C1QB Gene

The C1QB gene (C1QB stands for Complement C1q B Chain) is a protein-coding gene located at chromosome 1p36.12.

The C1QB gene encodes the B-chain polypeptide of the serum complement subcomponent C1q, which associates with C1r and C1s to form the first component of the serum complement system. C1q consists of 18 polypeptide chains, including 6 A chains, 6 B chains, and 6 C chains. Each chain contains an N-terminal collagen-like region and a C-terminal C1q globular domain. C1q deficiency is associated with lupus erythematosus and glomerulonephritis.

Diseases associated with C1QB include "familial C1q deficiency."

The C1q complex associates with the proenzymes C1r and C1s to form C1 , the first component of the serum complement system. The collagen-like domains of C1q interact with the Ca(2+)-dependent C1r(2)C1s(2) proenzyme complex. Efficient activation of the C1 component as the first step in the complement cascade, occurs through interaction of the globular heads of C1q with the Fc regions of IgG or IgM antibodies in immune complexes.

1. Bruiners N et al. (2020) A regulatory variant in the C1Q gene cluster is associated with tuberculosis susceptibility and C1qA plasma levels in a South African population. Immunogenetics 72:305-314.
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5. Lopez-Lera A et al. (2014) M. Rothmund-Thomson syndrome and glomerulonephritis in a homozygous C1q-deficient patient due to a gly164ser C1qC mutation. (Letter) J Invest Derm 134: 1152-1154.