Quantitative and qualitative congenital deficiency of antithrombin III: a new molecular variant called ATIII-Barcelona 2.

A Spanish family with a quantitative-qualitative antithrombin III (ATIII) deficiency and thrombotic tendency is reported. The qualitative defect was suggested by the crossed immunoelectrophoresis (CIE) in the presence of heparin in plasma of all those affected. However, the crossed immunoelectrofocusing (CIEF) showed the same ATIII pattern in controls and affected members. Two populations of ATIII were detected by affinity chromatography on heparin-sepharose from affected members' plasma. The ATIII unbound to sepharose beads was devoid of heparin cofactor activity and showed a lack of anodal migration in CIE in the presence of heparin. The ATIII eluted corresponded to normal ATIII. Our data supports the view that an abnormal ATIII molecule is present in all affected family members in the heterozygous state. This is the first reported ATIII variant in which a molecular abnormality produces a lack of affinity for heparin but no changes in its isoelectric point. This familial ATIII deficiency was named ATIII- Barcelona 2.