[Familial lupus erythematosus with partial C4 deficiency].

A report is presented of a family with selective partial C4-deficiency in 3 members, two of whom suffer from systemic lupus erythematosus (SLE). C4-allotyping showed the presence of one "silent gene" for the C4B-locus (C4BQO) in these three cases. Presumably it is not the reduced C4-content per se that plays the essential role in the pathogenesis of familial SLE, but the combination of the C4BQO-allele with the HLA-DR2, which was also present in all three affected persons. However, it is of practical relevance that strikingly low C4-levels in comparison with the C3-levels in patients with early onset of SLE should initiate an investigation of the whole family. Furthermore, the C4-level in this form of familial SLE is not a suitable parameter for ganging disease activity on follow-up control investigations.