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Abstract Background Antithrombin (AT) is an important anticoagulant in hemostasis. We describe here the characterization of a novel AT mutation associated with clinically relevant thrombosis. A pair of sisters with confirmed type I AT protein deficiency was genetically analyzed on suspicion of an inherited SERPINC1 mutation. A frameshift mutation, c.1247dupC, was identified and the effect of this mutation was examined on the cellular and molecular level. Methods Plasmids for the expression of wild-type (WT) and mutated SERPINC1 coding sequence (CDS) fused to green fluorescent protein (GFP) or hemagglutinin (HA) tag were transfected into HEK293T cells. Subcellular localization and secretion of the respective fusion proteins were analyzed by confocal laser scanning microscopy and Western blot. Results The c.1247dupC mutation results in a frameshift in the CDS of the SERPINC1 gene and a subsequently altered amino acid sequence (p.Ser417LysfsTer48). This alteration affects the C-terminus of the AT antigen and results in impaired secretion as confirmed by GFP- and HA-tagged mutant AT analyzed in HEK293T cells. Conclusion The p.Ser417LysfsTer48 mutation leads to impaired secretion, thus resulting in a quantitative AT deficiency. This is in line with the type I AT deficiency observed in the patients.

Ana Marco-Rico,1,2 Pascual Marco-Vera2,3 1Hemostasis and Thrombosis Department, Hematology Service, University General Hospital Dr. Balmis, Alicante, Spain; 2Biomedical Research Institute (ISABIAL), Alicante, Spain; 3Clinical Medicine Department, Miguel Hernández University, Alicante, SpainCorrespondence: Ana Marco-Rico, Hemostasis and Thrombosis Department, Hematology Service, University General Hospital Dr. Balmis, Pintor Baeza Avenue, 12, Alicante, 03010, Spain, Tel +34 965913863, Fax +34 965913869, Email marco_anaric@gva.esAbstract: Congenital antithrombin (AT) deficiency represents the form of thrombophilia with the highest thrombotic risk. It is characterized by a heterogeneous clinical presentation, depending mostly on the family history of thrombosis and type of genetic mutation. Inherited AT deficiency promotes idiopathic thrombosis at an early age (even in the pediatric population) and at atypical sites. Therefore, a positive family background necessitates ruling out this high-risk thrombophilia at a young age. Studying first-degree relatives, even if they are asymptomatic, is essential to establish thromboprophylaxis and a proper therapeutic approach in case of thrombosis. Patients with congenital AT deficiency require indefinite anticoagulation owing to the high thrombotic recurrence rate. Here, we present four unrelated cases reported in our institution who were diagnosed with hereditary AT deficiency, with a contrasting clinical evolution.Keywords: hereditary antithrombin deficiency, thrombosis, anticoagulation, heparin resistance, SERPINC1 gene mutation

• We identified a novel SERPINC1 gene mutation (c.1A>G p.Met1Val). • The p.Met1Val mutation is associated with significantly lower antithrombin levels and an increased risk of early venous thromboembolism. • Heparin therapy may be ineffective for venous thromboembolism caused by p.Met1Val mutation of SERPINC1 gene. • Novel oral anticoagulants may have favorable anticoagulant effects. [ABSTRACT FROM AUTHOR]

Hereditary antithrombin (AT) deficiency is an autosomal dominant inherited thrombophilia. In three pedigrees of hereditary type I AT deficiency, we identified novel variants c.126delC (p.Lys43Serfs*7), c.165C > G (p.Tyr55*), and c.546delA (p.Lys182Asnfs*102) in the open reading frame encoding AT in each patient. Each of these aberrant variants leads to premature termination of AT protein synthesis. To investigate whether these abnormal variants are involved in the pathogenesis of type I AT deficiency, we analyzed the function of these variants in HEK293 cells. Results of western blot analysis and immunofluorescence microscopy showed that all abnormal variants were expressed intracellularly, but p.Lys43Serfs*7 and p.Tyr55* protein were aggregated in the cells. These three variants were not detected in the spent culture medium, indicating that these novel variants affect protein secretion. In summary, we suggest that these variants in the AT-encoding gene are translated in the cell, but form abnormal proteins that form aggregates and/or inhibit secretion. These results provide insight into novel mechanisms of type I AT deficiency and potential therapies for the condition. [ABSTRACT FROM AUTHOR]

Background Hereditary antithrombin (AT) deficiency is an uncommon autosomal dominant thrombogenic disorder, which can cause venous thromboembolism (VTE). Although conservative treatment options for hereditary AT deficiency-associated VTE such as anticoagulation (warfarin, direct oral anticoagulant, or heparin), intravenous thrombolysis, and recombinant AT are well known, interventional treatment options have not been reported so far. Case summary A 19-year-old man with a family history of thrombogenic diseases, referred to our hospital with left leg pain, was diagnosed with AT deficiency-associated VTE. In the absence of symptomatic relief with intravenous thrombolysis and anticoagulation, he received venous intervention and catheter directed thrombolysis (CDT) for 4 days for left iliac venous thrombosis. Following a second venous intervention, venous thrombus disappeared almost entirely on cross-sectional imaging, and his symptoms improved. He was discharged on apixaban and has been recurrence-free for one and a half years. Discussion This case presents CDT and maintenance therapy with apixaban as possible treatment options for VTE in patients with hereditary AT deficiency, especially following failure of conservative therapy. Individual risks and benefits should be considered when CDT is performed for acute VTE in patients with AT deficiency. [ABSTRACT FROM AUTHOR]

Antithrombin replacement using recombinant human antithrombin (antithrombin gamma) is a well‐tolerated treatment and effective as thromboprophylaxis for a pregnant woman with hereditary antithrombin deficiency. [ABSTRACT FROM AUTHOR]

Goal--The goal of this program is to educate pharmacists about the use of recombinant antithrombin in patients with hereditary antithrombin deficiency. Objectives--At the completion of this program, the reader will be able to: 1. Describe the pharmacology and pharmacokinetics of recombinant antithrombin. 2. Discuss the risks associated with the use of recombinant antithrombin. 3. Discuss the potential benefit of recombinant antithrombin for an individual patient. 4. Apply the information on the use of recombinant antithrombin to a case study. [ABSTRACT FROM AUTHOR]