Biological Characteristics Op Antithrombin III In An Antithrombin III Deficient Family

In the familial AT III deficiency of a Japanese family, the propositus (a-39-yr old female) and her mother had episodes of recurrent thrombosis and their AT III levels as measured immunologically and biologically were below the normal value. In the plasma of her brother, the AT III concentration as measured immunologically was half of the normal value, but his biological antithrombin activity was within the normal range. The progressive antithrombin activity and antifactor Xa activity of plasma samples in this familial AT III deficiency were within the normal range. Measurements of the rate of thrombin neutralization activity revealed that the brother’s plasma was in the normal range, but the plasma of the propositus and of her mother showed rates of thrombin neutralization activity which were somewhat below the normal value. The rate of thrombin neutralization activity per mg protein of AT III was highest in the plasma of the brother, and became slower in the mother, propositus, and pooled normal plasma in that order. In the plasma of this familial AT III deficiency, the rate of Xa neutralization activity was much slower than the normal value. It is postulated that since the antithrombin of the brother of the propositus was found to react as normal in the neutralization of thrombin, he does not have episodes of thrombosis. Such characteristic hyperfunction of antithrombin in the plasma of the brother may be due to some molecular abnormality of AT III within this hereditary deficient family.