The prevalence of antibodies to anionic phospholipids in patients with the primary antiphospholipid syndrome, systemic lupus erythematosus and their relatives and spouses.

OBJECTIVES Antiphospholipid antibodies (aPL) have been associated with syndromes involving thrombosis, fetal loss and thrombocytopenia. Genetic and environmental conditions are among the factors attributed to the cause of autoimmune diseases such as the antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE). The aim of this study was to determine whether these factors determine the prevalence of aPL. METHODS Three groups of patients were tested for the presence of IgG, IgM and IgA anticardiolipin (aCL), antiphosphatidylinositol (aPI), antiphosphatidylglycerol (aPG) and antiphosphatidylserine (aPS) antibodies: (i) patients with primary APS (PAPS); (ii) patients with SLE and secondary APS; and (iii) patients with SLE without APS. First-degree relatives and spouses of patients with SLE/APS were also tested for circulating aPL. RESULTS IgG aPL were particularly prevalent in patients with PAPS. IgG aPI and aCL were more prevalent in patients with PAPS than the IgM equivalents (P < 0.0001). Notably, none of the patients with PAPS had IgA aPL. A significantly higher number of relatives of patients with SLE/APS possessed IgG aPL than the normal controls. Except for aPG (P < 0.03), the prevalence of these antibodies in the relatives was not significantly different from patients with SLE/APS. The relatives also had significantly higher prevalence of IgG aPI, aPS and aCL antibodies than IgM aPL antibodies. In contrast, the prevalence of IgG aPL in the spouses was no different than in the healthy controls. CONCLUSIONS Genetic factors, shared by patients and their relatives, seem to have some effect on the prevalence of aPL in the subjects studied, while environmental factors shared by spouses appear to have no influence.