Lupus erythematosus associated with genetically determined deficiency of the second component of the complement.

BACKGROUND The gene deletion responsible for the type I human complement C2 deficiency was reported in 1992. The purpose of our study is to evaluate clinical and immunological characteristics of 11 patients with lupus erythematosus and type I C2 deficiency. OBSERVATIONS We observed 5 patients with a homozygous C2 deficiency and 6 with a heterozygous C2 deficiency. Eight patients had systemic lupus erythematosus, 2 had subacute cutaneous lupus erythematosus, and 1 had chronic lupus erythematosus. Photosensitivity was present in 73% of the patients, and 64% tested positive for anti-Ro (SSA) antibodies. Renal involvement that required immunosuppressive therapy was present in 54% of the patients. Ninety percent of the patients tested positive for antinuclear antibodies, and 54% tested positive for anti-double-stranded DNA antibodies. Phenotyping of the fourth component of the complement was performed in 82% of the patients and showed a C4A4B2 phenotype, which is suggestive for the type I C2 deficiency. CONCLUSIONS Most patients with lupus erythematosus associated with C2 type I deficiency are photosensitive, and this is probably related to the presence of anti-Ro (SSA) autoantibodies. The prognosis for those patients is not better than that for patients with lupus erythematosus in general.