By Gary M. White, MD
Loss-of-function mutations in C1q are sufficient to cause SLE-like manifestations in 90% of cases.
Potential skin manifestations of C1q deficiency include butterfly-like erythema on the face, discoid lupus–type lesions, and symptoms of Raynaud's phenomenon similar to those detected in SLE.
Neurologic symptoms, glomerulonephritis and recurrent and severe infections are common.
CH50 activity and C1q plasma levels are almost zero, but C2, C4, and C1 inactivator levels are usually normal or high. Tests for antinuclear, rheumatoid factor, and anti-Sm antibodies are positive.
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