Despite the name of the syndrome (anti-phospholipid), the best-characterized autoantigen in APS is not a phospholipid, but rather a lipid-binding protein that circulates at high levels in the blood (100–200 μg/mL) known as apolipoprotein H (APOH) or beta-2 glycoprotein I (β2GPI). Here, APOH is linked to autoimmune polyendocrinopathy.