Antithrombin (AT) is a major physiological inhibitor of hemostasis. We report 22 novel
antithrombin gene (SERPINC1) mutations associated with
antithrombin deficiency in 17 French and five German families. They were all present at the heterozygous state. Nine missense mutations accounted for type I deficiency, defined by equally low
antithrombin activity and
antigen level. Most of them (7/9) affected highly conserved
serpin residues and were associated with
venous thrombosis occurring at a young age (before age 32). One splice site, one
nonsense mutation, three small deletions and one insertion were also identified as a cause for type I
antithrombin deficiency. Seven other missense mutations were identified in type II or unclassified AT deficiency; g.5270C>T (p.T147I, T115I) and g.5281A>T (p.I151F, I119F) change residues in the
heparin binding region, g.13267C>G (p.P439A, P407A) and g.13271T>C (p.F440S, F408S) affect
amino acids in the pleiotropic region, g.2372G>A (p.G25D, G-8D) changes a
signal peptide amino acid, g.2456G>C (p.C53S, C21S) affects one of the three
disulfide bonds of the
protein, and g.7585A>T (p.M347K, M315K) changes a nonconserved residue on strand 2C.