Subacute cutaneous lupus erythematosus in multiple members of a family with C2 deficiency.

Deficiency of the second component of complement (C2d) has been associated with systemic lupus erythematosus (LE)-like syndromes as well as recurrent infections. In particular, C2d has been associated with the LE subset of subacute cutaneous LE (SCLE), the presence of anti-Ro antibodies (anti-Ro or SS-A), and the human leukocyte antigen (HLA) types A25, B18, and DR2. A family with C2d in which three members have developed SCLE was observed and studied clinically, serologically, and immunogenetically. Deficiency of the second component of complement was present in all six family members, while anti-Ro was present in only two. There was a strong but incomplete association of C2d and SCLE with HLA-DR2, but the association was not complete with positivity of anti-Ro or antinuclear antibodies. Study of this family reconfirmed the close association of HLA-A25, -B18 and -DR2 with the C2 gene, but indicated a less close association of these loci with serologic markers.