Antibodies to amino acid 200-239 (p200) of Ro52 as serological markers for the risk of developing congenital heart block

Abstract

Maternal autoantibodies to the p200-epitope of Ro52 have been suggested to correlate with development of congenital heart block. The aim of the present study was to evaluate the clinical relevance and predictive value of p200-antibodies in high-risk pregnancies. Sera from 515 Finnish, Swedish and American women were included in the study. Sera originated from 202 mothers with an infant affected by second- or third-degree atrioventricular block (AVB), 177 mothers with rheumatic disease having infants with normal heart rate and female blood donors (n = 136). A novel serological assay for Ro52 p200-antibodies with intra- and inter-assay variability of 3% and 3.8% respectively was developed. Mothers of children affected by AVB II-III had significantly higher p200-antibody levels than mothers with rheumatic disease having children with normal heart rate (P < 0.001). In the Swedish cohort, a distinction between foetuses with normal conduction, AVB I, AVB II and III was possible. A significant difference in anti-p200 levels between AVB I and AVB II-III groups compared with foetuses with normal conduction (P < 0.05 and P < 0.01) was observed. Using p200-antibodies as a second step analysis in Ro52-positive pregnancies increased the positive predictive value for foetal cardiac involvement (AVB I, II or III) from 0.39 (0.27-0.51) to 0.53 (0.37-0.68). In conclusion, Ro52 p200-antibodies may occur in women with unaffected children, but levels are significantly higher in mothers of children with congenital heart block and are suggested as a relevant marker in evaluating the risk for foetal AV block.

Figures

Fig. 1

p200 levels in mothers of foetuses with or without AVB II-III. Antibodies to the p200 peptide in maternal sera were measured by ELISA. Sera from all mothers included in the study (n = 515) were tested and p200 antibody levels compared between mothers of foetuses with AVB II-III and mothers with rheumatic disease and foetuses with normal heart rate (NHR), P < 0·0001. The study population includes mothers from Finland, Sweden and the USA. Female blood donors were from Finland (n = 31) and Sweden (n = 105).

Fig. 2

Levels of p200 antibodies in Ro52-positive Finnish, Swedish and American mothers of foetuses with or without AVB II-III. The cohorts were separated to allow comparisons between the three nationalities. Only Ro52-positive women are included. Separating the populations, the p200 levels are significantly different between mothers of foetuses with AVB II-III and mothers of foetuses with normal heart rate (NHR) in the Swedish and American populations, but not in the Finnish population.

Fig. 3

Maternal diagnosis and p200 levels in Finnish, Swedish and American patients. (a) The nationally grouped Ro52-positive mothers were stratified also by their diagnosis of SS, SLE or other rheumatic disease (including RA, MCTD, UCTD, scleroderma or asymptomatic women with Ro52 antibodies). (b) Analysing the Ro52-positive mothers, disregarding the infant diagnosis, the Finnish mothers with SS have significantly higher levels of p200 levels than mothers with SLE (P < 0·05).

Fig. 4

p200 antibody levels are equally high in AVB I and AVB II-III. In the Swedish cohort all pregnancies were systematically followed by foetal Doppler echocardiography, allowing further distinction of foetal diagnosis into AVB II-III, AVB I and normal conduction (NC). p200 antibody levels in mothers with AVB II-III as well as AVB I foetuses were significantly higher than p200 antibody levels in mothers of foetuses with NC. There was not a significant difference in p200 antibody levels between mothers of foetuses with AVB I and AVB II-III.

Fig. 5

Discrimination performance of the p200 antibody ELISA. ROC analysis of the Swedish cohort including healthy controls optimizes the cut-off at the p200 index = 30, which results in a sensitivity of 90·5% and a specificity 96% and a positive likelihood ratio (+LR) of 23 of cardiac involvement (AVB I, II or III).