Further studies have been carried out in a previously reported family with congenital
antithrombin III (AT III) deficiency due to an abnormal variant of AT III (AT III
Northwick Park). The variant has been identified in five members of the family, three
of whom had a history of venous thrombosis. Inheritance followed an autosomal dominant
pattern. The affected family members have reduced levels of antithrombin heparin cofactor
(41–67%) and progressive antithrombin activity (44–62%) but normal levels of immunoreactive
AT III (91–162%). Two dimensional immunoelectrophoresis (2 DIE) of AT III in the absence
of heparin revealed an abnormal fast-moving peak in addition to the normal peak but
2 DIE in the presence of heparin appeared normal. Further studies confirmed that the
abnormal AT III binds completely to heparin but has no heparin cofactor or progressive
antithrombin activity. These results would be consistent with a mutation affecting
the binding site for thrombin.
Keywords
Antithrombin III - Thrombin - Heparin cofactor