Inherited antithrombin III deficiency is associated with an increased risk of thromboembolism. Using recombinant-DNA techniques, we isolated a molecular probe for the antithrombin III structural gene and identified a common DNA polymorphism within the gene. We found that there is genetic heterogeneity in this disorder. In one family, the antithrombin III gene was deleted in affected members, whereas in another no deletion occurred. Use of the DNA polymorphism should allow identification and further characterization of abnormal antithrombin III genes.
