Genetics of Complement System
The complement system is a cascade of plasma proteins that marks pathogens for destruction, directly lyses bacteria, and amplifies inflammation. Genetic variants in complement regulators have been implicated in COVID-19 severity and Long COVID vascular complications.
This page is for educational and informational purposes only. Not a diagnostic tool. Always consult a qualified healthcare provider.
What is Complement System?
The complement system consists of over 50 proteins that work together to mark pathogens (opsonisation), recruit inflammatory cells, and directly destroy pathogens through the membrane attack complex (MAC). It is activated through three pathways: classical (antibody-triggered), lectin (pattern recognition), and alternative (spontaneous). Dysregulated complement activation drives inflammation and tissue damage — as evidenced in thrombotic microangiopathy, age-related macular degeneration (driven by CFH variants), and COVID-19 coagulopathy. SARS-CoV-2 triggers extensive complement activation, and genetic variants in complement regulators may modify complement-driven pathology in COVID-19 and Long COVID.
Biological pathways commonly discussed in relation to Complement System
Research into Complement System and Innate Immune Effector Cascades has highlighted several biological pathways that may be relevant. Genetic variants within these pathways may influence individual susceptibility, symptom severity, or the trajectory of the condition.
Complement Activation
The three complement activation pathways (classical, lectin, alternative) converge on C3 convertase, cleaving C3 to C3a (anaphylatoxin) and C3b (opsonin). Variants in C3, C4, and pathway-specific components affect activation efficiency.
Complement Regulation
CFH (complement factor H) and CFI inhibit spontaneous alternative pathway activation. CFH variants — particularly the Y402H (rs1061170) variant — are the strongest genetic risk factor for age-related macular degeneration and affect complement regulation in multiple tissues.
Membrane Attack Complex
The terminal complement pathway forms the membrane attack complex (C5b-9) that lyses target cells and pathogens. Variants in C5, C6, C7, C8, and C9 affect MAC assembly.
Complement Opsonisation
C3b and iC3b coat pathogens for phagocytosis by neutrophils and macrophages via CR1 (CD35). CR1 variants affect phagocytic uptake of complement-opsonised targets.
Key genes studied in relation to Complement System
The following genes have been studied in relation to Complement System and Innate Immune Effector Cascades. These genes span the biological pathways most commonly discussed in this area of research.
11 genes total studied in relation to Complement System across the ChronicDNA dataset.
Genetic variants commonly discussed
The following genetic variants (SNPs) are found in genes that have been studied in relation to Complement System. Each variant represents a position in the genome where individuals may carry different alleles.
18 variants total across genes studied in relation to Complement System.
How personal DNA data may provide educational insights
Consumer DNA files from 23andMe, AncestryDNA, and MyHeritage contain raw SNP data. When you upload your file to ChronicDNA, the analysis engine checks your genotype against a curated panel of 80+ genes selected for their relevance to Long COVID, ME/CFS, and connected biological pathways - some of which may relate to areas such as Complement System.
This is not a diagnostic service. Genetic variants do not determine whether you have Complement System, nor do they predict your clinical outcomes. The report is educational - it explains which variants you carry, what the research says about them, and how they fit into the biological pathways most relevant to chronic illness. All results should be discussed with a qualified healthcare provider.
Related conditions and pathways
Complement System shares biological pathways and genetic associations with the following related conditions and areas of research.
Frequently asked questions
What is the complement system?
The complement system is a network of plasma proteins that amplifies innate immune responses by opsonising pathogens, recruiting inflammatory cells, and directly lysing bacteria. It operates through three activation pathways converging on C3 cleavage.
How does complement relate to Long COVID?
SARS-CoV-2 triggers extensive complement activation contributing to endothelial injury, coagulopathy, and inflammation. Genetic variants in complement regulators (CFH, CFI) may modify the degree of complement-driven tissue damage in COVID-19 and potentially Long COVID vascular complications.
What is CFH and why is it important?
CFH (complement factor H) is a critical regulator of the alternative complement pathway, preventing spontaneous C3 activation on healthy host cells. The Y402H variant (rs1061170) in CFH impairs binding to certain glycosaminoglycans, increasing complement activation on affected tissues — most famously causing age-related macular degeneration.
Which complement genes are most studied?
Key genes include CFH, CFI, C3, C4A, C4B, C5, C1Q genes, and CR1. These cover regulation, activation, and effector functions across all three complement pathways.
Explore DNA insights
If you already have DNA data from 23andMe, AncestryDNA, or MyHeritage, upload your raw file to ChronicDNA and receive a personalised educational report covering genes studied in relation to Complement System and connected biological pathways.
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11 genes · 18 variants analysed in relation to Complement System