C1QA Gene - Complement C1q A Chain
Key Initiator of the Classical Complement Pathway and Immune Homeostasis
Gene Information Card
| Symbol | C1QA |
|---|---|
| Full Name | Complement C1q A Chain |
| Gene Type | Protein coding |
| Chromosomal Location | 1p36.12 |
| NCBI Gene ID | 712 ncbi.nlm.nih.gov/gene/712 |
| Ensembl ID | ENSG00000173372 |
| UniProt ID | P02745 |
| OMIM ID | 120550 |
| HGNC ID | 1241 |
| Aliases | C1QA_HUMAN, complement component 1, q subcomponent, A chain |
Description
C1QA encodes the A-chain polypeptide of the C1q complex, a 460 kDa heterohexamer composed of 6 A, 6 B, and 6 C chains. C1q is the first component of the classical complement pathway, recognizing immune complexes, apoptotic cells, and pathogens via its globular heads. Binding triggers C1r/C1s activation and downstream complement cascade. C1QA mutations cause hereditary C1q deficiency, strongly linked to systemic lupus erythematosus (SLE) and increased infection risk.
Disease Associations
| Disease category | Pathophysiological mechanism | Genomic evidence |
|---|---|---|
| Systemic Lupus Erythematosus (SLE) | C1q deficiency impairs clearance of apoptotic debris and immune complexes, promoting autoimmunity | OMIM 120550; PMID 10861285 |
| C1q Deficiency (OMIM 613652) | Homozygous loss-of-function mutations in C1QA lead to absent or non-functional C1q protein | ClinVar; PMID 25934856 |
| Hypocomplementemic Urticarial Vasculitis (HUV) | Reduced C1q levels and anti-C1q autoantibodies contribute to vascular inflammation | PMID 24618260 |
| Recurrent Pyogenic Infections | Defective classical pathway opsonization and phagocytosis | OMIM 613652 |
Expression Profile
Tissue Expression
| Tissue | nTPM | level |
|---|---|---|
| Liver | 12.3 | Medium |
| Spleen | 8.7 | Medium |
| Lung | 6.2 | Low |
| Kidney | 4.1 | Low |
| Heart | 3.5 | Low |
Cell Line Expression
| Cell Line | nTPM | Notes |
|---|---|---|
| HepG2 (liver) | 15.2 | Hepatocyte line |
| THP-1 (monocyte) | 9.8 | Macrophage-like |
| A549 (lung) | 5.6 | Epithelial line |
| HEK293 (embryonic kidney) | 2.1 | Low expression |
Data source：Human Protein Atlas（proteinatlas.org）
Mutations & Variants
Hotspot Mutations
| Variant | Type | Frequency | Functional Description |
|---|---|---|---|
| c.205C>T (p.Gln69*) | Nonsense | Rare | Premature stop; loss of C1q function |
| c.622G>A (p.Gly208Arg) | Missense | Rare | Disrupts globular head domain |
| c.1A>G (p.Met1?) | Start loss | Rare | No protein translation |
| c.IVS2+1G>A | Splice donor | Rare | Exon skipping; frameshift |
Mutation functional classification
Loss of Function (LOF)
Homozygous nonsense, frameshift, and splice-site mutations cause complete C1q deficiency, leading to SLE and infections.
Gain of Function (GOF)
No gain-of-function mutations reported for C1QA.
Dominant Negative (DN)
Heterozygous missense mutations may exert dominant-negative effects by disrupting C1q assembly, though clinical penetrance is variable.
View complete mutation data：
Gene Ontology (GO)
Pathways
• Complement cascade (Reactome R-HSA-166658)
• Classical antibody-mediated complement activation (KEGG hsa04610)
• C1q-mediated opsonization and phagocytosis (Reactome R-HSA-173623)
Protein Summary
C1QA encodes the A chain of complement C1q, a 223-amino-acid protein (26 kDa) featuring an N-terminal collagen-like region and a C-terminal globular domain. The collagen region forms triple helices with B and C chains, while the globular heads bind Fc regions of IgG/IgM, C-reactive protein, and apoptotic cell surfaces. C1q is primarily synthesized by macrophages, dendritic cells, and hepatocytes. Defects in C1QA impair immune complex clearance and predispose to SLE.
Related Services
Related Products
| Product name | Cat.No. | Species | Gene ID | |
|---|---|---|---|---|
| C1QA Knockout HEK293 Cell Line | EDJ-KQ50162 | Human | 712 | Details Get a Quote |
| C1QA Knockout HeLa Cell Line | EDJ-KQ52740 | Human | 712 | Details Get a Quote |
| C1QA Knockout A-549 Cell Line | EDJ-KQ61212 | Human | 712 | Details Get a Quote |
| C1QA Knockout HCT 116 Cell Line | EDJ-KQ69704 | Human | 712 | Details Get a Quote |
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