Genetic deficiency of C4, C2 or C1q and lupus syndromes. Association with anti-Ro (SS-A) antibodies.

Sera from 15 patients with genetically determined complement component deficiencies were studied for the presence of antibodies to various nuclear antigens. One of three patients with C2 deficiency presented with systemic lupus erythematosus (SLE); all eight patients with C4 deficiency had either SLE or a lupus-like syndrome, and two of four patients with functional C1q deficiency had SLE. Five of nine complement deficiency patients with SLE studied had measurable antinuclear antibody titres, but only two had antibodies against native DNA. Precipitating antibodies against extractable nuclear antigens were found in sera from seven of the 11 complement deficient patients with SLE; one had only antibodies against antigens extracted from calf thymus (ECT), six patients (one with C2 deficiency, four with C4 deficiency and one with C1q deficiency) had anti-Ro (SS-A) antibodies with or without anti-ECT antibodies. The frequency of anti-Ro antibodies in the complement deficient population with SLE (55%) was significantly higher (P less than 0.02) than that of a control population of SLE patients without genetically determined complement deficiencies (27%).