Heterogeneity of antiphospholipid antibodies in identical twins

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Background: Autoantibodies to cardiolipin-β 2-glycoprotein I complex have been linked with the antiphospholipid antibody syndrome, characterized by arterial and venous thrombosis and recurrent pregnancy losses. Several studies have suggested a genetic predisposition of the development of these antibodies.
Cases: We report a pair of identical twins who were positive for heterogeneous antiphospholipid antibodies. Both of them were positive for anticardiolipin-β 2-glycoprotein I antibodies and VDRL, however, only twin 1 had prolonged activated partial thromboplastin time and lupus anticoagulant. They shared the HLA haplotype that included the class II antigens DR4, DQ8, which have previously been reported the association with antiphospholipid antibody production. Conclusion: Our report suggests that genetic contributions are not the sole determinant of autoantibody production in antiphospholipid antibody syndrome. The involvement of environ-mental factors may be suggested.