In this work we analyzed: (i) in vitro whether anti-β2-GPI antibodies from APS patients may induce both a HMGB1 cellular relocation by activation of its putative receptor RAGE in platelets and monocytes and, (ii) ex vivo, serum levels of HMGB1/soluble RAGE (sRAGE) in APS patients and their possible correlation with clinical manifestations. The gene discussed is AGER; the disease is autoimmune polyendocrinopathy.