Antithrombin Dublin (p.Val30Glu): a relatively common variant with moderate thrombosis risk of causing transient antithrombin deficiency

Comparison of antithrombin activity assays in detection of patients with heparin binding site antithrombin deficiency: systematic review and meta-analysis

Antithrombin (AT) deficiency increases the risk for venous thromboembolism, therefore, a highly sensitive assay to identify this condition is crucial. The aim of this paper was to perform a meta-analysis comparing AT activities measured by different AT activity assays in patients with heparin binding site AT deficiency. In addition, the diagnostic sensitivity of selected assays was compared depending on the available data. An extensive literature search was performed considering results with publication date up to July 10, 2021. Seven relevant English-language observational studies, comparing AT activity measured by different AT activity assays in Caucasian Europeans with either the AT Budapest III or AT Padua I mutation were included in meta-analyses. There was no significant difference in AT activity between Labexpert and Innovance in patients with AT Budapest III (P = 0.567) and AT Padua I (P = 0.265), while AT activity determined by HemosIL was significantly higher compared to Innovance for both mutations (AT Budapest III: P < 0.001; AT Padua I: P < 0.001). These results are in line with the results of comparison of diagnostic sensitivity. In patients with AT Budapest III, the AT activity was also higher when measured with Berichrom compared to Innovance (P = 0.002), however, the results of comparison of diagnostic sensitivity across studies were variable. No significant difference (P = 0.117) in AT activity as well as diagnostic sensitivity was observed between Sta-Stachrom and Innovance. The results of our study suggest that Innovance, Labexpert and Sta-Stachrom are the most sensitive activity assays for detection of AT Budapest III and AT Padua I, whereas HemosIL showed considerably lower sensitivity for these two variants. As revealed in our study, the diagnostic sensitivity of AT activity assays to type II heparin binding site AT deficiency is different, and in some assays mutation dependent.

Antithrombin III deficiency in a patient with recurrent venous thromboembolism: A case report

BACKGROUND

Antithrombin III (AT3) deficiency, an autosomal dominant disease, increases the likelihood of an individual developing venous thromboembolism (VTE). Long-term anticoagulation treatment is required for those suffering from AT3 deficiency.

CASE SUMMARY

A man aged 23, who had a history of deep venous thrombosis (DVT), experienced recurrent pain and swelling in his right lower extremity for three days following withdrawal of Rivaroxaban. He was diagnosed with DVT and antithrombin III deficiency as genetic testing revealed a single nucleotide variant in SERPINC1 (c.667T>C, p.S223P). The patient was advised to accept long-term anticoagulant therapy.

CONCLUSION

Inherited AT3 deficiency due to SERPINC1 mutations results in recurrent VTE. Patients may benefit from long-term anticoagulant therapy.

Modern Aspects of Anticoagulation System Disorders Diagnosis in Children with Different Polymorphisms in Coagulation Genes. Initial Results

Background. Hemostatic system pathology is topical and poorly studied issue in pediatrics. One of the main causes of coagulation pathway disorders associated with thrombotic events is abnormality in various parts of the hemostatic system. Vascular accidents are commonly caused by anticoagulation system factors deficiency. Conventionally, thrombosis is a common event in adult patients, and there is no adequate attention to disorders of primary physiological anticoagulants system in children. More often acquired anticoagulant proteins deficiency develops in presence of various pathological conditions, especially after the past infectious diseases. All these diseases (thrombophilia, trombotic events, cardiovascular pathology, nervous system diseases, genetic diseases) can occur separately and in association with each other, plus clinical picture of coagulation events may be similar. Objective. The aim of the study is to evaluate changes in the physiological anticoagulants system in children with different pathologies who have polymorphic variants in coagulation genes and who had new coronavirus infection. Methods. The study included 33 children who had severe coronavirus infection in family clusters and had severe chronic pathology potentially associated with disorders of the coagulation system (nervous system damage, hypertrophic cardiomyopathy, hereditary monogenic syndromes, hemato-mesenchymal dysplasia syndrome). All children underwent complete examination including clinical examination, laboratory, and instrumental diagnostics. Results. Preliminary study results indicate significant incidence of polymorphic variants in coagulation genes (one third of children with various diseases from the study). Some children had decreased activity of anticoagulation system glycoproteins (from 6% to 36%) that confirmed the topicality of the examination of anticoagulation system factors deficiency and the need for further dynamic follow-up, as well as revealing of trombophilia predictors in children in selected target groups. Study on revealing anticoagulation system disorders and mutations in coagulation genes will predict the risk of thrombotic disorders. Conclusion. The obtained results have confirmed the significant role of the ongoing study for comprehensive assessment of hemostatic system disorders in children. That will allow us to optimize the approach to diagnosis and personalize the management strategy for patients with different chronic pathologies and disorders of the natural anticoagulants system. The study is currently ongoing.

Classic Thrombophilias and Thrombotic Risk Among Middle-Aged and Older Adults: A Population-Based Cohort Study

Background

Five classic thrombophilias have been recognized: factor V Leiden (rs6025), the prothrombin G20210A variant (rs1799963), and protein C, protein S, and antithrombin deficiencies. This study aimed to determine the thrombotic risk of classic thrombophilias in a cohort of middle‐aged and older adults.

Methods and Results

Factor V Leiden, prothrombin G20210A and protein‐coding variants in the PROC (protein C), PROS1 (protein S), and SERPINC1 (antithrombin) anticoagulant genes were determined in 29 387 subjects (born 1923–1950, 60% women) who participated in the Malmö Diet and Cancer study (1991–1996). The Human Gene Mutation Database was used to define 68 disease‐causing mutations. Patients were followed up from baseline until the first event of venous thromboembolism (VTE), death, or Dec 31, 2018. Carriership (n=908, 3.1%) for disease‐causing mutations in the PROC, PROS1, and SERPINC1 genes was associated with incident VTE: Hazard ratio (HR) was 1.6 (95% CI, 1.3–1.9). Variants not in Human Gene Mutation Database were not linked to VTE (HR, 1.1; 95% CI, 0.8–1.5). Heterozygosity for rs6025 and rs1799963 was associated with incident VTE: HR, 1.8 (95% CI, 1.6–2.0) and HR, 1.6 (95% CI, 1.3–2.0), respectively. The HR for carrying 1 classical thrombophilia variant was 1.7 (95% CI, 1.6–1.9). HR was 3.9 (95% CI, 3.1–5.0) for carriers of ≥2 thrombophilia variants.

Conclusions

The 5 classic thrombophilias are associated with a dose‐graded risk of VTE in middle‐aged and older adults. Disease‐causing variants in the PROC, PROS1, and SERPINC1 genes were more common than the rs1799963 variant but the conferred genetic risk was comparable with the rs6025 and rs1799963 variants.

N-Glycosylation as a Tool to Study Antithrombin Secretion, Conformation, and Function

N-linked glycosylation is a crucial post-translational modification involved in protein folding, function, and clearance. N-linked glycosylation is also used therapeutically to enhance the half-lives of many proteins. Antithrombin, a serpin with four potential N-glycosylation sites, plays a pivotal role in hemostasis, wherein its deficiency significantly increases thrombotic risk. In this study, we used the introduction of N-glycosylation sites as a tool to explore what effect this glycosylation has on the protein folding, secretion, and function of this key anticoagulant. To accomplish this task, we introduced an additional N-glycosylation sequence in each strand. Interestingly, all regions that likely fold rapidly or were surrounded by lysines were not glycosylated even though an N-glycosylation sequon was present. The new sequon in the strands of the A- and B-sheets reduced secretion, and the B-sheet was more sensitive to these changes. However, the mutations in the strands of the C-sheet allowed correct folding and secretion, which resulted in functional variants. Therefore, our study revealed crucial regions for antithrombin secretion and could potentially apply to all serpins. These results could also help us understand the functional effects of natural variants causing type-I deficiencies.

Congenital antithrombin deficiency in patients with splanchnic vein thrombosis

BACKGROUND AND AIMS

Splanchnic vein thromboses (SVT) are a rare condition that can be life-threatening. The most severe thrombophilia associated to SVT is antithrombin (AT) deficiency, usually caused by SERPINC1 mutations. Although transitory AT deficiencies and congenital disorders of the N-glycosylation pathways (CDG) have been recently reported as causes of AT deficiency, the current AT clinical screening still only includes anti-FXa activity. This study aims to (a) improve the detection of AT deficiency in SVT and (b) characterize the features of AT deficiency associated with SVT.

METHODS

The study was performed in 2 cohorts: (a) 89 SVT patients with different underlying etiologies but in whom AT deficiency had been ruled out by classical diagnostic methods; and (b) 271 unrelated patients with confirmed AT deficiency and venous thrombosis. AT was evaluated by functional (anti-FXa and anti-FIIa) and immunological methods (ELISA, crossed immunoelectrophoresis, western blot), and SERPINC1 sequencing was performed.

RESULTS

In 4/89 patients (4.5%) additional alterations in AT were found (two had SERPINC1 mutations, one had a specific variant causing transient AT deficiency and one patient had CDG). In 11 of the 271 patients (4.1%) with AT deficiency and thrombosis, thrombosis was located at the splanchnic venous territory.

CONCLUSIONS

Antithrombin deficiency may be underdiagnosed by current clinical screening techniques. Therefore, a comprehensive AT evaluation should be considered in cases of rethrombosis or doubtful interpretation of anti-FXa activity levels. SVT is a relatively common localization of the thrombotic event in patients with congenital AT deficiency.

Recommendations for clinical laboratory testing for antithrombin deficiency; Communication from the SSC of the ISTH

Hereditary deficiency of antithrombin, a natural anticoagulant, causes a thrombophilia with a high risk for venous thromboembolism. Guidance for laboratory testing to diagnose antithrombin deficiency include the use of an activity assay for initial testing, performing an antigen test and activity-to-antigen ratio when the activity level is low, using pediatric reference ranges until the age of 6 months, excluding acquired causes of low antithrombin (e.g. liver dysfunction, proteinuria, heparin, disseminated intravascular coagulation, thrombosis, surgery) or falsely normal/elevated results (e.g. argatroban, bivalirudin, dabigatran in factor IIa-based assays; rivaroxaban, apixaban, edoxaban, but not betrixaban in Xa-based assays). Molecular testing, if available, may help determine the risk for thrombosis as this might vary among the different mutations. Moreover, it will identify mutations that can be missed by traditional activity assays. Strategies for interpreting laboratory test results are provided.

Association of SERPINC1 Gene Polymorphism (rs2227589) With Pulmonary Embolism Risk in a Chinese Population

Background and Aims: Genetic variants in the gene SERPINC1 have been shown to be associated with antithrombin deficiency, which subsequently contributes to the susceptibility to venous thrombosis. However, several other studies have shown conflicting results regarding the association of SERPINC1 gene polymorphisms (rs2227589) with the risk of thrombosis. Hence, in the present study, we conducted a case-control study to further evaluate the association between the variant rs2227589 with antithrombin deficiency in pulmonary embolism (PTE). A pooled systematic analysis was also conducted to evaluate the risk of rs2227589 in venous thromboembolism (VTE) among multiple populations. Methods: This case-control study involved 101 patients and 199 healthy controls. The allele frequency of SERPINC1 variant rs2227589 was analyzed by Sequenom assay. Antithrombin anticoagulant activity was detected using an automatic coagulation analyzer. In addition, a pooled systematic analysis on 10 cohorts consisting of 5,518 patients with VTE and 8,935 controls was performed. Results: In total, 27 (26.7%) PTE subjects were diagnosed as having antithrombin deficiency. Our results showed that antithrombin plasma activity was slightly lower in T allele carriers than that in C allele carriers. However, there was no significant correlation between rs2227589 genotype and antithrombin anticoagulant activity. The recessive model showed that rs2227589 was significantly associated (p = 0.026) with an increased risk {odds ratio [OR]: 2.31, 95% confidence interval [CI] (1.09-4.89)} of Chinese PTE. The pooled systematic analysis of all case-control study and meta-analysis showed that rs2227589 polymorphism was associated with an increased risk of VTE in the additive model [OR: 1.09, 95% CI (1.01-1.18), P = 0.029] and dominant model [OR: 1.10, 95% CI (1.01-1.20), P = 0.034]. Conclusions: Our study demonstrated that variant rs2227589 is associated with an increased risk of PTE in a Chinese population but no correlation with antithrombin anticoagulant activity. However, pooled systematic analysis of multiple populations showed a significant association between rs2227589 and the risk of VTE in the additive and dominant genetic model.

A series of 10 Polish patients with thromboembolic events and antithrombin deficiency: two new c.1154-1 G>C and c.1219-534 A>G SERPINC1 gene splicing mutations

: Inherited antithrombin (AT) deficiency, with prevalence in the general population ranging 0.02-0.17%, is an autosomal dominant disorder associated with a high risk of venous thromboembolism. In most cases, deficiency is caused by mutations in the AT-coding gene (SERPINC1). Only 24 splicing defects have been described causing AT deficiency, all affecting exon flanking regions. The aim of the current study was to characterize the mutations underlying AT deficiency in 10 venous thromboembolism Polish patients aged 42.9 (14-63) years. Whole SERPINC1 gene sequencing was done by next generation sequencing methods. Eight cases had mutations previously described. However, we identified two new intronic mutations that might affect the correct splicing of exon 6 according to in-silico predictions: c.1154-1 G>C, which strongly disturbs the acceptor sequence and c.1219-534 A>G, a deep intronic mutation that might generate a cryptic donor sequence; both might compete with the wild-type donor sequence and explain the associated moderate AT deficiency of carriers. In conclusion, we show the molecular base of AT deficiency in 10 new Polish patients, including two novel SERPINC1 gene mutations potentially affecting splicing.

Management of antithrombin deficiency: an update for clinicians

Introduction. Antithrombin is a serpin that inhibits multiple procoagulant serine proteases and acts as an endogenous anticoagulant. Thus, congenital antithrombin deficiency constitutes a major thrombophilic state, the most severe so far. Areas covered. In the present work, we globally review the biology, genetics, diagnosis, and management of congenital antithrombin deficiency, and also discuss puzzling questions and future perspectives regarding this severe inherited thrombophilia. Expert opinion. Although this disorder exerts high clinical heterogeneity, many carriers will need careful and long-term anticoagulation and/or thromboprophylaxis, especially in high-risk situations, such as surgery and pregnancy. Notably, antithrombin concentrates constitute a considerable arsenal for both treatment and prevention of acute venous thrombosis in subjects with antithrombin deficiency. Current evidences are based almost exclusively on retrospective case series, so an integrated functional, biochemical and molecular characterization will be of clinical relevance and guide hematologists' personalized decisions.

To be or not to be a case of heparin resistance

Heparin resistance can be defined as high doses of unfractionated heparin (UFH), greater than 35,000 IU/day, required to raise the activated partial thromboplastin time (aPTT) and activated coagulation time (ACT) to within therapeutically desired ranges or the impossibility of doing so. The most common pathology responsible is the deficiency of anti-thrombin III (ATIII) deficiency. Other clinically relevant conditions that can present with heparin resistance are congenital deficiencies; use of high doses of heparin during extracorporeal circulation, use of asparaginase therapy and disseminated intravascular coagulation (DIC). Most of these conditions effect the ATIII levels. Patients are typically identified in an acute phase, when determination of the cause of resistance is challenging. We present a case where a patient presented with suspected heparin resistance in an acute phase of sickness, where timely intervention was able to prevent a potentially fatal situation.

Abbreviations: Neuroendocrine tumors (NETs), World health Organization (WHO), Radiation therapy (RT)

What is currently known about the genetics of venous thromboembolism at the dawn of next generation sequencing technologies

Venous thromboembolism (VTE) has a strong genetic component. This review summarizes what is known at the seventeen genes that are now well established to harbour VTE-associated genetic variants. In addition, it discusses additional candidate genes that deserve further validation before being claimed as VTE associated genes. Finally, several research strategies are briefly described to identify other molecular determinants of the disease.

Recurrent mutations in a SERPINC1 hotspot associate with venous thrombosis without apparent antithrombin deficiency

Despite the essential anticoagulant function of antithrombin and the high risk of thrombosis associated with its deficiency, the prevalence of antithrombin deficiency among patients with venous thromboembolism (VTE) is very low. However, increasing evidence suggests that antithrombin deficiency may be underestimated. The analysis of SERPINC1, the gene encoding antithrombin, in 1,304 consecutive Chinese VTE patients and 1,334 healthy controls revealed a hotspot involving residues 294 and 295 that severely increases the risk of VTE. We detected the c.883G>A (p.Val295Met) (rs201381904) mutation in 11 patients and just one control (OR = 13.6; 95% CI: 1.7-107.1); c.881G>T (p.Arg294Leu) (rs587776397) in six patients but no controls; and c.880C>T (p.Arg294Cys) (rs747142328) in two patients but no controls. In addition, c.881G>A (p.Arg294His) (rs587776397) was identified in one control. These mutations were absent in a Caucasian cohort. Carriers of these mutations had normal antithrombin levels and anticoagulant activity, consistent with results obtained in a recombinant model. However, mutation carriers had a significantly increased endogenous thrombin potential. Our results suggest the existence in the Chinese population of a hotspot in SERPINC1 that significantly increases the risk of VTE by impairing the anticoagulant capacity of the hemostatic system. This effect is not revealed by current antigen or in vitro functional antithrombin assays.

Transient desialylation in combination with a novel antithrombin deficiency causing a severe and recurrent thrombosis despite anticoagulation therapy

An in-depth focused study of specific cases of patients with recurrent thrombosis may help to identify novel circumstances, genetic and acquired factors contributing to the development of this disorder. The aim of this study was to carry out a detailed and sequential analysis of samples from a patient suffering from early and recurrent venous and arterial thrombosis. We performed thrombophilic tests, biochemical, functional, genetic and glycomic analysis of antithrombin and other plasma proteins. The patient carried a new type I antithrombin mutation (p.Ile218del), whose structural relevance was verified in a recombinant model. Experiments with N-glycosidase F and neuraminidase suggested a nearly full desialylation of plasma proteins, which was confirmed by mass spectrometry analysis of transferrin glycoforms. However, partial desialylation and normal patterns were detected in samples collected at other time-points. Desialylation was noticeable after arterial events and was associated with low antithrombin activity, reduced platelet count and glomerular filtration rate. This is the first description of a global and transient desialylation of plasma proteins associated with thrombosis. The decrease in the strong electronegative charge of terminal glycans may modulate hemostatic protein-protein interactions, which in combination with a strong prothrombotic situation, such as antithrombin deficiency, could increase the risk of thrombosis.

Thrombotic risk according to SERPINC1 genotype in a large cohort of subjects with antithrombin inherited deficiency

Inherited quantitative (type I) or qualitative (type II) antithrombin deficiency (ATD) due to mutations in the SERPINC1 gene is a well-known risk factor for venous thromboembolism. ATD may also increase risk for arterial thrombosis. Few studies have investigated risk for thrombosis according to mutations. We addressed this topic in a large retrospective cohort study of 540 heterozygous carriers of SERPINC1 mutations and compared risk for first venous or arterial thrombosis associated with carrying of different type II or type I mutations. No clear difference in risk for first venous thrombotic event was observed among type I (missense or null), type IIRS or type IIPE mutation carriers except for a few variants that displayed lower risk [all events, adjusted relative risk: Cambridge II: 0.42 (95 %CI 0.25-0.70), Dublin: 0.35 (95 %CI 0.13-0.99)]. IIHBS mutation carrying was associated with a clearly lower risk than type I mutation carrying [0.28 (95 %CI 0.20-0.40)]. These differences in risk were observed for both all venous thrombotic events and pulmonary embolism associated with deep venous thrombosis. The HBS group was also heterogeneous, with AT Budapest 3 carriers displaying a non-significantly different risk [0.61 (95 %CI 0.31-1.20)] compared to type I mutation carriers. We also studied risk for arterial thrombosis and found no significant influence of mutation type. Altogether, our findings suggest a place for SERPINC1 genotyping in the diagnosis of ATD.

High levels of latent antithrombin in plasma from patients with antithrombin deficiency

Antithrombin is an anticoagulant serpin that efficiently inhibits multiple procoagulant proteases. The cost for the structural flexibility required for this function is the vulnerability to mutations that impact its folding pathway. Most conformational mutations identified in serpins cause polymerisation. Only three mutations in SERPINC1 affecting two residues have been found to favour transformation to the latent conformation of antithrombin, another hyperstable non-anticoagulant form with strong antiangiogenic activity that constitutes 3 % of plasma antithrombin in healthy subjects. The analysis of latent antithrombin in 141 unrelated patients with antithrombin deficiency carrying 89 different SERPINC1 mutations identified four cases with higher levels than that of controls: p.Pro439Thr, p.Pro461Ser, p.Met283Val, and p.His401Tyr, the last also with circulating polymers. Heating of plasma at 42ºC exacerbated the transformation to the latent conformation in p.Pro439Thr and p.Pro461Ser. The conformational effect of p.Met283Val, the mutation associated with the highest levels of latent antithrombin detected in four members of a family, was verified in a recombinant model. Antithrombin deficiency in these cases should be classified as pleiotropic based on the impaired reactivity and low heparin affinity of the variant. Despite high levels of latent antithrombin (up to 80 µg/ml in p.Met283Val carriers), no vascular defects were described in carriers of these mutations. In conclusion, our study identifies new residues involved in the structural stability of antithrombin (and potentially of all serpins). High levels of endogenous latent antithrombin seem to play a minor antiangiogenic effect. Finally, pleiotropic deficiencies may be caused by mutations inducing transformation to the latent conformation.