Summary
Inherited antithrombin deficiency is associated with an increased risk of thrombosis,
primarily venous rather than arterial. Most affected individuals have inherited only
a single copy of an abnormal antithrombin (AT) gene. Homozygously affected individuals,
although rare, have a severe thrombotic history of early onset and often affecting
the arteries. We report two new cases of type II HBS (heparin binding site) deficiency
in which the propositi are homozygous for the previously reported mutation 99 Leu
to Phe, and who have a severe thrombotic history. These cases are considered alongside
existing homozygote and compound heterozygote cases.