Summary. Background: Diagnosis of the antiphospholipid syndrome (APS) is difficult as a result of limited specificity of existing assays for detecting clinically relevant antiphospholipid antibodies. Anti-beta2-glycoprotein I (beta2GPI) antibodies play a central role in the disease process of APS. Objectives: We have investigated the relation between antiphospholipid antibodies with specificity for domain I of beta2GPI and thrombosis/pregnancy morbidity in an international multicenter study. Patients/methods: Four hundred and seventy-seven patients derived from nine different centres met the inclusion criterion of having anti-beta2GPI antibodies in their plasma/ serum. Clinical data and results of tests for lupus anticoagulant, anti-cardiolipin antibodies and anti-beta2GPI antibodies were established at the different centres of inclusion. After being retested for the presence of IgG and/or IgM anti-beta2GPI antibodies, the samples were tested for the presence of IgG-directed against domain I of beta2GPI and results were correlated with the thrombotic and obstetric history. Results: Re-testing for the presence of anti-beta2GPI antibodies resulted in inclusion of 442/477 patients. IgG class anti-domain I antibodies were present in plasma of 243/442 patients (55%).201/243 (83%) had a history of thrombosis. This resulted in an odds ratio of 3.5 (2.3-5.4, 95% confidence interval) for thrombosis. Anti-domain I IgG antibodies were also significantly correlated with obstetric complications [odds ratio: 2.4 (1.4-4.3, 95% confidence interval)]. Conclusion: In this multicenter study, the detection of IgG antibodies that are directed against domain I of beta2GPI proved to be more strongly associated with thrombosis and obstetric complications than those detected using the standard anti-beta2GPI antibody assay.

Well-defined US changes in the major salivary glands summarized in our novel scoring system were typical of SS patients. Advanced structural changes found on US imaging almost invariably represent SS salivary gland involvement.

This is the first report in which the cut-off values for aCL and anti-beta(2)GPI in children are expressed in concentrations of monoclonal antibodies. Low titres of aCL, which were identified frequently in apparently healthy children, were hypothesized to be the result of previous infections. The high mean value of IgG anti-beta(2)GPI observed in preschool children was an unexpected result of the study and might indicate a default response to nutritional exposure to beta(2)GPI in this age group.

This is the largest cohort to date focusing on the prevalence of anti-Ku antibodies in patients with SSc. The case-control approach was able to demonstrate a clinically distinct subset of anti-Ku positive patients with SSc with only relative clinical differences in skeletal features. However, the notable exceptions were signs of myositis. This shows the importance of anti-Ku antibody detection for the prediction of this specific clinical subset.

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