Skip to content
How It Works
Explore
Ask a Question Resources Pricing
Who It's For
Patients
Decode results, prep for appointments, weigh options.
Caregivers & advocates
Carry the research load for someone you love.
Providers & clinicians
Resources for patients in your practice.
Log In Sign Up
PubMed This is a summary of 21 peer-reviewed journal articles Updated
Nephrology

Biology and Subtypes: Genetic vs. Acquired

At a Glance

Complement factor H deficiency may be inherited from a CFH gene variant or acquired when anti-factor H autoantibodies block the protein. Distinguishing the subtype helps clinicians choose treatment, monitor relapse, and assess implications for family members.

Whether your diagnosis is aHUS (Atypical Hemolytic Uremic Syndrome) or C3G (C3 Glomerulopathy), the underlying problem is often a lack of protection from your own immune system. However, the reason why that protection is missing usually falls into one of two categories: it was either written into your DNA from birth or developed later as an autoimmune reaction [1][2].

Understanding which “flavor” of deficiency you have—inherited susceptibility or acquired autoantibody—is one of the most important steps in your care. While both lead to the same overactive immune response, they require individualized tools to manage and carry different implications for your family [3][4].

The Inherited Path: Genetic Variants

In the inherited form of the disease, you are born with a germline mutation—a permanent change in the instructions your body uses to build the Factor H (FH) protein [5]. Across varying cohorts, CFH variants are identified in approximately 15–20% of people with aHUS, though exact rates differ depending on whether pathogenic variants in any complement gene are included [6].

These genetic risk variants usually disrupt regulation in one of two ways:

  1. Quantitative Deficiency: Your body simply doesn’t produce enough Factor H protein in the blood [7][8].
  2. Qualitative (Functional) Deficiency: Your body makes normal levels of the protein, but a structural defect prevents it from effectively gripping onto the surface of your cells to protect them [9][10].

The “Two-Hit” Concept

Having an inherited mutation does not mean you will be sick your whole life. In fact, many people carry these mutations and never develop symptoms. This is known as incomplete penetrance [5]. Doctors often describe this using a “two-hit” model: your genetics provide the first “hit” (a vulnerability), but it often takes a second “hit”—like a viral infection, pregnancy, or surgery—to actually trigger the active disease [11][12].

The Acquired Path: Autoantibodies

In the acquired form of the disease, your body makes the Factor H protein perfectly, but your immune system mistakenly identifies it as a “threat” [13]. Your immune system then produces autoantibodies—specialized proteins that stick to Factor H and block it from doing its job [14].

This is essentially an “autoimmune” version of the deficiency. It is most common in children and often appears suddenly after an infection [15][16].

The Missing “Cousins”: The CFHR1/CFHR3 Deletion

You may see the terms CFHR1 and CFHR3 in your lab reports. These are “Factor H-Related” proteins [17].

Scientists have discovered a risk association: in some cohorts, up to 90% of children who develop the acquired (anti-Factor H antibody) form of this disease have a homozygous deletion of the genes for these two “cousin” proteins [18][15].

While researchers are still studying why this happens, a leading hypothesis suggests it involves a case of “mistaken identity.” Because the body is missing these proteins, the immune system may never “learn” tolerance to them. When the immune system later encounters an infection with similar-looking proteins, it attacks, creating autoantibodies that cross-react with the main Factor H protein [13]. It is important to note that the deletion is a risk association, neither necessary nor sufficient by itself to cause the disease.

Why the Subtype Matters for You

Identifying your subtype isn’t just about giving the disease a name; it directly helps your medical team design phenotype- and evidence-based treatment pathways [3].

Treatment Strategy

  • For Inherited Cases: Since the problem is a genetic susceptibility, treatment often focuses on using medications like eculizumab or ravulizumab to block the immune system’s downstream attack stage [3].
  • For Acquired Cases: Because the problem is caused by antibodies, doctors in severe cases may use plasma exchange (plasmapheresis) to physically filter the antibodies out, or immunosuppressive drugs to stop your body from making new ones. However, complement inhibition may also be used as a bridge or for ongoing TMA [4][19].

Relapse and Monitoring

The acquired form of the disease can relapse. Doctors track your risk by measuring your antibody titer, though titer alone does not reliably predict relapse; it must be interpreted alongside kidney function, proteinuria, and clinical status [18][14]. In contrast, the inherited form is a persistent underlying risk that may be re-triggered by future illnesses [5].

Family Planning

If you have the inherited form, your family members may also carry the variant. Genetic counseling is recommended to help your family understand their risks [3]. If you have the acquired form, it is less likely to be passed directly to children, though the underlying CFHR1/3 deletion risk factor can be inherited [20].

Regardless of your subtype, the goal of treatment is to safely regulate your complement system and protect your organs from further damage [21][2].

Common questions in this guide

How are inherited and acquired complement factor H deficiency different?
Inherited deficiency results from a CFH gene change present from birth that affects how much Factor H is made or how well it works. Acquired deficiency occurs when the immune system makes autoantibodies that attach to and block Factor H. Both forms can allow excessive complement activity and may be associated with aHUS or C3G.
Does carrying a CFH variant mean I will develop disease?
No. Many people with a CFH variant never develop symptoms because these variants have incomplete penetrance, meaning the genetic risk does not affect every carrier. An infection, pregnancy, or surgery can act as a second trigger in someone who is susceptible.
What does a positive anti-Factor H autoantibody result mean?
It means the immune system has made antibodies that attach to Factor H and may block its protective function. This supports an acquired form of complement dysregulation, but the result should be interpreted with kidney function, protein in the urine, and the overall clinical picture.
Does a CFHR1/CFHR3 deletion cause complement factor H deficiency?
Not by itself. A two-copy deletion of CFHR1 and CFHR3 is associated with acquired anti-Factor H antibodies, especially in children, but it is neither required nor sufficient to cause disease. Doctors interpret this result with antibody testing and clinical findings.
How does the genetic or acquired subtype change treatment?
For an inherited susceptibility, clinicians may use complement-blocking medicines such as eculizumab or ravulizumab. Severe acquired disease may be treated with plasma exchange to remove antibodies and immunosuppressive medicines to reduce new antibody production; complement inhibition may also be used temporarily or for ongoing injury to small blood vessels.
How is relapse monitored in acquired disease?
Doctors may measure the anti-Factor H antibody level, but that number alone does not reliably predict relapse. They also follow kidney function, protein in the urine, and your overall clinical status. In inherited disease, the underlying risk remains and may be triggered again by a future illness.
Can complement factor H deficiency affect my children or siblings?
If the condition is linked to an inherited CFH variant, relatives may carry the same genetic susceptibility, so genetic counseling can help decide whether testing is appropriate. Acquired autoantibodies are less likely to be passed directly to children, although a CFHR1/CFHR3 deletion can be inherited. A genetic counselor or specialist can explain the family-specific risk.

Get notified when new evidence is published on complement factor H deficiency.

We monitor PubMed for new peer-reviewed studies on this topic and email a short summary when something meaningful changes.

References

References (21)
  1. 1

    Clinical and Genetic Characteristics of Atypical Hemolytic Uremic Syndrome in Children: A Chinese Cohort Study.

    Wu D, Chen J, Ling C, et al.

    Nephron 2021; (145(4)):415-427 doi:10.1159/000513009.

    PMID: 33873197
  2. 2

    A Narrative Review of C3 Glomerulopathy: From Pathogenesis to Targeted Therapy.

    Jauhal A, Barr B, Girard L, et al.

    Canadian journal of kidney health and disease 2026; (13()):20543581261442656 doi:10.1177/20543581261442656.

    PMID: 42131278
  3. 3

    Diagnosis and treatment of complement-mediated thrombotic microangiopathies: consensus of the Genetic Diseases Committee of the Chilean Society of Nephrology.

    Musalem P, Bascur N, Sepúlveda RA, et al.

    BMC nephrology 2026; (27(1)):21 doi:10.1186/s12882-025-04739-3.

    PMID: 41495696
  4. 4

    Deficiency of CFHR plasma proteins and autoantibody positive hemolytic uremic syndrome: treatment rationale, outcomes, and monitoring.

    Iorember F, Nayak A

    Pediatric nephrology (Berlin, Germany) 2021; (36(6)):1365-1375 doi:10.1007/s00467-020-04652-x.

    PMID: 32529325
  5. 5

    Functional Characterization of the Disease-Associated N-Terminal Complement Factor H Mutation W198R.

    Cserhalmi M, Uzonyi B, Merle NS, et al.

    Frontiers in immunology 2017; (8()):1800 doi:10.3389/fimmu.2017.01800.

    PMID: 29321782
  6. 6

    Functional characterization of 105 factor H variants associated with aHUS: lessons for variant classification.

    Martín Merinero H, Zhang Y, Arjona E, et al.

    Blood 2021; (138(22)):2185-2201 doi:10.1182/blood.2021012037.

    PMID: 34189567
  7. 7

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

    Merinero HM, García SP, García-Fernández J, et al.

    Kidney international 2018; (93(2)):470-481 doi:10.1016/j.kint.2017.07.015.

    PMID: 28941939
  8. 8

    Genetic analysis and functional characterization of novel mutations in a series of patients with atypical hemolytic uremic syndrome.

    Szarvas N, Szilágyi Á, Csuka D, et al.

    Molecular immunology 2016; (71()):10-22 doi:10.1016/j.molimm.2016.01.003.

    PMID: 26826462
  9. 9

    Disturbed sialic acid recognition on endothelial cells and platelets in complement attack causes atypical hemolytic uremic syndrome.

    Hyvärinen S, Meri S, Jokiranta TS

    Blood 2016; (127(22)):2701-10 doi:10.1182/blood-2015-11-680009.

    PMID: 27006390
  10. 10

    Disease-linked mutations in factor H reveal pivotal role of cofactor activity in self-surface-selective regulation of complement activation.

    Kerr H, Wong E, Makou E, et al.

    The Journal of biological chemistry 2017; (292(32)):13345-13360 doi:10.1074/jbc.M117.795088.

    PMID: 28637873
  11. 11

    Defining the genetics of thrombotic microangiopathies.

    Vieira-Martins P, El Sissy C, Bordereau P, et al.

    Transfusion and apheresis science : official journal of the World Apheresis Association : official journal of the European Society for Haemapheresis 2016; (54(2)):212-9.

    PMID: 27177491
  12. 12

    Successful term pregnancy after renal transplant in end-stage renal disease with complement factor H-related mutation: A case report.

    Balwani MR, Pasari A, Kashiv P, et al.

    World journal of transplantation 2026; (16(1)):113117 doi:10.5500/wjt.v16.i1.113117.

    PMID: 41607808
  13. 13

    Analysis of Linear Antibody Epitopes on Factor H and CFHR1 Using Sera of Patients with Autoimmune Atypical Hemolytic Uremic Syndrome.

    Trojnár E, Józsi M, Uray K, et al.

    Frontiers in immunology 2017; (8()):302 doi:10.3389/fimmu.2017.00302.

    PMID: 28424685
  14. 14

    Anti-complement-factor H-associated glomerulopathies.

    Durey MA, Sinha A, Togarsimalemath SK, Bagga A

    Nature reviews. Nephrology 2016; (12(9)):563-78 doi:10.1038/nrneph.2016.99.

    PMID: 27452363
  15. 15

    Rare Functional Variants in Complement Genes and Anti-FH Autoantibodies-Associated aHUS.

    Valoti E, Alberti M, Iatropoulos P, et al.

    Frontiers in immunology 2019; (10()):853 doi:10.3389/fimmu.2019.00853.

    PMID: 31118930
  16. 16

    Clinical features of children with anti-CFH autoantibody-associated hemolytic uremic syndrome: a report of 8 cases.

    Li Q, Kong X, Tian M, et al.

    Renal failure 2022; (44(1)):1061-1069 doi:10.1080/0886022X.2022.2089167.

    PMID: 35730179
  17. 17

    Elevated surface-bound complement FH alters the function of platelets and monocytes in FHR1/3 null healthy individuals.

    Bhasym A, Bhakuni T, Guchhait P

    Blood cells, molecules & diseases 2019; (79()):102349 doi:10.1016/j.bcmd.2019.102349.

    PMID: 31357175
  18. 18

    Variants in complement genes are uncommon in patients with anti-factor H autoantibody-associated atypical hemolytic uremic syndrome.

    Khandelwal P, Joshi A, Mathur A, et al.

    Pediatric nephrology (Berlin, Germany) 2023; (38(8)):2659-2668 doi:10.1007/s00467-022-05862-1.

    PMID: 36622444
  19. 19

    Factor H autoantibody is associated with atypical hemolytic uremic syndrome in children in the United Kingdom and Ireland.

    Brocklebank V, Johnson S, Sheerin TP, et al.

    Kidney international 2017; (92(5)):1261-1271 doi:10.1016/j.kint.2017.04.028.

    PMID: 28750931
  20. 20

    Clinicopathologic Implications of Complement Genetic Variants in Kidney Transplantation.

    Ren Z, Perkins SJ, Love-Gregory L, et al.

    Frontiers in medicine 2021; (8()):775280 doi:10.3389/fmed.2021.775280.

    PMID: 34912830
  21. 21

    Atypical hemolytic uremic syndrome: Consensus of diagnosis and treatment in Taiwan.

    Tseng MH, Lin SH, Tsai JD, et al.

    Journal of the Formosan Medical Association = Taiwan yi zhi 2023; (122(5)):366-375 doi:10.1016/j.jfma.2022.10.006.

    PMID: 36323601

This page is for informational purposes only and does not constitute medical advice. Your nephrologist, hematologist, immunologist, or genetic counselor should interpret CFH and antibody results and recommend care for your situation.

Guide contents complement factor H deficiency
Research & Literature
02 Symptoms and Emergency Warning Signs 04 The Diagnostic Journey and Essential Lab Tests