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Objective: Antiphospholipid (aPL) antibodies are present in patients with systemic lupus erythematosus (SLE) and/or antiphospholipid antibody syndrome (APS) and are associated with recurrent thromboses, thrombocytopenia, and pregnancy losses. The presence of aPL antibodies is routinely tested using a standardized ELISA that utilizes cardiolipin as antigen (aCL ELISA). This test, although sensitive, is frequently positive in patients with nonrelated autoimmune disorders and some infectious diseases, making the test less specific. Thus there is a need for more specific tests for aCL with equivalent sensitivity to the standard assay. We evaluated the diagnostic utility of a new aPL antibody test kit with a unique phospholipid mixture designed to be more specific than the standard anticardiolipin ELISA., Methods: aPL antibodies (IgG, IgM) were measured by both a standard ELISA and a new ELISA kit (APhL ELISA Kit, Louisville APL Diagnostics, Inc., Louisville, KY, USA) in the baseline serum from patients enrolled in a 5 year inception cohort, prospective study of early rheumatoid diseases: rheumatoid arthritis (N = 70), SLE (70), scleroderma (45), inflammatory myositis (36), and early undifferentiated connective tissue disease (CTD) (165). Diagnosis was based on standardized criteria and determined at the last study visit. A nested group of patients with Sjogren's syndrome (44) was also defined. Serum from 200 blood donors (BD) served as controls. Patients with known APS (33) and antinuclear cytoplasmic antibody positive renal vasculitis (52) were also studied. Laboratory personnel were blinded to sample diagnostic group., Results: The kit was 90.9% sensitive for detecting APS. Seven patients missed by the kit all had standard aCL values < 40 PL units. Assuming controls do not have APS, the kit was 99.5% specific vs 96.0% for the standard assay. For the patients with CTD, the kit never detected a patient that was not also detected by the standard aCL assay., Conclusion: The APhL ELISA Kit appears to be more specific than the standard aCL ELISA without adding potential false positive results. The new test may be useful for followup study for patients found to be aCL positive by standard assays to increase specificity for aCL screening.

Objective: To investigate the familial basis of antiphospholipid antibodies by studying putative risk factors at the C4 and MHC class II loci., Methods: Autoimmune diseases, anticardiolipin (aCL) and other autoantibodies were studied in 38 first and 2nd degree family members of 3 index cases selected for primary antiphospholipid syndrome (APS) and 33 controls. C4 protein phenotyping and restriction fragment length polymorphism analysis of C4 and MHC class II loci were performed., Results: Nineteen family members (46%) had autoimmune diseases or autoantibodies; aCL were present in 10 family members, 4 of whom had primary APS. Each family had 2 or more subjects with aCL. Among 22 independent haplotypes in family members, there was a high frequency of C4A and C4B deficiency alleles (0.41 vs 0.18 in 66 controls, p = 0.03) and a strong trend toward an increase in MHC DQB1 putative risk factors that share the TRAELDT structural domain. This DQB1 structural domain was present in 4/5 different haplotypes that contained a C4B deficiency genotype; however, neither of 2 different haplotypes with a C4A deletion (one being a common ancestral haplotype) contained this DQB1 putative risk factor. Among the 10 family members who had aCL, 10/20 haplotypes contained a C4 deficiency genotype; moreover, the DQB1 putative risk factor was present in all 16 MHC haplotypes that did not contain a C4A deletion., Conclusion: In these families, expression of an autoimmunity trait as aCL antibody appears to be associated with the coexistence of C4 deficiency alleles with DQB1 alleles that contain the TRAELDT structural domain.