SLE like syndrome and functional deficiency of C1q in members of a large family.

Two sisters and a brother from one family are described whose sera were deficient in haemolytic complement function. This defect was restored by addition of purified C1q. In their sera, C1q like material was found, whereas C1r and C1s were normal or increased in concentration, as were the other complement components tested. All three had suffered from glomerulonephritis during childhood. A renal biopsy in the brother recently disclosed a membranous glomerulopathy stage 1; otherwise, he is apparently healthy. In both sisters, a systemic lupus erythematosus like disease became manifest at the age of 20 and 23, respectively, resulting in the death of one of them. In the serum of these three family members, the C1q like material was antigenically deficient compared with normal C1q and had, on sucrose gradient analysis, a molecular weight of approximately 65,000 daltons. It did not bind to C1r and C1s. Binding of the dysfunctional C1q to aggregated human gammaglobulin could be demonstrated. On double immunodiffusion analysis, the abnormal C1q was identical with reduced and alkylated C1q. The possible structure of the abnormal C1q molecule is discussed.