genes involved in immunity against intestinal genetic susceptibility to IgA nephropathy. related macular degeneration. Nat Genet pathogens. Nat Genet 46: 1187–1196, 2014 J Am Soc Nephrol 27: 2894–2905, 2016 38: 1173–1177, 2006 78. Kiryluk K, Novak J: The genetics and im- 91. Tortajada A, Gutiérrez E, Goicoechea de 102. Edwards AO, Ritter R 3rd, Abel KJ, Manning munobiology of IgA nephropathy. JClin Jorge E, Anter J, Segarra A, Espinosa M, A, Panhuysen C, Farrer LA: Complement Invest 124: 2325–2332, 2014 et al.: Elevated factor H-related protein 1 factor H polymorphism and age-related 79. Groopman EE, Rasouly HM, Gharavi AG: and factor H pathogenic variants decrease macular degeneration. Science 308: 421–424, Genomic medicine for kidney disease. Nat complement regulation in IgA nephropa- 2005 Rev Nephrol 14: 83–104, 2018 thy. Kidney Int 92: 953–963, 2017 103. Holmes LV, Strain L, Staniforth SJ, Moore I, 80. Zhu L, Zhai YL, Wang FM, Hou P, Lv JC, Xu 92. Monteferrante G, Brioschi S, Caprioli J, Marchbank K, Kavanagh D, et al.: De- DM,etal.:VariantsincomplementfactorH Pianetti G, Bettinaglio P, Bresin E, et al.: termining the population frequency of the and complement factor H-related protein Genetic analysis of the complement factor CFHR3/CFHR1 deletion at 1q32. PLoS One genes, CFHR3 and CFHR1, affect comple- H related 5 gene in haemolytic uraemic 8: e60352, 2013 ment activation in IgA nephropathy. JAm syndrome. Mol Immunol 44: 1704–1708, 104. Zipfel PF, Mache C, Müller D, Licht C, Soc Nephrol 26: 1195–1204, 2015 2007 Wigger M, Skerka C; European DEAP-HUS 81. Zhu L, Guo WY, Shi SF, Liu LJ, Lv JC, 93. Westra D, Vernon KA, Volokhina EB, Study Group: DEAP-HUS: Deficiency of CFHR Medjeral-Thomas NR, et al.: Circulating PickeringMC,vandeKarNC,vanden plasma proteins and autoantibody-positive complement factor H-related protein 5 Heuvel LP: Atypical hemolytic uremic syn- form of hemolytic uremic syndrome. Pe- levels contribute to development and pro- drome and genetic aberrations in the com- diatr Nephrol 25: 2009–2019, 2010 gression of IgA nephropathy. Kidney Int 94: plement factor H-related 5 gene. JHum 105. Heinen S, Sanchez-Corral P, Jackson MS, 150–158, 2018 Genet 57: 459–464, 2012 Strain L, Goodship JA, Kemp EJ, et al.: De 82. Xie J, Kiryluk K, Li Y, Mladkova N, Zhu L, Hou 94. Abrera-Abeleda MA, Nishimura C, Smith novo gene conversion in the RCA gene P, et al.: Fine mapping implicates a deletion JL, Sethi S, McRae JL, Murphy BF, et al.: cluster (1q32) causes mutations in complement of CFHR1 and CFHR3 in protection from IgA Variations in the complement regulatory factor H associated with atypical hemolytic nephropathy in Han Chinese. JAmSoc genes factor H (CFH) and factor H related 5 uremic syndrome. Hum Mutat 27: 292–293, Nephrol 27: 3187–3194, 2016 (CFHR5) are associated with membranoprolifer- 2006 83. Jia M, Zhu L, Zhai YL, Chen P, Xu BY, Guo ative glomerulonephritis type II (dense deposit 106. Pangburn MK, Rawal N, Cortes C, Alam WY, et al.: Variation in complement factor H disease). J Med Genet 43: 582–589, 2006 MN, Ferreira VP, Atkinson MA: Polyanion- affects complement activation in immuno- 95. Vernon KA, Goicoechea de Jorge E, Hall AE, induced self-association of complement globulin A vasculitis with nephritis [published Fremeaux-Bacchi V, Aitman TJ, Cook HT, factor H. JImmunol182: 1061–1068, 2009

JASN 31: 241–256, 2020 CFHR genes in kidney diseases 255 REVIEW www.jasn.org

107. Manuelian T, Hellwage J, Meri S, Caprioli J, to factor H and factor H-related proteins. potential. J Am Soc Nephrol 29: 1141–1153, Noris M, Heinen S, et al.: Mutations in factor Biochem J 331: 41–47, 1998 2018 H reduce binding affinity to C3b and heparin 112. DiScipio RG: Ultrastructures and interac- 117. Yang Y, Denton H, Davies OR, Smith- and surface attachment to endothelial cells tions of complement factors H and I. Jackson K, Kerr H, Herbert AP, et al.: An in hemolytic uremic syndrome. J Clin Invest J Immunol 149: 2592–2599, 1992 engineered complement Factor H construct 111: 1181–1190, 2003 113. Pouw RB, Gómez Delgado I, López Lera A, for treatment of C3 Glomerulopathy. JAm 108. Zhang P, Zhu M, Geng-Spyropoulos M, Rodríguez de Córdoba S, Wouters D, Soc Nephrol 29: 1649–1661, 2018 Shardell M, Gonzalez-Freire M, Gudnason Kuijpers TW, et al.: High complement Factor 118. Park CT, Wright SD: Fibrinogen is a compo- V, et al.: A novel, multiplexed targeted mass H-related (fhr)-3 levels are associated with nent of a novel lipoprotein particle: Factor spectrometry assay for quantification of the atypical hemolytic-uremic syndrome- H-related protein (FHRP)-associated lipo- complement factor H (CFH) variants and risk allele cfhr3*b. Front Immunol 9: 848, protein particle (FALP). Blood 95: 198–204, CFH-related proteins 1-5 in human plasma. 2018 2000 Proteomics 17: 6, 2017 114. Blaum BS, Hannan JP, Herbert AP, 119. Park CT, Wright SD: Plasma lipopolysaccharide- 109. van Beek AE, Kamp A, Kruithof S, Kavanagh D, Uhrín D, Stehle T: Structural binding protein is found associated with a Nieuwenhuys EJ, Wouters D, Jongerius I, basis for sialic acid-mediated self-recognition particle containing apolipoprotein A-I, phos- et al.: Reference intervals of factor H and by complement factor H. Nat Chem Biol 11: pholipid, and factor H-related proteins. JBiol factor H-related proteins in healthy Children. 77–82, 2015 Chem 271: 18054–18060, 1996 Front Immunol 9: 1727, 2018 115. Goicoechea de Jorge E, Caesar JJ, Malik 120. ClinicalTrials.gov. Available at: https:// 110. Schäfer N, Grosche A, Reinders J, Hauck TH, Patel M, Colledge M, Johnson S, et al.: clinicaltrials.gov/ct2/home. Accessed August SM, Pouw RB, Kuijpers TW, et al.: Comple- Dimerization of complement factor H-related 15, 2019 ment regulator FHR-3 is elevated either locally proteins modulates complement activation in 121. Nester CM, Smith RJ: Complement inhibition or systemically in a selection of autoimmune vivo. Proc Natl Acad Sci U S A 110: 4685–4690, in C3 glomerulopathy. Semin Immunol 28: diseases. Front Immunol 7: 542, 2016 2013 241–249, 2016 111. Prodinger WM, Hellwage J, Spruth M, 116. Michelfelder S, Fischer F, Wäldin A, Hörle 122. Zipfel PF, Wiech T, Rudnick R, Afonso S, Dierich MP, Zipfel PF: The C-terminus of KV, Pohl M, Parsons J, et al.: The MFHR1 Person F, Skerka C: Complement inhibitors factor H: Monoclonal antibodies inhibit hep- fusion protein is a novel synthetic multitarget in clinical trials for glomerular diseases. arin binding and identify epitopes common complement inhibitor with therapeutic Front Immunol 10: 2166, 2019

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Supplemental TOC

Supplementary Table I: Morphological Differences in atypical Hemolytic Uremic Syndrome (aHUS) and C3 Glomerulopathy Supplementary Table II: Alterations in the Factor H-CFHR gene cluster in aHUS/dEAP-HUS and C3 glomerulopathy

Supplementary Table I: Morphological Differences in atypical Hemolytic Uremic Syndrome (aHUS) and C3 Glomerulopathy

Disease Complement Morphologic Active phase Chronic phase activation pattern aHUS Strong, cell TMA Endothelial and Formation of new surface mesangial cell lysis, extracellular matrix thrombus formation at the GBM C3 Glomerulopathy Moderate, fluid MPGN / DDD Mesangial cell New extracellular phase and cell proliferation, matrix at the GBM surface inflammatory cell and mesangium influx

TMA = thrombotic microangiopathy, MPGN = membranoproliferative glomerulonephritis, DDD = dense deposit disease, GBM = glomerular basement membrane.