CFB

Chr 6

complement factor B

Also known as: AHUS4, ARMD14, BF, BFD, CFAB, CFBD, FB, FBI12

This gene encodes complement factor B, a component of the alternative pathway of complement activation. Factor B circulates in the blood as a single chain polypeptide. Upon activation of the alternative pathway, it is cleaved by complement factor D yielding the noncatalytic chain Ba and the catalytic subunit Bb. The active subunit Bb is a serine protease which associates with C3b to form the alternative pathway C3 convertase. Bb is involved in the proliferation of preactivated B lymphocytes, while Ba inhibits their proliferation. This gene localizes to the major histocompatibility complex (MHC) class III region on chromosome 6. This cluster includes several genes involved in regulation of the immune reaction. Polymorphisms in this gene are associated with a reduced risk of age-related macular degeneration. The polyadenylation site of this gene is 421 bp from the 5' end of the gene for complement component 2. [provided by RefSeq, Jul 2008]

GeneReviewsResearchGenerating clinical summary…

Primary Disease Associations & Inheritance

UniProtMacular degeneration, age-related, 14
UniProtHemolytic uremic syndrome, atypical, 4
UniProtComplement factor B deficiency

Clinical highlights

Gene-disease validity (ClinGen)
atypical hemolytic-uremic syndrome with B factor anomaly · ADModerateconsider for supplementary testing2 gene-disease associations curated in total
Interpreting a novel variant
This gene is strongly intolerant of loss-of-function variation in the population, so LoF variants warrant close attention. No curated mechanism annotation is available — see the mechanism card for the computational prediction and its caveats.Based on population constraint only.
7
Active trials
263
Pubs (1 yr)
P/LP submissions
P/LP missense
0.52
LOEUF
Multiple*
Mechanism· predicted
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GeneReview available — CFB
Authoritative clinical overview · Recommended first read
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Some data sources returned errors (1)

omim: Error: OMIM fetch failed: 429

Population Genetics & Constraint

gnomAD v4 — loss-of-function & missense intolerance

Moderate LoF intolerance
LoF Constraint?
0.52LOEUF
pLI 0.000
Z-score 3.99
OE 0.33 (0.220.52)
Moderately constrained

More LoF-intolerant than ~75% of genes

Missense Constraint?
1.48Z-score
OE missense 0.79 (0.720.87)
326 obs / 410.4 exp
Tolerant

Mild missense constraint

Observed / Expected Ratios?
LoF OE?0.33 (0.220.52)
00.351.4
Missense OE?0.79 (0.720.87)
00.61.4
Synonymous OE?0.93
01.21.6
LoF obs/exp: 14 / 41.9Missense obs/exp: 326 / 410.4Syn Z: 0.73

ClinVar Variant Classifications

0 submitted variants in ClinVar

Protein Context — Lollipop Plot

CFB · protein map & ClinVar variants

Showing all ClinVar variants across the protein. Search a specific variant to highlight its position.

Clinical Trials

Active and recruiting trials from ClinicalTrials.gov

BAG3 Mutation Associated Dilated Cardiomyopathy

ALXN2350 in Adult Participants With BAG3-Associated Dilated Cardiomyopathy

RECRUITING
NCT07218887Phase PHASE1, PHASE2Alexion Pharmaceuticals, Inc.Started 2025-10-24
ALXN2350
Complement 3 Glomerulopathy

A Study of Complement 3 Glomerulopathy (C3G) Patients Treated With Iptacopan Through an Early Access Program in Spain

NOT YET RECRUITING
NCT07598448Novartis PharmaceuticalsStarted 2026-09-10
Migraine DisordersPainAutoimmune Diseases

The Role of Cytokines and Regulatory T Lymphocytes in Migraine Pathophysiology.

RECRUITING
NCT06426316Phase NAUniversity Hospital, Clermont-FerrandStarted 2025-06-02
Blood test
Obesity

Adipose Tissue Gene Expression and Metabolomics Links to the Gut Microbiome-brain Axis

RECRUITING
NCT06869941Institut d'Investigació Biomèdica de Girona Dr. Josep TruetaStarted 2025-08-05
Obesity

Involvement of the Gut Microbiota-brain Cross-talk in the Loss of Eating Control

RECRUITING
NCT05646901Institut d'Investigació Biomèdica de Girona Dr. Josep TruetaStarted 2022-12-12
Melanoma

A Trial to See if the Combination of Fianlimab With Cemiplimab Works Better Than Pembrolizumab for Preventing or Delaying Melanoma From Coming Back After it Has Been Removed With Surgery

ACTIVE NOT RECRUITING
NCT05608291Phase PHASE3Regeneron PharmaceuticalsStarted 2023-01-16
FianlimabCemiplimabPembrolizumab
Mild Cognitive ImpairmentAlzheimer's DiseaseAlzheimer's Disease, Early Onset

Development of a Database to Investigate Digital and Blood-Based Biomarkers and Their Relationship to Tau and Amyloid PET Imaging in Older Participants Who Are Cognitively Normal (CN), Have Mild Cognitive Impairment (MCI), or Have Mild-to-Moderate AD Dementia

RECRUITING
NCT06584357GAP Innovations, PBCStarted 2024-09-26
Biomarker Data CollectionMK6240