Lupus erythematosus-like syndrome with selective complete deficiency of C1q.

A 37-year-old Japanese man in previously good health was hospitalized because of swelling of the auricles had discoid erythema of the face. Clinical and laboratory findings satisfied the diagnostic criteria for systemic lupus erythematosus proposed by the American Rheumatism Association. However, serologic studies showed weakly positive antinuclear factor and absence of anti-DNA antibody and lupus erythematosus cells. A striking abnormality was the total absence of serum hemolytic complement activity (CH50). Further studies showed selective complete deficiency of C1q, a subunit of the first component of complement (C1). This is the first reported case of lupus erythematosus-like syndrome with selective complete deficiency of C1q.