C2 deficient systemic lupus erythematosus: its association with anti-Ro (SSA) antibodies.

C2 deficiency is the most common complement component deficiency. While individuals with C2 deficiency may be completely normal, a lupus erythematosus-like disease process has developed in some. A 28-year-old woman had a chronic photodermatitis, arthralgias, and mesangial lupus nephritis, She has C2 deficiency associated with an HLA-Dw2 transplantation antigen. Her serum has shown antibodies to the macromolecule Ro (the A antigen in Sjögren's syndrome), while failing to demonstrate antinuclear antibodies in routine laboratory determinations.