Five novel and four recurrent point mutations in the antithrombin gene causing venous thrombosis.

We analyzed the antithrombin (AT) gene in 9 unrelated Japanese patients with thrombotic disease. All 7 exons, the splice junctions, and the 5'-flanking region of the AT gene were amplified by polymerase chain reaction and sequenced directly. Nine different point mutations, all in the heterozygous state, were identified. Five novel (M-32T, M89K, L146H, Q159X, and L409P) and 2 previously reported (R132X and R359X) point mutations were identified in patients with type 1 deficiency. Two different missense mutations, R393C and R393H, located in the protease reactive site were detected in patients with type 2 deficiency. No other sequence abnormalities in the AT gene were detected by direct sequencing. None of the mutations was present in 100 alleles from 50 unrelated Japanese control subjects Although type 1 deficiency was diagnosed in patient 7 on the basis of approximately 50% AT antigen and activity levels, the data indicated that the novel L409P mutation is a type 2 pleiotropic effects (PE) deficiency because its location in the C-terminal portion of the reactive site is similar to the locations of reported PE type mutations, and it is highly conserved among other serpins.