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

Background: The gene deletion responsible for the type 1 human complement C 2 deficiency was reported in 1992. The purpose of our study is to evaluate clinical and immunological characteristics of 11 patients with lupus erythe matosus 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 erythe matosus, 2 had subacute cutaneous lupus erythematosus, and 1 had chronic lu pus erythematosus. Photosensitivity was present in 73% of the patients, and 64% tested positive for anti-Ro (SSA) antibodies. Renal involvement that r equired immunosuppressive therapy was present in 54% of the patients. Ninet y percent of the patients tested positive for antinuclear antibodies, and 5 4% 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 defic iency. Conclusions: Most patients with lupus erythematosus associated with C2 type I deficiency are photosensitive, and this is probably related to the prese nce of anti-Ro (SSA) autoantibodies. The prognosis for those patients is no t better than that for patients with lupus erythematosus in general.