Summary
A family with a high incidence of spontaneous thromboembolism has been investigated
and those members affected were found to have significantly depressed levels of plasma
and serum heparin cofactor activity; i.e., antithrombin III and anti-Xa activity.
Further studies revealed that despite a marked diminution of antithrombin III activity
in these patients measurement of antithrombin III by immunological techniques showed
the levels to be normal. It is concluded that this anomaly represents a defect in
the synthesis of the antithrombin III molecule. The abnormality appeared to be inherited
but the mode of inheritance could not be determined with the available data.