A novel 4 base pair deletion mutation inducing type I antithrombin deficiency

Antithrombin (AT) deficiency is an important hereditary predisposition to venous thrombosis and results from heterogeneous genetic abnormalities. It is generally classified into types I (quantitative) and II (qualitative) on the basis of plasma antigen and activity level of AT. The type I AT deficiency is characterized by a reduced plasma level of the antigen and activity usually to approximately 50% of normal value and the absence of dysfunctional molecules in plasma. The first update of the AT mutation database published in 1993 listed 39 distinct mutations in coding sequences and 9 partial or whole deletions identified in the type I deficiency (1), and a number of new variants have been reported after that (2). We report here a previously undescribed 4-bp deletion mutation in the AT gene inducing the type I deficiency.