In clinical practice, aPL positivity is determined by occurrence of anticardiolipin antibodies (aCL) or of those to the protein co-factor β2-glycoprotein-1 (β2GP1) as measured by enzyme-linked immunosorbent assay (ELISA), or positivity in the functional lupus anticoagulant (LA) test. This evidence concerns the gene FASLG and systemic lupus erythematosus.