One of the rare but important underlying causes is antiphospholipid syndrome (APS), an autoimmune prothrombotic condition associated with persistent antiphospholipid antibodies: lupus anticoagulant (LA), anticardiolipin (aCL), or anti-β2 glycoprotein I (anti-β2GPI). The gene discussed is APOH; the disease is antiphospholipid syndrome.