Identification of mothers at risk for congenital heart block and other neonatal lupus syndromes in their children. comparison of enzyme‐linked immunosorbent assay and immunoblot for measurement of anti–ss‐a/ro and anti–ss‐b/la antibodies

Objective. To identify the fine specificity patterns of maternal anti–SS‐A/Ro and anti–SS‐B/La antibodies that are associated with the birth of a child with transient or permanent manifestations of neonatal lupus syndromes, and to suggest a predictor algorithm for use in counseling. Methods. Sera were obtained from 4 groups of mothers: 57 whose children had congenital heart block, 12 whose children had transient dermatologic or hepatic manifestations of neonatal lupus but no detectable cardiac involvement, 152 with systemic lupus erythematosus and related autoimmune diseases, who gave birth to healthy infants, and 30 with autoimmune diseases whose pregnancy resulted in miscarriage, fetal death, or early postpartum death unrelated to neonatal lupus. Antibodies to SS‐A/Ro and SS‐B/La were assessed by enzymelinked immunosorbent assay (ELISA) and by sodium dodecyl sulfate (SDS)‐immunoblot. Results. Anti–SS‐A/Ro antibodies were identified by ELISA in 100%, 91%, 47%, and 43% of the mothers of infants with heart block, with transient neonatal lupus, healthy infants, and fetal death, respectively. High titers of anti–SS‐A/Ro antibodies were present more often in mothers of children with cardiac disease or transient neonatal lupus than in either of the other 2 groups. Maternal antibodies to SS‐B/La were detected by ELISA in 76% of the heart block group, 73% of the cutaneous neonatal lupus group, 15% of the group with healthy children, and 7% of the fetal death group. On SDS‐immunoblot, sera from 91% of the heart block group mothers who had antibodies to SS‐A/Ro but not to SS‐B/La recognized at least 1 SS‐A/Ro antigen, with significantly greater reactivity against the 52‐kd component. In contrast, only 62% of the anti–SS‐A/Ro positive, anti–SS‐B/La negative responders in the healthy group recognized the 52‐kd and/or the 60‐kd component. Although there was no profile of anti–SS‐A/Ro response unique to the mothers of children with heart block or cutaneous manifestations of neonatal lupus, only 1% of the healthy infants were born to mothers with antibodies directed to both the 52‐kd SS‐A/Ro and 48‐kd SS‐B/La antigens and not to the 60‐kd SS‐A/Ro antigen. Conclusion. Women with antibodies to both SS‐A/Ro and SS‐B/La have an increased risk of giving birth to children with neonatal lupus, especially if the anti‐SS‐A/ Ro response identifies the 52‐kd component on SDS‐immunoblot. Women whose sera contain only anti‐SS‐A/Ro antibodies in low titer and only recognize determinants that are altered by conditions of SDS‐immunoblot have a low risk for giving birth to a child with neonatal lupus. Specific antibody profiles do not distinguish among the manifestations of the neonatal lupus syndromes.