Neonatal Lupus: Bedside to Bench and Back

Abstract

Isolated congenital heart block (CHB) detected in utero is strongly associated with autoantibodies reactive with the intracellular soluble ribonucleoproteins 48 kD SSB/La, 52 kD SSA/Ro, and 60 kD SSA/Ro. An erythematous skin rash with a predilection for the scalp and periorbital area, most often apparent in the first few postnatal months, is also highly associated with these maternal antibodies. The permanent cardiac disease and transient cutaneous disease are the most common manifestations of the neonatal lupus syndromes. Fetal and neonatal disease are presumed to be due to the transplacental passage of these IgG autoantibodies from the mother, who may have systemic lupus erythematosus (SLE), Sjögren's syndrome, or be entirely asymptomatic, into the fetal circulation. The fetal heart appears to be uniquely vulnerable, since complete block has never been described in the mothers despite exposure to identical circulating levels of the autoantibodies. Extensive work from several laboratories has resulted in the molecular characterization of the maternal autoantibody responses and the cloning of genes expressing the cognate antigens whose structural features suggest a role in transcriptional regulation. While the precise pathogenetic mechanism of autoantibody mediated tissue injury is not denned it has been demonstrated in adult rabbit and human fetal hearts that sera containing anti-SSA/Ro antibodies induce atrioventricular block and inhibit L-type calcium currents (I_Ca) in isolated ventricular myocytes. From a clinical perspective the current data suggest that there is not a unique profile of maternal antibody response that predicts the development of neonatal lupus. However, a low risk profile is one in which the titer of anti-SSA/Ro antibodies is low and neither the 60 kD or 52 kD component is recognized on SDS-immunoblot and there are no detectable anti-SSB/La antibodies. Although the fetal disease is called neonatal lupus, this is clearly a misnomer since only about 25% of mothers actually fulfill criteria for the diagnosis of SLE. Furthermore, asymptomatic mothers do not invariably become ill and if an asymptomatic mother does develop SLE it is generally not life-threatening. The recurrence rate of CHB is low, about 15%, but this is nearly three times higher than the risk for CHB in a primigravida with the putative antibodies. CHB carries a significant mortality, 15–30%, and morbidity; two thirds of children require permanent pacing. While prospective clinical trials of fluorinated steroids in women with anti-SSA/Ro and/or anti-SSB/La antibodies is not likely to be initiated given the very low rate of CHB in these mothers, such trials in fetuses with heart block identified in utero are required before definitive recommendations can be made. Numerous anecdotal cases support the use of dexamethasone for treatment of effusions and hydrops and possibly incomplete block. To further efforts both at the bench and bedside, national registries have been established in the U.S. and Canada.

Key Words:

• neonatal lupus
• congenital heart block
• anti-SSA/Ro antibodies
• anti-SSB/La antibodies