Neonatal lupus (NL) is a passively transferred autoimmune disease. It occurs in about 1 to 2 percent of babies born to mothers with autoimmune disease, primarily systemic lupus erythematosus (SLE) and Sjögren’s syndrome, and antibodies to SSA/Ro and/or SSB/La [1,2]. However, many cases occur in children of mothers who have the same autoantibodies, but who do not have symptoms of lupus or other autoimmune disease at the time of the baby's birth. About half of these mothers go on to develop autoimmune disease (more commonly Sjögren syndrome than SLE) . The most serious complication of NL is complete heart block (about 10 percent have an associated cardiomyopathy at the initial diagnosis or develop it later).
Neonatal lupus (NL) is presumed to result from transplacental passage of maternal anti-SSA/Ro and/or anti-SSB/La antibodies. Ro and La molecules are thought to form a single particle that is present in all cells. The precise mechanism of injury to specific tissues, such as the skin and heart, is not known. The pathogenesis of disease probably involves more than simple transplacental passage of antibodies, since the disease is rare, even in mothers who have these antibodies, and there can be discordance of disease even in monozygotic twins [4,5]. Anti-Ro/SSA and anti-La/SSB antibodies are associated with a variety of clinical syndromes in adults. (See "The anti-Ro/SSA and anti-La/SSB antigen-antibody systems".)
Autoantibodies — Several studies have established the association between anti-SSA/Ro and anti-SSB/La antibodies and NL by prospectively monitoring offspring of women with anti-Ro/SSA and anti-La/SSB antibodies as follows:
- In a report of 100 women with anti-Ro/SSA antibodies and an autoimmune disease who were prospectively monitored, beginning prior to conception, only two of the mothers had pregnancies that were complicated by congenital complete heart block (detected by fetal echocardiography at 20 and 22 weeks) . The incidence of complete heart block was 2 percent (95% CI 0.5-7 percent) in first-observed pregnancies, 1.8 percent of live births, and 1.7 percent of all pregnancies.
- A similar risk was noted in two other reports. In one series of 124 pregnancies in 112 women with anti-Ro/SSA antibodies, with or without anti-La/SSB antibodies, the risk was 1.6 percent . In another series of women with anti-SSA/Ro, 1 of 99 first-observed pregnancies was complicated by complete heart block .
- In another prospective study of 98 anti-SSA/Ro exposed pregnancies, three offspring had first degree block, three had third degree block, and four had cutaneous neonatal lupus .
These results are consistent with a crude estimate based upon the 0.5 percent prevalence of anti-SSA/Ro antibodies in asymptomatic pregnant women and the rate of congenital heart block (1 in 15,000 to 1 in 22,000 live births) [4,10].