Complement genes on chromosome 6

Early complement component depletion and mixed cryoglobulinemia in a "healthy" family

A family containing two apparently healthy brothers with profound early complement component depletion (C1, C4, C2) and mixed IgG-IgM polyclonal cryoglobulins was studied. The cryoglobulins possessed rheumatoid factor activity and depleted early complement components in normal human serum. Circulating immune complexes could not be detected by utilizing standard methods. The phenomenon was not HLA-linked. This study demonstrates the familial occurrence of a chronic hypocomplementemic state associated with cryoglobulinemia in clinically normal subjects.

Familial deficiency of two subunits of the first component of complement. C1r and C1s associated with a lupus erythematosus-like disease

Complete absence of C1r and almost complete absence of C1s were found in 4 of 8 living siblings. Two of the 4 suffer from a syndrome that combines discoid lupus erythematosus and nondeforming rheumatoid-like arthritis; one of the siblings has mild nephritis. The other 2 C1 deficient family members are clinically well. Evidence from this and other families suggests that deficiency of C1 components or C4 is associated with higher risk of developing a lupus-like disease than is deficiency of C2.