Antithrombin deficiency in three Japanese families: one novel and two reported point mutations in the antithrombin gene.

INTRODUCTION: Inherited antithrombin (AT) deficiency is associated with a predisposition to familial venous thromboembolic disease. We analyzed the AT gene in three unrelated patients with an AT deficiency who developed thrombosis. MATERIALS AND METHODS: We analyzed the SERPINC1 gene in three patients. Additionally, we expressed the three mutants in the COS-1 cells and compared their secretion rates and levels of AT activity with those of the wild-type (WT). RESULTS: We identified three distinct heterozygous mutations of c.2534C>T: p.56Arginine → Cysteine (R56C), c.13398C>A: p.459Alanine → Aspartic acid (A459D) and c.2703C>G: p.112 Proline → Arginine (P112R). In the in vitro expression experiments, the AT antigen levels in the conditioned media (CM) of the R56C mutant were nearly equal to those of WT. In contrast, the AT antigen levels in the CM of the A459D and P112R mutants were significantly decreased. The AT activity of R56C was decreased in association with a shorter incubation time in a FXa inhibition assay and a thrombin inhibition-based activity test. However, the AT activity of R56C was comparable to that of WT when the incubation time was increased. CONCLUSIONS: We concluded that the R56C mutant is responsible for type II HBS deficiency. We considered that the A459D and P112R mutants can be classified as belonging to the type I AT deficiency.

Two case reports of inherited antithrombin deficiency: a novel frameshift mutation and a large deletion including all seven exons detected using two methods.

An inherited antithrombin deficiency is an autosomal dominant thrombotic disorder. We identified two pedigrees of inherited type I antithrombin deficiency and two responsible mutations in each. A novel 21-22delAA appeared to have caused a frameshift with a premature termination at amino acid +63 in one patient and a large deletion including all seven exons was identified by multiplex ligation-dependent probe amplification in the other. Some asymptomatic relatives of the second patient had the same mutation. The present findings support the value of using more than one method of gene analysis and of studying the families of probands with inherited thrombotic disorders.