F2 and deep vein thrombosis: Newly defined sub-classes of aPLs, including antibodies to β2GPI Domain 1 (β2GPI D1) and β2GPI Domain 4/5 (β2GPI D4/5) and anti-phosphatidylserine/prothrombin (aPS/PT), have been associated with thrombosis; although there is not yet sufficient evidence to include these antibodies into APS diagnostic criteria (Atsumi et al., 2000; Bertolaccini et al., 2005, 2011; Forastiero et al., 2005; Bizzaro et al., 2007; Sanmarco et al., 2007).