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Adam MP, Bick S, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2025.
Bertha Martín, PhD andRichard JH Smith, MD.
Author Information and AffiliationsInitial Posting:July 20, 2007; Last Update:April 5, 2018.
Estimated reading time: 44 minutes
C3 glomerulopathy (C3G) is a complex ultra-rare complement-mediated renal disease caused by uncontrolled activation of the complement alternative pathway (AP) in the fluid phase (as opposed to cell surface) that is rarely inherited in a simple mendelian fashion. C3G affects individuals of all ages, with a median age at diagnosis of 23 years. Individuals with C3G typically present with hematuria, proteinuria, hematuria and proteinuria, acute nephritic syndrome or nephrotic syndrome, and low levels of the complement component C3. Spontaneous remission of C3G is uncommon, and about half of affected individuals develop end-stage renal disease (ESRD) within ten years of diagnosis, occasionally developing the late comorbidity of impaired visual acuity.
The definitive diagnosis of C3G requires a renal biopsy with specialized immunofluorescence and electron microscopy studies both for diagnosis and to distinguish between the two major subtypes of C3G: C3 glomerulonephritis (C3GN) and dense deposit disease (DDD). Some individuals will havebiallelic orheterozygous pathogenic variants identified bymolecular genetic testing in one or more of the genes that have been implicated in the pathogenesis of C3G (i.e.,C3,CD46,CFB,CFH,CFHR1,CFHR5,CFI, andDGKE).
Treatment of manifestations: Nonspecific therapies used to treat numerous chronic glomerular diseases, including angiotensin-converting enzyme inhibitors, angiotensin II type-1 receptor blockers, and lipid-lowering agents (in particular hydroxymethylglutaryl coenzyme A reductase inhibitors). Complement inhibition with a terminal pathway blocker may alter disease course in some individuals. When ESRD develops, treatment options are limited to dialysis or transplantation. C3G recurs in nearly all grafts and is the predominant cause of graft failure in 50%-90% of transplant recipients.
Prevention of primary manifestations: Plasma replacement therapy in individuals with pathogenic variants inCFH may be effective in controlling complement activation and slowing progression of ESRD.
Surveillance: Close monitoring of renal function by a nephrologist with familiarity with the C3G disease spectrum, complete biannual assessment of the complement pathway, periodic eye examinations to evaluate the fundus.
Evaluation of relatives at risk: If the family history is positive for renal disease, evaluation of apparently asymptomatic at-risk relatives can includemolecular genetic testing (if the pathogenic variants in the family are known), urinalysis, and comprehensive analysis of the complement system.
C3G is a complex genetic disorder that is rarely inherited in a simple mendelian fashion. Multiple affected persons within a single nuclear family are reported only occasionally, with both dominant and recessive inheritance being described.
C3 glomerulopathy (C3G) is a complex ultra-rare complement-mediated renal disease caused by uncontrolled activation of the complement alternative pathway (AP) in the fluid phase (as opposed to cell surface); it is rarely inherited in a simple mendelian fashion.
C3Gshould be suspected in individuals of all ages who present with one of the following:
The diagnosis of C3Gis established in aproband with typical findings onrenal biopsy. Some individuals will havebiallelic orheterozygous pathogenic variants identified bymolecular genetic testing in one or more of the genes listed inTable 1.
Note: Identification of apathogenic variant may help to direct treatment of the individual.
Renal biopsy. The definitive diagnosis of C3G requires a renal biopsy with specialized studies (seeFigure 1) both for diagnosis and to distinguish between C3 glomerulonephritis (C3GN) and dense deposit disease (DDD).
Note: Timing of the biopsy is important. If the presentation suggests post-infectious glomerulonephritis (PIGN; seeFigure 2), waiting for three months is typically recommended. During that interval, the hypocomplementemia, hematuria, and proteinuria that are characteristic of both PIGN and C3G should resolve in cases of PIGN [Walker et al 2007,Nester & Smith 2016,Goodship et al 2017].
Molecular genetic testing approaches can include amultigene panel,more comprehensivegenomic testing, andserial single-gene testing:
Molecular Genetic Testing Used in C3G
| Gene 1, 2 | Proportion of C3G Attributed to Pathogenic Variants in Gene | Proportion of Pathogenic Variants 3 Detectable by Method | |
|---|---|---|---|
| Sequence analysis 4 | Gene-targeteddeletion/duplication analysis 5 | ||
| C3 | ~11% 6 | ~100% | Unknown |
| CD46 | 0%~2% 7 | 100% | Unknown |
| CFB | <1% 8 | 100% | Unknown |
| CFH | ~12% 9 | ~98% | ~2% |
| CFHR1 duplication 10 | 2 individuals | NA | 100% 11 |
| CFHR1/CFHR5 hybridallele 10 | 3 individuals | NA | 100% 12 |
| CFHR3/CFHR1 hybridallele 10 | 5 individuals | NA | 100% 13 |
| CFHR5 | See footnote 14. | See footnote 15. | Unknown (general population); 100% (Cyprus) 14 |
| CFHR5/CFHR2 hybridallele 10 | 2 individuals | NA | 100% 16 |
| CFI | ~5% 17 | 100% | Unknown |
| DGKΕ | 13 individuals 18 | ~100% | Unknown |
Genes are listed in alphabetic order.
SeeTable A. Genes and Databases forchromosomelocus and protein.
SeeMolecular Genetics for information on allelic variants detected in thisgene.
Sequence analysis detects variants that are benign,likely benign, ofuncertain significance,likely pathogenic, or pathogenic. Variants may include small intragenic deletions/insertions andmissense,nonsense, andsplice site variants; typically,exon or whole-gene deletions/duplications are not detected. For issues to consider in interpretation ofsequence analysis results, clickhere.
Gene-targeteddeletion/duplication analysis detects intragenic deletions or duplications. Methods used may include a range of techniques such asquantitative PCR, long-range PCR, multiplex ligation-dependent probe amplification (MLPA), and agene-targeted microarray designed to detect single-exon deletions or duplications.
CFHR hybrid alleles are thegene fusion products ofnonallelic homologous recombination between the highly homologousCFHR genes [Gale et al 2010,Malik et al 2012,Tortajada et al 2013,Chen et al 2014,Medjeral-Thomas et al 2014,Xiao et al 2016,Togarsimalemath et al 2017] (for details ofexon arrangements seeFigure 3).
Four individuals of non-Cypriot origin; however, hundreds of affected individuals with aduplication of exons 2 and 3, presumably due to afounder effect, have been identified in Cyprus [Gale et al 2010,Athanasiou et al 2011,Deltas et al 2013].
Three patients of non-Cypriot origin have been reported with variants detectable by sequencing [Sethi et al 2012a,Vernon et al 2012,Besbas et al 2014].
SeeFigure 3.

Complement factor H-related hybrid proteins and C3G Adapted from Togarsimalemath et al [2017] and references therein
Age of onset. C3 glomerulopathy (C3G) affects individuals of all ages.Lu et al [2012] report a 1:1 female:male distribution and a median age at diagnosis of 23 years.
In comparing the two major subtypes, the median age at time of diagnosis in C3 glomerulonephritis (C3GN) is higher than in dense deposit disease (DDD). In childhood, DDD is more frequently diagnosed than C3GN [Nester & Smith 2016,Riedl et al 2017].
Renal disease. Individuals with C3G typically present with one of the following findings:
Hypocomplementemia. Individuals with C3G have low levels of complement component C3. Complement dysregulation can be mediated by autoantibodies (seePathophysiology).
Autoantibodies that may be detected in individuals with C3G:
Course and progression
Acquired partial lipodystrophy (APL). APL may develop as a direct aftermath of complement activation in 5%-17% of persons with C3G [Barbour et al 2013b,Goodship et al 2017]. The association between APL and C3G is related to the effects of AP dysregulation on both kidneys and adipose tissue [Goodship et al 2017]. The deposition of activated complement components in adipose tissue destroys adipocytes in areas where factor D (fD, also known as adipsin) is high; loss of subcutaneous fat in the upper half of the body typically precedes the onset of kidney disease by several years.
Eye findings. Individuals with C3G develop drusen as a result of complement activation, often in early adulthood [Barbour et al 2013b,Thomas et al 2014,Goodship et al 2017]. The whitish-yellow deposits, which lie within Bruch's membrane beneath the retinal pigment epithelium of the retina, are similar in composition and structure to the deposits observed in the kidney [D'Souza et al 2009,Lu et al 2012,Barbour et al 2013b]. The retinal distribution of drusen is variable [Thomas et al 2014,Goodship et al 2017] and initially has little impact on visual acuity or visual fields. However, vision loss can occur later in life [Cebeci et al 2016].
Recent investigations convey the importance of the complications that result from drusen [Cebeci et al 2016,Dalvin et al 2016,Savige et al 2016]. Tests of retinal function such as dark adaptation, electroretinography, and electrooculography can gradually become abnormal, and vision can deteriorate as subretinal neovascular membranes, macular detachment, and central serous retinopathy develop [Cebeci et al 2016,Dalvin et al 2016,Savige et al 2016].
The long-term risk for visual problems in individuals with C3G is approximately 10%. No correlation exists between disease severity in the kidney and in the eye.
SeeFigure 4. Fluid-phase dysregulation of the alternate pathway (AP) of the complement cascade is the triggering pathophysiologic event in C3G, and dysregulation of the C3 convertase alone is necessary and sufficient to result in C3G [Martínez-Barricarte et al 2010,Paixão-Cavalcante et al 2012,Zhang et al 2012].

Complement alternative pathway (AP) Left. Three phases of complement activity are illustrated:
During disease progression, activation of downstream complement proteins in the solid phase, in particular cleavage of C5 to C5a and C5b, can contribute to tissue injury in the micro-environment of the renal glomerulus [Appel et al 2005,Smith et al 2007]. Current consensus considers that in C3G, uncontrolled regulation of the AP may be due to both genetic and/or acquired drivers of disease [Servais et al 2012,Nester & Smith 2016,Goodship et al 2017].
Acquired drivers of disease include autoantibodies such as C3 nephritic factors (C3NeFs), C4 nephritic factors (C4NeFs), C5 nephritic factors (C5NeFs), factor H autoantibodies (FHAA), and factor B autoantibodies (FBAA).
C3NeFs and C5NeFs are most commonly detected and are autoantibodies that recognize neoantigenic epitopes on C3bBb, the C3 convertase of the AP, and on C3bBbC3b, the C5 convertase of the terminal pathway, respectively (seeFigure 4) [Paixão-Cavalcante et al 2012,Zhang et al 2012,Nester & Smith 2013a,Nicolas et al 2014]. C3 convertases cleave C3 into C3b and C3a, while C5 convertases cleave C5 into C5a and C5b. In the presence of C3NeFs and C5NeFs, the half-lives of C3 convertase and C5 convertase are increased. Persistent cleavage of C3 drives down serum concentrations of C3 and increases serum concentrations of its cleavage products, C3c and C3d, while persistent cleavage of C5 increases serum concentrations of soluble C5b-9. C4NeFs are found in fewer than 5% of individuals with C3GN and stabilize the C3 convertase of the classic and lectin pathways (C4b2a) [Zhang et al 2017].
Nephritic factors may persist in serum throughout the disease course [Schwertz et al 2001,Paixão-Cavalcante et al 2012,Zhang et al 2012]. Serum concentrations of C3NeFs can vary over time [Appel et al 2005,Paixão-Cavalcante et al 2012,Zhang et al 2012,Servais et al 2013,Rabasco et al 2015]. Their presence is nearly always associated with evidence of complement activation such as decrease in serum concentration of C3 and increase in serum concentration of C3 cleavage products (e.g., C3c and C3d), but the relationship between nephritic factors, C3, and prognosis is not clear [Paixão-Cavalcante et al 2012,Zhang et al 2012,Rabasco et al 2015]. The observed differences may be reconciled by several observations relevant to C3NeFs, which have been most thoroughly studied. First, not all C3NeFs recognize the same epitope on C3bBb; second, the methods for their detection vary; third, many studies do not report titers; and fourth, there is good evidence that the triggering epitopes can change over time [Ohi et al 1992,Spitzer & Stitzel 1996,Paixão-Cavalcante et al 2012,Zhang et al 2012].
The consequence of AP dysregulation in C3G is kidney damage. As the degree of chronic damage increases, renal outcome ultimately becomes independent of the degree of complement dysregulation. With sufficient chronic damage, even if complement normalcy is restored, the likelihood of improving or stabilizing renal function becomes remote and ESRD ensues.
Factor H autoantibodies (FHAA) have been reported in individuals with C3G; epitope mapping shows that these autoantibodies bind the N-terminus of fH [Zhang et al 2012,Blanc et al 2015,Goodship et al 2017].
Factor B autoantibodies (FBAA) have been linked to C3G; however, their role in disease remains unclear [Pickering et al 2013]. FBAAs were identified in a person with DDD without serum C3NeFs. FBAAs bind to and stabilize C3 convertase, targeting both fB and C3b, enhancing the consumption of C3. C5 convertase formation from C3 convertase is prevented, thus interfering with activation of the terminal complement cascade [Strobel et al 2010]. Additional studies have identified FBAAs targeting fB and C3b in two individuals with DDD; C3 convertase activity was increased although no C3NeFs were identified [Chen et al 2011].
As a general rule, C3Nefs, FHAAs, and FBAAs extend the half-life and stabilize C3 convertase, which leads to persistent AP activation in the fluid phase [Noris & Remuzzi 2015].
To date, the most strikinggenotype-phenotype correlation has been withCFHR fusion genes and the C3GN phenotype (as opposed to the DDD phenotype) (seeFigure 3).
C3 glomerulonephritis (C3GN) and dense deposit disease (DDD). Prior to adopting the C3G classification [Pickering et al 2013], dense deposit disease (DDD) was also described as membranoproliferative glomerulonephritis type 2 (MPGN2). C3 glomerulonephritis (C3GN) was recognized as atypical MPGN1 (Burkholder variant of MPGN1) and atypical MPGN3 (Strife and Anders variant of MPGN3) [D'Agati & Bomback 2012,Sethi et al 2016].
The rarity of C3G makes it difficult to estimate prevalence, although from epidemiologic studies, its prevalence in the USA is estimated at 2-3 per 1,000,000 [Smith et al 2007].
Table 2 includes other phenotypes caused by pathogenic variants in thegene(s) associated with C3G.
Allelic Disorders
| Gene | Phenotype 1 |
|---|---|
| CD46 | Atypical hemolytic-uremic syndrome |
| CFB | Atypical hemolytic-uremic syndrome |
| CFH | Factor H deficiency (OMIM609814);atypical hemolytic-uremic syndrome; basal laminar drusen (OMIM126700) |
| CFHR1 | Atypical hemolytic uremic syndrome |
| CFHR5 | CFHR5 deficiency (OMIM614809) |
| CFI | Factor I deficiency (OMIM610984);atypical hemolytic-uremic syndrome; age-related macular degeneration (OMIM615439) |
| DGKΕ | Nephrotic syndrome type 7 (OMIM615008);atypical hemolytic-uremic syndrome |
See hyperlinkedGeneReview or OMIMphenotype entry for more information.
Disorders to Consider in the Differential Diagnosis of C3G
| Disorder | Gene(s) | MOI | Clinical Features of This Disorder | |
|---|---|---|---|---|
| Overlapping w/C3G | Distinguishing from C3G | |||
| Post-infectious glomerulonephritis 1 | NA | Acquired | Hematuria, proteinuria, nephritic syndrome, edema, ↓ serum C3, C3 glomerular deposition, subepithelial hump-like deposits | Post-infection (throat or skin) often due to Group A hemolyticstreptococcus bacterium; ↓ levels of C3 resolve w/in 3 mos; glomerular codeposition of C3 & IgG |
| Immune-complex MPGN 2 | NA | Acquired | Hematuria, proteinuria, C3 deposits, subendothelial & subepithelial deposits, progressive disease | Immune complex-mediated, often low complement C4 levels; codeposition of C3 & IgG/IgM/C1q/C4 on IF |
| Juvenile acute non-proliferative glomerulonephritis 3 | NA | Acquired | Mesangial cell proliferation, subepithelial deposits on EM | C3 levels typically remaining in lower limits of nl |
| Familial lecithin-cholesterol acyltransferase deficiency 4 | LCAT | AR | ESRD, glomerular pattern of IF similar to dense deposit disease | Abnl lipoprotein (lipoprotein X); corneal opacities; normochromic anemia; capillary endothelial damage; cross-striated & vacuole structures |
| Partial lipodystrophy 5 | Several genes | AD/AR | Loss of subcutaneous fat in upper half of the body | No renal disease; no dysregulation of complement alternative pathway |
| Age-related macular degeneration 6 | Many genes | AD | Drusen | No renal disease |
| Malattia Leventinese & Doyne honeycomb retinal dystrophy 7 | EFEMP1 | AD | Drusen | No renal disease |
abnl = abnormal; AD =autosomal dominant; AR =autosomal recessive; EM = electron microscopy; IF = immunofluorescence; MOI =mode of inheritance; MPGN = membranoproliferative glomerulonephritis; nl = normal
To establish the extent of disease and needs in an individual diagnosed with C3G, the following evaluations are recommended if they have not already been completed:
Currently, there are no therapeutic agents specifically designed to target the underlying complement dysregulation that occurs in individuals with C3G. Nonspecific therapies are most commonly used.
Nonspecific therapies have been shown to be effective in numerous chronic glomerular diseases. The judicious use of these agents along with optimal blood pressure control is of benefit in individuals with C3G.
Renal allografts. When end-stage renal disease (ESRD) develops, treatment options are limited to dialysis or transplantation. When an individual with C3G elects to undergo a renal transplant, it is important to recognize that C3G recurs in nearly all grafts and is the predominant cause of graft failure in 50%-90% of transplant recipients [Appel et al 2005,Angelo et al 2011,Lu et al 2012,Servais et al 2012,Zand et al 2014,Salvadori & Bertoni 2016,Goodship et al 2017]. Data suggesting that any therapeutic interventions reverse this course are limited, although isolated reports have described the use of plasmapheresis, which appears to be of equivocal benefit [Fremeaux-Bacchi et al 1994,Kurtz & Schlueter 2002]. A thorough complement and genetic evaluation of the transplant recipient is recommended pre-transplantation as results may inform post-transplant care. In addition, a genetic assessment is recommended for relatives being considered as kidney donors.
Most treatments for C3G are ineffective; however, plasma replacement therapy in individuals with pathogenic variants inCFH has been reported by some authors to be effective in controlling complement activation and slowing progression of ESRD [Licht et al 2006]. Other authors report that the benefit of plasma exchange is inconsistent in reducing progression to ESRD [Kurtz & Schlueter 2002,McCaughan et al 2012,Servais et al 2013,Thomas et al 2014].
The following are appropriate:
There are very fewfamilial cases of C3G. However, if the family history is positive for renal disease, it is appropriate to evaluate apparently asymptomatic sibs of aproband and at-risk relatives to identify those who would benefit from periodic observation and continued follow up for management of renal disease.
Evaluations can include:
SeeGenetic Counseling for issues related to testing of at-risk relatives forgenetic counseling purposes.
Chronic kidney disease does not preclude pregnancy, but any pregnancy in a woman with C3G should be followed by a nephrologist and obstetrician with expertise in caring for pregnant women with chronic kidney disease [Nava et al 2017,Piccoli et al 2018].
SeeMotherToBaby for further information on medication use during pregnancy.
Numerous anti-complement therapies are entering clinical trials for individuals with C3G. These trials are registered underClinicalTrials.gov.
SearchClinicalTrials.gov in the US andEU Clinical Trials Register in Europe for access to information on clinical studies for a wide range of diseases and conditions.
Genetic counseling is the process of providing individuals and families withinformation on the nature, mode(s) of inheritance, and implications of genetic disorders to help themmake informed medical and personal decisions. The following section deals with geneticrisk assessment and the use of family history and genetic testing to clarify geneticstatus for family members; it is not meant to address all personal, cultural, orethical issues that may arise or to substitute for consultation with a geneticsprofessional. —ED.
C3G is a complex genetic disorder that is rarely inherited in a simple mendelian fashion. In most persons with C3G, inheritance is complex and incompletely understood. For these reasons,recurrence risk to family members is not known but likely very low.
Parents of aproband
Sibs of aproband
Offspring of aproband. The offspring of an individual withautosomal recessive C3G are obligate heterozygotes (carriers) for apathogenic variant.
Other family members. Each sib of theproband's parents is at a 50% risk of being acarrier of apathogenic variant.
Carrier testing for at-risk relatives requires prior identification of the pathogenic variants in the family.
Parents of aproband
Sibs of aproband
Offspring of aproband. Each child of an individual withautosomal dominant C3G has a 50% chance of inheriting thepathogenic variant; however,penetrance is extremely variable [Xiao et al 2014].
Other family members. The risk to other family members depends on the status of theproband's parents: if a parent has thepathogenic variant, his or her family members may be at risk.
Parents, sibs, and offspring of aproband. The risk to the family members of a proband who does not have identified pathogenic variants or a family history consistent withautosomal recessive or dominant inheritance is low.
See Management,Evaluation of Relatives at Risk for information on evaluating at-risk relatives for the purpose of early diagnosis and treatment.
Other autoimmune diseases, in particular diabetes mellitus type 1 andceliac disease, are diagnosed more frequently in families with C3G (16% of families) than would be expected based on estimates in the general population [Smith et al 2007,Lu et al 2012,Barbour et al 2013a,Thomas et al 2014].
Family planning
DNA banking. Because it is likely that testing methodology and our understanding of genes, pathogenic mechanisms, and diseases will improve in the future, consideration should be given to banking DNA from probands in whom a molecular diagnosis has not been confirmed (i.e., the causative pathogenic mechanism is unknown).
Once the pathogenic variants have been identified in an affected family member,prenatal testing for a pregnancy at increased risk andpreimplantation genetic testing are possible.
Differences in perspective may exist among medical professionals and within families regarding the use ofprenatal testing. While most centers would consider use of prenatal testing to be a personal decision, discussion of these issues may be helpful.
GeneReviews staff has selected the following disease-specific and/or umbrellasupport organizations and/or registries for the benefit of individuals with this disorderand their families. GeneReviews is not responsible for the information provided by otherorganizations. For information on selection criteria, clickhere.
Information in the Molecular Genetics and OMIM tables may differ from that elsewhere in the GeneReview: tables may contain more recent information. —ED.
C3 Glomerulopathy: Genes and Databases
OMIM Entries for C3 Glomerulopathy (View All in OMIM)
| 120700 | COMPLEMENT COMPONENT 3; C3 |
| 120920 | CD46 ANTIGEN; CD46 |
| 134370 | COMPLEMENT FACTOR H; CFH |
| 134371 | COMPLEMENT FACTOR H-RELATED 1; CFHR1 |
| 138470 | COMPLEMENT FACTOR B; CFB |
| 217030 | COMPLEMENT FACTOR I; CFI |
| 601440 | DIACYLGLYCEROL KINASE, EPSILON, 64-KD; DGKE |
| 608593 | COMPLEMENT FACTOR H-RELATED 5; CFHR5 |
| 609814 | COMPLEMENT FACTOR H DEFICIENCY; CFHD |
| 610984 | COMPLEMENT FACTOR I DEFICIENCY; CFID |
| 613779 | COMPLEMENT COMPONENT 3 DEFICIENCY, AUTOSOMAL RECESSIVE; C3D |
| 615008 | NEPHROTIC SYNDROME, TYPE 7; NPHS7 |
The complement system, composed of the classic pathway and the alternate pathway, is a component of the immune system that enhances the function of antibodies and phagocytes. C3 glomerulopathy (C3G) is caused by uncontrolled activation of the complement alternative pathway.
With the exception ofDGKE, all the genes discussed in association with C3G encode proteins in the complement system. C3 and CFB are integral to complement activation and together form C3bBb, a C3 convertase that amplifies the initial complement response, and C3bBbC3b, a C5 convertase that cleaves C5 into C5a and C5b to trigger the terminal pathway. CD46, CFH, CFHR1, CFHR5, and CFI are complement regulators. The role ofDGKE in complement activation, although minimal, is believed to be essential in normal podocyte function.
Familial cases of C3G are uncommon and when identified are most often highly penetrantheterozygous copy number variants involving theCFHR1-5 genes (seeFigure 3),homozygous variants that lead toCFH deficiency, or heterozygousgain-of-function variants inC3. Common to all of these variants is an impact on the regulation of the AP in the fluid phase [Noris & Remuzzi 2017].
Since C3G is rarely inherited in a simple mendelian fashion, the study of rare variants and haplotypes associated with disease is important.
Several studies have shown that some common variants in complement genes are also associated with C3G and increase the odds ratio of developing disease [Abrera-Abeleda et al 2011,Kobayashi et al 2017]. While the identification of common variants that are C3G "risk alleles"cannot be used to direct clinical care, the identification of rare variants in complement genes does affect patient care, especially in the context of a comprehensive assessment of complement function, which includes plasma levels of complement proteins and their split products, assays for autoantibodies, and tests of overall complement activity. For more detailed information, seeOsborne et al [2018].
Gene structure.C3 comprises 41 exons that encode complement C3, which has a molecular weight of 176 kd. The mature protein forms a beta chain and an alpha chain. For a detailed summary ofgene and protein information, seeTable A.
Benign variants. SeveralC3 variants (some of which are common in the population) are associated with C3G and define an at-risk haplotype [Hageman et al 2005,Smith et al 2007,Fremeaux-Bacchi et al 2008,Abrera-Abeleda et al 2011,Iatropoulos et al 2016,Riedl et al 2017,Osborne et al 2018].
Pathogenic variants. Pathogenic variants and their location are shown inTable 4.
C3 Pathogenic Variants Discussed in ThisGeneReview
| DNA Nucleotide Change | Predicted Protein Change | Affected Domain | Reference Sequences |
|---|---|---|---|
| c.443G>A | p.Arg148Gln | C3β chain | NM_000064 NP_000055 |
| c.1855G>A | p.Val619Met | Linker | |
| c.3125G>A | p.Arg1042Gln | TED | |
| c.3908G>A | p.Arg1303His | CUBf | |
| c.3959G>A | p.Arg1320Gln | CUBf | |
| c.4552T>C | p.Cys1518Arg | C345C | |
| c.4873T>C | p.Asp1625His | C345C |
Variants listed in the table have been provided by the authors.GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen
Normalgene product.C3 encodes complement component C3, the central activating protein of the AP. This 1,663-amino-acid protein has 15 domains, including the anaphylatoxin (ANA), αNT, CUB (C1r/C1s, Uegf, Bmp1), C345C, thioester (TED), linker (LNK), and anchor domains and eight macroglobulin (MG) domains (seeFigure 5). C3 is mainly synthesized in the liver, and it is the central protein of the complement system. Spontaneous or proteolytic cleavage of C3 generates the anaphylatoxin C3a (inflammatory effector cells) and the C3b fragment that deposits on cell surfaces triggering the complement cascade activation.

Schematic representation of complement component C3 The structural organization of C3 contains eight macroglobulins, anaphylatoxin (ANA), αNT, CUB (C1r/C1s, Uegf, Bmp1), C345C, linker, and thioester (TED) domains.
Abnormalgene product. Most pathogenic variants listed inTable 4 affect proper cleavage of C3 protein by affecting recognition sites for the binding of CFH and CFI, two regulators of complement activation. Pathogenic variants may also produce reduced quantities of C3 protein (i.e., truncating variants or frameshifts that lead to premature stop variants) [Martínez-Barricarte et al 2010].
Gene structure.CD46 (cluster differentiation 46) has 14 exons that encode the 43.7-kd membrane cofactor protein (MCP).
Benign variants. Several variants inCD46 have been associated with C3G and define an at-risk haplotype [Servais et al 2007,Fang et al 2008,Servais et al 2012,Osborne et al 2018].
Normalgene product.CD46 encodes MCP, a complement regulatory protein of 392 amino acids that is highly expressed in the kidney. It is a transmembrane protein and a member of the regulators of complement activation (RCA), and has eight domains: four short consensus repeat (SCRs 1-4-sushi) domains, which contain ligand-binding domains for decay and cofactor activity; an O-linked-glycosylation site, rich in serine, threonine, and proline (STP)domain, which can be alternately spliced; a helical transmembrane domain; and two cytoplasmic topological domains. Its major role in controlling complement activity is to inactivate C3b and C4b by functioning as a cofactor for factor I [Servais et al 2012,Liszewski & Atkinson 2015].
Abnormalgene product. Pathogenic variants inCD46 typically lead to reduced surface expression of MCP, which contributes to defective surface regulation of complement [Servais et al 2012].
Gene structure.CFB comprises 18 exons that encode complement factor B, which has a molecular weight of 93 kd. For a detailed summary ofgene and protein information, seeTable A.
Benign variants. Benign variants inCFB associated with complement regulation have been described [Gold et al 2006].
Pathogenic variants. The p.Ser367Argpathogenic variant is in the von Willebrand factor A (VWFa)domain, the catalytic unit of Bb, and is again-of-function variant that contributes to AP dysregulation [Imamura et al 2015].
CFB Pathogenic Variants Discussed in ThisGeneReview
| DNA Nucleotide Change | Predicted Protein Change | Reference Sequences |
|---|---|---|
| c.1099A>C | p.Ser367Arg | NM_001710 NP_001701 |
Variants listed in the table have been provided by the authors.GeneReviews staff has not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen
Normalgene product.CFB is composed of 764 amino acids and has five domains: three complement component protein (sushi) domains; a VWFadomain; and a peptidase S1 (serine protease) domain. Factor B (fB) is a component of the AP. It binds to C3b and is then cleaved by fD into Ba, a non-catalytic fragment that is released, and Bb, a catalytic subunit that remains bound to C3b to form C3 convertase (C3bBb). The fB cleavage site is near the N-terminus of the VWFa domain.
Abnormalgene product. Pathogenic variants inCFB may lead togain-of-function properties that contribute to the dysregulation of the complement cascade [Alberts et al 2002,Imamura et al 2015].
Gene structure.CFH has 23 exons that encode complement factor H, a protein of 1,231 amino acids. For a detailed summary ofgene and protein information, seeTable A,Gene.
Benign variants. Several variants ofCFH (some of which are common in the population) define an at-risk haplotype that has been associated with C3G [Hageman et al 2005,Servais et al 2007,Smith et al 2007,Zhang et al 2012,Johnson et al 2014,Xiao et al 2014,Merinero et al 2018,Riedl et al 2017,Osborne et al 2018].
Pathogenic variants.CFH pathogenic variants in C3G occur inheterozygous,homozygous, andcompound heterozygous states.CFH has been implicated in C3G by the following:
CFH Pathogenic Variants Discussed in ThisGeneReview
| DNA Nucleotide Change (Alias 1) | Predicted Protein Change (Alias 1) | Reference Sequences |
|---|---|---|
| c.380G>T | p.Arg127Leu | NM_000186 NP_000177 |
| c.670_672delAAG | p.Lys224del (ΔLys224) | |
| c.1606T>C (1679T>C) | p.Cys536Arg (Cys518Arg) | |
| c.2655del | p.Arg885SerfsTer13 | |
| c.2876G>A (2949G>A) | p.Cys959Tyr (Cys991Tyr) |
Variants listed in the table have been provided by the authors.GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen
Variant designation that does not conform to current naming conventions
Normalgene product. Complement factor H (fH) protein is the key regulator of the alternative pathway of complement and is composed of 1,231 amino acids. Its structural organization is based on 20 homologous repeat domains (short consensus repeats [SCRs] or sushi domains). Each SCR has 60 amino acids. The first four SCRs (1-4) at the N-terminus are essential for fluid-phase complement regulation, binding of fH to C3b, decay acceleration activity of C3bBb, and fI cofactor activity in mediating the cleavage of C3b to iCb3. The last two SCRs (19-20) at the C terminus bind to cell surfaces to regulate C3 convertase in that microenvironment. SeeFigure 6.
Abnormalgene product.CFH pathogenic variants associated with C3G are more frequently found in the N-terminal short consensus repeats (SCRs 1-4), a region essential for fluid-phase complement control. In contrast, in atypical hemolytic uremic syndrome (aHUS), pathogenic variants are more frequently located in the carboxy terminus (SCRs 18-20), a region involved in cell surface regulation.
Gene structure.CFHR1 comprises six exons that encode complement factor H-related protein 1. For a detailed summary ofgene and protein information, seeTable A,Gene.
Pathogenic variants. Aduplication of exons 2 through 5 results in an abnormal fusion protein (Figure 3). The duplication alters the complex oligomerization of the FHR proteins, leading to increased FHR deregulation likely due to increased binding to C3b, iC3b, and C3dg, with decreased fH binding and decreased AP control (seeFigure 3) [Tortajada et al 2013].
CFHR1 Pathogenic Variants Discussed in ThisGeneReview
| DNA Nucleotide Change | Predicted Protein Change | Reference Sequences |
|---|---|---|
| Dup exons 1-4 | Duplication of all amino acids in SCR 1-4 of protein | NM_002113 NP_002104 |
Variants listed in the table have been provided by the authors.GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen
Normalgene product.CFHR1 encodes complement factor H-related 1 (FHR1), a protein of 330 amino acids and a member of the regulators of complement activation (RCA) family. Its structural organization is highly homologous to fH, although FHR1 has only five SCRs. The last two SCRs (SCRs 4 and 5) share 96%-100% homology to SCRs 19 and 20 of fH. FHR1 homodimerizes through its first two SCRs and also forms heterodimers with FHR2 and FHR5.
Abnormalgene product. Fusion proteins of FHR1 lead to the formation of complex multimers with FHR1, FHR2, and FHR5 that alter complement regulation by outcompeting fH, which results in reduced convertase regulation (seeFigure 3) [Xiao et al 2016].
Gene structure.CFHR5 has ten exons that encode complement factor H-related 5 (FHR5), a protein of 551 amino acids organized into nine SCRs. For a detailed summary ofgene and protein information, seeTable A,Gene.
Benign variants. SeveralCFHR5 variants (some of which are common in the population) are associated with C3G and define an at-risk haplotype [Abrera-Abeleda et al 2006,Zipfel et al 2015,Osborne et al 2018].
Pathogenic variants. Pathogenic variants are more frequently associated with C3GN than with DDD (CFHR5 nephropathy is a type of C3GN) [Goicoechea de Jorge et al 2009].
Normalgene product. The normal gene product encoded byCFHR5 is complement factor H-related protein 5 (FHR5), a plasma protein organized like fH in repetitive SCRs. FHR5 has nine SCRs and possesses fI-dependent cofactor activity that leads to inactivation of C3b [McRae et al 2001,Rodríguez de Córdoba et al 2004,McRae et al 2005]. In 92 renal biopsies from patients with different glomerular diseases, FHR5 was present in all complement-containing glomerular immune deposits [Murphy et al 2002], suggesting that FHR5 plays an important role in protecting the glomerulus from complement activation. The precise role of FHR5 in the physiopathology of C3G remains to be determined.
Abnormalgene product. Several abnormal gene products ofCFHR5 have been reported in association with C3G. These products usually arise as a consequence ofnonallelic homologous recombination, which results in hybrid gene formation (seeFigure 3).
The presence ofCFHR5 pathogenic variants in C3G is consistent with the hypothesis that FHRs play an important role in the complement regulation and disease pathogenesis [Abrera-Abeleda et al 2006,Zhang et al 2013].
Gene structure.CFI comprises 13 exons that encode complement factor I (fI), which has a molecular weight of 33 kd. For a detailed summary ofgene and protein information, seeTable A.
Benign variants. SeveralCFI variants (some of which are common in the population) are associated with C3G and define an at-risk haplotype [Fremeaux-Bacchi et al 2013,Imamura et al 2015,Chauvet et al 2017,Osborne et al 2018].
Pathogenic variants
CFI Pathogenic Variants Discussed in ThisGeneReview
| DNA Nucleotide Change | Predicted Protein Change (Alias 1) | Reference Sequences |
|---|---|---|
| c.719C>G | p.Ala240Gly (Ala222Gly) | NM_000204 NP_000195 |
| c.-4C>T | ||
| c.170G>A | p.Gly57Asp |
Variants listed in the table have been provided by the authors.GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen
Variant designation that does not conform to current naming conventions
Normalgene product.CFI encodes complement fI, a protein of 583 amino acids synthesized in the liver. The fI protein cleaves fluid-phase and cell-bound C3b and C4b, inhibiting their activity in the complement cascade. Factor H and several other RCA proteins are obligatory cofactors for fI activity.
Abnormalgene product. Abnormal fI may lead to a partial reduction in secreted fI, thus compromising its cofactor activity with fH [Servais et al 2012]. Deficiency in fI can lead to complement dysregulation and consequently low serum levels of other complement proteins.
Gene structure.DGKE comprises 11 exons that encode diacylglycerol kinase epsilon, which has a molecular weight of 64 kd. For a detailed summary ofgene and protein information, seeTable A.
Benign variants. SeveralDGKE variants (some of which are common in the population) are associated with C3G and define an at-risk haplotype [Osborne et al 2018].
Pathogenic variants. Severalloss-of-function variants have been associated with C3G including the following:
DGKE Pathogenic Variants Discussed in ThisGeneReview
| DNA Nucleotide Change | Predicted Protein Change | Reference Sequences |
|---|---|---|
| c.127C>T | p.Gln43Ter | NM_003647 NP_003638 |
| c.301A>T | p.Lys101Ter | |
| c.610delA | p.Thr204GlnfsTer6 | |
| c.966G>A | p.Trp322Ter | |
| c.1050G>A | p.Trp350Ter |
Note on variant classification: Variants listed in the table have been provided by the authors.GeneReviews staff have not independently verified the classification of variants.
Note on nomenclature:GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen
Normalgene product.DGKE is unrelated to the complement pathway.DGKE encodes diacylglycerol kinase epsilon (DGKE), a lipid kinase of 567 amino acids expressed in podocytes, glomerular capillary endothelial cells, and platelets. DGKE plays a key role in signal transduction by affecting the balance between diacylglycerol kinase and phosphatidic acid, thus controlling DAG levels within the cell [Lemaire et al 2013]. The role of DGKE in complement activation is minimal; however, it is believed to play an essential role in normal podocyte function [Ozaltin et al 2013].
In the kidney, DGKE is ubiquitously expressed in podocytes and endothelial cells. AlthoughDgkenull mice do not have spontaneous clinical signs of kidney disease and have normal serum creatinine and urinary albumin, they develop subclinical microscopic anomalies of the glomerular endothelium that worsen with age, as well as glomerular capillary occlusion when exposed to nephrotoxic serum [Zhu et al 2016].
Abnormalgene product. Abnormal DGKE may lead to prothrombosis through sustained signaling by arachidonic acid-containing diacylglycerol (AA-DAG) [Lemaire et al 2013].
Contact Information
Richard JH Smith
Division of Nephrology
University of Iowa
200 Hawkins Drive
Iowa City, IA 52242
Telephone: 319-356-3612
Fax: 319-356-4108
Email: richard-smith@uiowa.edu
Supported in part by grant RO1-DK110023 from the NIDDK (RJHS)
Johnny Cruz Corchado; University of Iowa (2011-2018)
Bertha Martín, PhD (2018-present)
Sanjeev Sethi, MD, PhD; Mayo Clinic (2007-2011)
Richard JH Smith, MD (2007-present)
Peter F Zipfel, PhD habil Prof; Hans Knöll Institute (2007-2011)
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