Evaluation of maternal serum SERPINC1, E-selectin, P-selectin, RBP4 and PP13 levels in pregnancies complicated with preeclampsia

OBJECTIVE

The aim of this study is to investigate whether Serpin clade C (SERPINC1), E-selectin, P-selectin, Placental protein 13 (PP13), and Retinol-binding protein-4 (RBP4) levels in maternal serum were associated with the presence of preeclampsia and to compare them with uncomplicated pregnancies.

METHODS

This prospective study included 40 women with preeclampsia and 40 healthy pregnant women. An enzyme-linked immunosorbent assay kit was used to measure serum SERPINC1, E-selectin, P-selectin, PP13, and RBP4 levels.

RESULTS

The preeclampsia group had significantly higher E-selectin and P-selectin levels than the control group. PP13 and SERPINC1 levels were also significantly lower than the control group. There was no significant difference in RBP4 levels. The receiver operating characteristic curve revealed the best cutoff values for the following: E-selectin >19.2 ng/mL, with 87.5% sensitivity and 95% specificity; P-selectin >5.1 ng/mL, with 97.5% sensitivity and 100% specificity; PP13 ≤ 107.03 pg/mL, with 72.5% sensitivity and 77.5% specificity; and SERPINC1 ≤ 87.76 ng/mL, with 100% sensitivity and 97.5% specificity.

CONCLUSION

In this study, the endothelial dysfunction parameters SERPINC1, PP13, E-selectin, and P-selectin were found to be associated with preeclampsia. Endothelial dysfunction biomarkers in maternal non-serum body fluids may differ. More research is needed, especially to determine the relationship between SERPINC1 and preeclampsia.

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.

Assessment of maternal serum SERPINC1, E-selectin, P-selectin, and RBP4 levels in pregnancies with early- and late-onset preeclampsia

INTRODUCTION

To investigate whether the SERPINC1, E-selectin, P-selectin, and RBP4 levels in first trimester maternal serum was associated with the presence of preeclampsia (PE).

METHODS

This cross-sectional study was conducted on 26 women with early-onset preeclampsia (EO-PE), 27 women with late-onset preeclampsia (LO-PE), and 27 women with uncomplicated pregnancies. Levels of serum SERPINC1, E-selectin, P-selectin, and RBP4 were measured with the use of an enzyme-linked immunosorbent assay (ELISA) kit.

RESULTS

E-Selectin levels in patients with EO-PE were higher than those with LO-PE and control patients (p_E-L  = 0.025; p_E-C  = 0.000; p < 0.05). There was no significant intergroup difference in terms of P-selectin and RBP4 levels (p > 0.05). SERPINC1 levels were lower in the patients in the with EO-PE group than in those in the LO-PE and the control groups (p_E-L  = 0.000; p_E-C  = 0.000; p < 0.05). In the PE group, there was a negative, moderate (41.7%) correlation between E-selectin level and SERPINC1 (p = 0.002; p < 0.05). The receiver operating characteristic (ROC) curve showed that the best cut-off values for E-selectin were 23.14 ng/ml > with 100% sensitivity and 100% specificity. The ROC curve showed that the best cut-off values for SERPINC1 were ≤87.76 ng/ml with 98.1% sensitivity and 96.3% specificity.

DISCUSSION

Of the endothelial damage parameters, E-selectin and SERPINC1 are especially associated with EO-PE. Furthermore, they can be used as potential early diagnosis markers in the prediction of PE.

Identification and characterization of two SERPINC1 mutations causing congenital antithrombin deficiency

BACKGROUND

Antithrombin (AT) is the main physiological anticoagulant involved in hemostasis. Hereditary AT deficiency is a rare autosomal dominant thrombotic disease mainly caused by mutations in SERPINC1, which was usually manifested as venous thrombosis and pulmonary embolism. In this study, we analyzed the clinical characteristics and screened for mutant genes in two pedigrees with hereditary AT deficiency, and the functional effects of the pathogenic mutations were evaluated.

METHODS

Candidate gene variants were analyzed by next-generation sequencing to screen pathogenic mutations in probands, followed by segregation analysis in families by Sanger sequencing. Mutant and wild-type plasmids were constructed and transfected into HEK293T cells to observe protein expression and cellular localization of SERPINC1. The structure and function of the mutations were analyzed by bioinformatic analyses.

RESULTS

The proband of pedigree A with AT deficiency carried a heterozygous frameshift mutation c.1377delC (p.Asn460Thrfs*20) in SERPINC1 (NM000488.3), a 1377C base deletion in exon 7 resulting in a backward shift of the open reading frame, with termination after translation of 20 residues, and a different residue sequence translated after the frameshift. Bioinformatics analysis suggests that the missing amino acid sequence caused by the frameshift mutation might disrupt the disulfide bond between Cys279 and Cys462 and affect the structural function of the protein. This newly discovered variant is not currently included in the ClinVar and HGMD databases. p.Arg229* resulted in a premature stop codon in exon 4, and bioinformatics analysis suggests that the truncated protein structure lost its domain of interaction with factor IX (Ala414 site) after the deletion of nonsense mutations. However, considering the AT truncation protein resulting from the p.Arg229* variant loss a great proportion of the molecule, we speculate the variant may affect two functional domains HBS and RCL and lack of the corresponding function. The thrombophilia and decreased-AT-activity phenotypes of the two pedigrees were separated from their genetic variants. After lentiviral plasmid transfection into HEK293T cells, the expression level of AT protein decreased in the constructed c.1377delC mutant cells compared to that in the wild-type, which was not only reduced in c.685C > T mutant cells but also showed a significant band at 35 kDa, suggesting a truncated protein. Immunofluorescence localization showed no significant differences in protein localization before and after the mutation.

CONCLUSIONS

The p.Asn460Thrfs*20 and p.Arg229* variants of SERPINC1 were responsible for the two hereditary AT deficiency pedigrees, which led to AT deficiency by different mechanisms. The p.Asn460Thrfs*20 variant is reported for the first time.

Favourable outcome of multisystem venous thrombosis associated with novel SERPINC1 mutation after treated with dabigatran: a case report with 7-year follow-up

BACKGROUND

Mutations in SERPINC1 lead to deficiency in antithrombin (AT) which is an endogenous anticoagulant of normal hemostasis and could result in venous thromboembolism (VTE).

CASE PRESENTATION

A 61-year-old male patient with recurrent thrombosis returned to the hospital with multiple cerebral thrombosis after voluntary cessation of dabigatran therapy. Laboratory tests revealed a type I AT deficiency in this patient and further whole exome sequencing (WES) identified a novel heterozygous frameshift duplication (c.233_236dup, p.Val80Alafs*26) in SERPINC1 gene. Long-term dabigatran treatment was given and no recurrence or side effects were found within the followed 5 years.

CONCLUSION

A multisystem VTE patient with a novel SERPINC1 mutation (c.233_236dup, p.Val80Alafs*26) reached a favourable outcome after dabigatran treatment.

Native and activated antithrombin inhibits TMPRSS2 activity and SARS-CoV-2 infection

Host cell proteases such as TMPRSS2 are critical determinants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) tropism and pathogenesis. Here, we show that antithrombin (AT), an endogenous serine protease inhibitor regulating coagulation, is a broad-spectrum inhibitor of coronavirus infection. Molecular docking and enzyme activity assays demonstrate that AT binds and inhibits TMPRSS2, a serine protease that primes the Spike proteins of coronaviruses for subsequent fusion. Consequently, AT blocks entry driven by the Spikes of SARS-CoV, MERS-CoV, hCoV-229E, SARS-CoV-2 and its variants of concern including Omicron, and suppresses lung cell infection with genuine SARS-CoV-2. Thus, AT is an endogenous inhibitor of SARS-CoV-2 that may be involved in COVID-19 pathogenesis. We further demonstrate that activation of AT by anticoagulants, such as heparin or fondaparinux, increases the anti-TMPRSS2 and anti-SARS-CoV-2 activity of AT, suggesting that repurposing of native and activated AT for COVID-19 treatment should be explored.

Genetic Analysis of a Pedigree With Antithrombin and Prothrombin Compound Mutations and Antithrombin Heterozygotes

Background and Aims: Antithrombin (AT) is the most important physiological inhibitor in vivo, and coagulation factor II (FII) or prothrombin is a coagulation factor vital to life. The purpose of our research was to illustrate the connection between gene mutations and the corresponding deficiencies of AT and FII.

Methods: Functional and molecular analyses were performed. The possible impact of the mutation was analyzed by online bioinformatics software. ClustalX-2.1-win and PyMol/Swiss-Pdb Viewer software were used for conservative analyses and to generate molecular graphic images, respectively.

Results: The proband showed a lower limb venous thrombosis and acute pulmonary embolism infarction with reduced AT activity (50%). His mother, with subcutaneous ecchymosis, had reduced activities of AT and FII, of 44 and 5%, respectively. Molecular analysis showed that both the proband and his mother carried c.964A > T (p.Lys322stop) heterozygotes in SERPINC1. The difference was that his mother carried homozygous c.494C > T (p.Thr165Met) in F2, while the proband was wild type. Bioinformatics and model analysis indicated that mutations may destroy the function and structure of AT and FII protein.

Conclusion: This study identified a novel mutation of SERPINC1 and a missense mutation of F2, which may be the molecular mechanism leading to AT and FII deficiency in this family. It will help genetic diagnosis and counseling for thrombotic families.

Downregulation of microRNA-200c-3p alleviates the aggravation of venous thromboembolism by targeting serpin family C member 1

Venous thromboembolism (VTE) is the third most prevalent cardiovascular complication. Increasing studies have demonstrated that some microRNAs (miRNAs) are aberrantly expressed in VTE and play crucial roles in mediating the development of VTE. Therefore, our study intends to explore the detailed function and molecular mechanism of miR-200c-3p in VTE progression. In our research, VTE rat models were first established via inferior vena cava (IVC) ligation and the time-dependent effects of IVC ligation on thrombus formation were discovered. The results of reverse transcription quantitative polymerase-chain reaction (RT-qPCR) and western blotting showed that serpin family C member 1 (SERPINC1) was downregulated in VTE rat models and showed an inverse correlation with thrombus load. MiRNA target prediction tools and luciferase reporter assay confirmed SERPINC1 as a target for miR-200c-3p. VTE rats were injected with miR-200c-3p inhibitor for 24 h to investigate whether miR-200c-3p knockdown influences thrombus formation in vivo. Histological examination through hematoxylin-eosin staining revealed that miR-200c-3p downregulation markedly inhibited the formation of thrombus in IVC of rats. Additionally, miR-200c-3p was upregulated while SERPINC1 was downregulated in serum and inferior vena cava of VTE rats as well as in plasma of patients with VTE. Linear regression analysis demonstrated that miR-200c-3p expression was negatively correlated to SERPINC1 expression in VTE rats and patients with VTE. Our study determines the previously unelucidated function of miR-200c-3p in VTE, which might provide a potential novel insight for the treatment of VTE.

The Higher Prevalence of Venous Thromboembolism in the Hungarian Roma Population Could Be Due to Elevated Genetic Risk and Stronger Gene-Environmental Interactions

Background: Interactions between genetic and environmental risk factors (GxE) contribute to an increased risk of venous thromboembolism (VTE). Understanding how these factors interact provides insight for the early identification of at-risk groups within a population and creates an opportunity to apply appropriate preventive and curative measures.

Objective: To estimate and compare GxE for VTE risk in the general Hungarian and Roma populations.

Methods: The study was based on data extracted from a database consisting of results previously obtained from a complex health survey with three pillars (questionnaire-based, physical, and laboratory examinations) involving 406 general Hungarian and 395 Roma subjects. DNA was genotyped for rs121909567 (SERPINC1), rs1799963 (F2), rs2036914 (F11), rs2066865 (FGG), rs6025 (F5), and rs8176719 (ABO) polymorphisms. After allele frequency comparisons, the odds ratio (OR) was calculated for individual SNPs. Furthermore, genetic risk scores (weighted GRS, unweighted GRS) were computed to estimate the joint effect of the genetic factors. Multivariable linear regression analysis was applied to test the impact of GxE on VTE risk after interaction terms were created between genetic and VTE risk factors [diabetes mellitus (DM), cancer, chronic kidney diseases (CKD), coronary artery diseases (CAD), migraine, depression, obesity, total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), high density lipoprotein (HDL-C), triglyceride (TG), and smoking].

Results: Interestingly, the rs121909567 (SERPINC1, ATBp3 mutation) SNP was not present in the general population at all. However, the risk allele frequency was 1% among the Roma population, which might suggest a founder effect in this minority. This polymorphism multiplicatively interacted with CAD, CKD, cancer, DM, depression, migraine, and obesity. Even though interactions were not statistically significant, the trend of interaction showed the probability of an incremental VTE risk among the Roma population. The risk of VTE was 4.7 times higher (p > 0.05) for Roma subjects who had ≥3 wGRS (median value) compared with individuals having lower wGRS values but lower for the general subjects (OR = 3.1 × 10⁻⁸). Additionally, the risk of VTE was 6.6 times higher in the Roma population that had ≥3 risk alleles (median value) than in individuals with the 0–1 risk allele, and the overall risk was much higher for the Roma population (OR = 6.6; p > 0.05) than for the general Hungarian population (OR = 1.5; p > 0.05). Five positive and significant GxE interactions were identified in the Roma population. The risk of VTE was higher among depressive Roma subjects who carried the risk variant rs2036914 (β = 0.819, p = 0.02); however, this interaction was not significant for the general subjects. The joint presence of high levels of LDL-C and rs2066865 (FGG) increased the VTE risk only among Roma individuals (β = 0.389, p = 0.002). The possibility of VTE risk increment, as a result of a multiplicative interaction between rs8176719 (ABO) and cancer, was identified, which was higher for the Roma population (β = 0.370, p < 0.001) than for the general population (β = −0.042, p = 0.6). The VTE risk increased in the Roma population (β = 0.280, p = 0.001), but was higher in the general population (β = 0.423, p = 0.001) as a result of the multiplicative interaction between CAD and rs2036914 (F11). The presence of a multiplicative interaction between rs2066865 (FGG) and CAD increased the VTE risk for the Roma population (β = 0.143, p = 0.046) but not for the general population (β = −0.329, p < 0.001).

Conclusions: rs121909567 (SERPINC1, ATBp3) was confirmed as a founder mutation in the Roma population. Our study revealed some evidence on the burden of the joint presence of genetic and environmental risk factors on VTE, although the finding is highly subjected to the selection and observational biases due to the very small number of VTE cases and the observational nature of the study design, respectively. As a result of higher genetic load and GxE interactions, this minority Roma population is at higher risk of VTE than the general Hungarian population. Thus, our results suggest the need for an intensive search for the rs121909567 (SERPINC1; ATBp3) founder mutation, which might be an important factor for the assessment of thrombotic disease susceptibility among the Roma population. In addition, we strongly recommend further studies among a large number of VTE cases to explore the more precise impact of genetic and environmental risk factors on VTE in the study populations.

Cis-Segregation of c.1171C>T Stop Codon (p.R391*) in SERPINC1 Gene and c.1691G>A Transition (p.R506Q) in F5 Gene and Selected GWAS Multilocus Approach in Inherited Thrombophilia

Inherited thrombophilia (e.g., venous thromboembolism, VTE) is due to rare loss-of-function mutations in anticoagulant factors genes (i.e., SERPINC1, PROC, PROS1), common gain-of-function mutations in procoagulant factors genes (i.e., F5, F2), and acquired risk conditions. Genome Wide Association Studies (GWAS) recently recognized several genes associated with VTE though gene defects may unpredictably remain asymptomatic, so calculating the individual genetic predisposition is a challenging task. We investigated a large family with severe, recurrent, early-onset VTE in which two sisters experienced VTE during pregnancies characterized by a perinatal in-utero thrombosis in the newborn and a life-saving pregnancy-interruption because of massive VTE, respectively. A nonsense mutation (CGA > TGA) generating a premature stop-codon (c.1171C>T; p.R391*) in the exon 6 of SERPINC1 gene (1q25.1) causing Antithrombin (AT) deficiency and the common missense mutation (c.1691G>A; p.R506Q) in the exon 10 of F5 gene (1q24.2) (i.e., FV Leiden; rs6025) were coinherited in all the symptomatic members investigated suspecting a cis-segregation further confirmed by STR-linkage-analyses [i.e., SERPINC1 IVS5 (ATT)_5–18, F5 IVS2 (AT)_6–33 and F5 IVS11 (GT)_12–16] and SERPINC1 intragenic variants (i.e., rs5878 and rs677). A multilocus investigation of blood-coagulation balance genes detected the coexistence of FV Leiden (rs6025) in trans with FV HR2-haplotype (p.H1299R; rs1800595) in the aborted fetus, and F11 rs2289252, F12 rs1801020, F13A1 rs5985, and KNG1 rs710446 in the newborn and other members. Common selected gene variants may strongly synergize with less common mutations tuning potential life-threatening conditions when combined with rare severest mutations. Merging classic and newly GWAS-identified gene markers in at risk families is mandatory for VTE risk estimation in the clinical practice, avoiding partial risk score evaluation in unrecognized at risk patients.

Novel SERPINC1 missense mutation (Cys462Tyr) causes disruption of the 279Cys-462Cys disulfide bond and leads to type Ⅰ hereditary antithrombin deficiency

BACKGROUND

Antithrombin (AT) is the primary physiological anticoagulant of normal hemostasis. Hereditary AT deficiency, an autosomal dominant thrombotic disease caused by mutations in the AT gene (SERPINC1), is associated with venous thromboembolism.

OBJECTIVE

We investigated the phenotypes, genotypes, and pathogenesis of hereditary AT deficiency in a 12-year-old boy (proband) who developed a pulmonary embolism and a subsequent deep vein thrombosis.

METHODS

The AT activity and AT antigen level of the proband and his family members were measured. Mutation sites in all seven exons of SERPINC1 were identified. Analysis of conserved regions around codon 462 of the SERPINC1 gene and functional predictions were performed using bioinformatics tools.

RESULTS

The proband, his father, and his paternal grandmother demonstrated reduced AT activity and antigen levels consistent with Type I AT deficiency. A novel heterozygous missense mutation, c.1385G>A (Cys462Tyr) was identified in all three symptomatic family members. This missense mutation causes disruption of the 279Cys-462Cys disulfide bond and leads to type Ⅰ hereditary AT deficiency.

CONCLUSION

A SERPINC1 missense mutation (Cys462Tyr) causing damage to the 279Cys-462Cys disulfide bond of the AT protein appears to be the cause of Type I AT deficiency in this family. These findings indicate one pathological mechanism associated with hereditary AT deficiency.

New genetic variant in the SERPINC1 gene: hereditary Antithrombin deficiency case report, familial thrombosis and considerations on genetic counseling

BACKGROUND

Inherited deficiency of the antithrombin (hereditary antithrombin deficiency, AT deficiency, OMIM #613118) is a relatively rare (1:2000-3000) autosomal-dominant disorder with high risk of venous thromboembolism. Mutations in the serpin family C member 1 gene (SERPINC1) can lead to Quantitative (type I) and Qualitative (type II) types of antithrombin deficiency. We describe a new genetic variant in the SERPINC1 gene and our approach to variant interpretation.

CASE PRESENTATION

We observed a 29 y.o. female proband with the episode of venous thrombosis at the age of 18 and family history of thrombosis. The antithrombin level in our patient was low, 44-48% (AT deficiency type I). A new genetic variant c.662G > C (p.W221S) in the SERPINC1 gene was detected in proband and affected father but was absent in healthy sister. We used in silico tools to evaluate the possible impact of p.W221S variant on protein structure and function. In mutated SERPINC1 protein a new N-linked glycosylation site is formed, however, it is unclear if the glycosylation at 219-221 site is possible.

CONCLUSION

The proband was provided with appropriate genetic counseling and referred to a hematologist. Based on all the evidence we classify the p.W221S variant as variant of unknown clinical significance. In this paper we discuss some aspects of genetic counseling, variant interpretation and thromboembolic prophilaxis.

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.

Two Novel Mutations Cause Hereditary Antithrombin Deficiency in a Chinese Family

OBJECTIVE

To study the molecular basis of hereditary antithrombin (AT) deficiency in a Chinese family. It will help us understand the pathogenesis of this type of disease.

METHOD

AT activity (AT:A) and the AT antigen (AT:Ag) level were tested by chromogenic substrate and immunoturbidimetry, respectively. To identify the novel mutations, SERPINC1 gene sequencing was carried out. The possible impact of the mutations was analyzed by model and bioinformatic analyses.

RESULTS

AT:A and the AT:Ag level of the proband were 43% and 113 mg/L (normal range: 98-119% and 250-360 mg/L), respectively. Sequencing analysis revealed compound heterozygous mutations, including a frameshift mutation (c.318_319insT) resulting in Asn75stop and a missense mutation (c.922G>T) resulting in Gly276Cys. The bioinformatic and model analyses indicated that these mutations may disrupt the function and structure of the AT protein.

CONCLUSION

We detected 2 novel heterozygous mutations (c.318_319insT and c.922G>T) in the proband, and these were associated with decreased AT:A.

Molecular basis of SERPINC1 mutations in Japanese patients with antithrombin deficiency

BACKGROUND

Congenital antithrombin (AT) deficiency, which arises from various SERPINC1 defects, is an autosomal-dominant thrombophilic disorder associated with a high risk of recurrent venous thromboembolism.

PATIENTS/METHODS

We investigated SERPINC1 defects in Japanese patients with congenital AT deficiency who developed venous thromboembolism or had a family history of deep vein thrombosis. We analyzed the full DNA sequences of SERPINC1 exons and exon-intron junctions by PCR-mediated direct sequencing. If no mutation was found, multiplex ligation-dependent probe amplification (MLPA) was conducted for the relative quantification of the copy number of all exons in SERPINC1. If splice-site mutations were detected, mRNA splicing abnormalities were further investigated using an in vitro cell-based exontrap assay.

RESULTS

We identified 19 different SERPINC1 abnormalities, including 8 novel mutations, in 21 Japanese patients with AT deficiency. These abnormalities were distributed as follows: 9 missense mutations (42.9%), 3 nonsense mutations (14.3%), 1 splice-site mutation (4.8%), 2 small insertions (9.5%), 2 deletion mutations (9.5%) and 4 large deletions (19.0%). Cases with large deletions of SERPINC1 included Alu-mediated gene rearrangements and non-Alu-mediated complex gene rearrangements; the latter could conceivably be explained using the fork stalling and template switching (FoSTeS) model.

CONCLUSIONS

We identified a variety of SERPINC1 defects in Japanese patients with AT deficiency. The SERPINC1 mutations detected in patients with type I AT deficiency included single nucleotide missense or nonsense mutations, small intragenic insertions or deletions, and large genomic structural deletions. Large deletions of SERPINC1 were caused by various recurrent or non-recurrent complex genomic rearrangement mutations.

SERPINC1 variants causing hereditary antithrombin deficiency in a Danish population

INTRODUCTION

Antithrombin deficiency is associated with increased risk of venous thromboembolism (VTE). We aimed to identify variants causing antithrombin deficiency in a Danish population.

MATERIALS AND METHODS

We performed Sanger sequencing and, in relevant cases, multiplex ligation-dependent probe amplification analyses, in 46 individuals (23 index cases) with and 9 relatives without antithrombin deficiency. Furthermore, in order to explore whether a combination of antithrombin type II heparin binding site (HBS) deficiency and factor V Leiden single nucleotide variant (SNV) conferred a higher risk of VTE than either risk factor alone, we performed genotyping for factor V Leiden in most of the carriers of type II HBS deficiency (n = 25).

RESULTS

We detected causal variants in all 46 carriers: three large and two small deletions, all causing type I antithrombin deficiency, and seven SNVs: one causing type I, one causing type II reactive site (RS), four causing type II HBS and one causing pleiotropic effect (PE) type II antithrombin deficiency. None of the relatives without antithrombin deficiency had the family variant. All detected SNVs have been reported previously. Majority (n = 27) of carriers had type II HBS deficiency, most often caused by the p.(Pro73Leu) SNV (n = 19). Heterozygosity for factor V Leiden was observed in three (3/25 = 12%) carriers of type II HBS deficiency. Only four (4/25 = 16%) carriers of type II HBS antithrombin deficiency experienced VTE, and two of these were heterozygous for factor V Leiden.

CONCLUSIONS

In a systematic search to identify variants causing hereditary antithrombin deficiency in a Danish population, we achieved a variant detection rate of 100%.

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.

SERPINC1 gene mutations in antithrombin deficiency

Existing evidence suggests that in most cases antithrombin deficiency can be explained by mutations in its gene, SERPINC1. We investigated the molecular background of antithrombin deficiency in a single centre family cohort study. We included a total of 21 families comprising 15 original probands and sixty-six relatives, 6 of who were surrogate probands for the genetic analysis. Antithrombin activity and antigen levels were measured. The heparin-antithrombin binding ratio assay was used to distinguish between the different subtypes of type II antithrombin deficiency. SERPINC1 mutations were detected by direct sequencing of all 7 exons and regulatory regions, and multiplex ligation-dependent probe amplification. Eighty-six per cent of the families had a detrimental SERPINC1 gene mutation that segregated in the family. We detected 13 different SERPINC1 gene mutations of which 5 were novel. Among all these mutations, 44% was associated with type I deficiency, whereas the remainder was associated with type II heparin binding site (11%), type II pleiotropic effect (33%), type II reactive site (6%) or had the antithrombin Cambridge II mutation (6%). The current study reports several novel SERPINC1 mutations, thereby adding to our knowledge of the molecular background of antithrombin deficiency. Finally, our results point out the importance of future research outside the conventional SERPINC1 gene approach.

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.

A small deletion in SERPINC1 causes type I antithrombin deficiency by promoting endoplasmic reticulum stress

Antithrombin (AT) deficiency is an autosomal dominant disorder, and identification of mutation AT variants would improve our understanding of the anticoagulant function of this serine protease inhibitor (SERPIN) and the molecular pathways underlying this disorder. In the present study, we performed whole-exome sequencing of a Chinese family with deep vein thrombosis, and identified a new small deletion that eliminates four amino acids (INEL) from exon 4 of SERPINC1 gene. This causes type I AT deficiency by enhancing the intracellular retention of this protein. AT retention leads to endoplasmic reticulum (ER) stress, which further inhibits AT release. In addition, ER stress activates ER-associated degradation, which promotes AT degradation. Suppression of ER stress enhanced the secretion of AT, while inhibition of ER-associated degradation suppressed AT release. Thus, our study identified a new mutation (INEL deletion) causing type I AT deficiency, and uncovered a novel mechanism for AT retention through enhanced ER stress, which may provide an innovative approach for treating AT deficiency.

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

The key haemostatic role of antithrombin and the risk of thrombosis associated with its deficiency support that the low incidence of antithrombin deficiency among patients with thrombosis might be explained by underestimation of this disorder. It was our aim to identify mutations in SERPINC1 causing transient antithrombin deficiency. SERPINC1 was sequenced in 214 cases with a positive test for antithrombin deficiency, including 67 with no deficiency in the sample delivered to our laboratory. The p.Val30Glu mutation (Antithrombin Dublin) was identified in five out of these 67 cases, as well as in three out of 127 cases with other SERPINC1 mutations. Genotyping in 1593 patients with venous thrombosis and 2592 controls from two populations, revealed a low prevalent polymorphism (0.3 %) that moderately increased the risk of venous thrombosis (OR: 2.9; 95 % CI: 1.07-8.09; p= 0.03) and identified one homozygous patient with an early thrombotic event. Carriers had normal anti-FXa activity, and plasma antithrombin was not sensitive to heat stress or proteolytic cleavage. Analysis of one sample with transient deficit revealed a type I deficiency, without aberrant or increased latent forms. The recombinant variant, which lacked the two amino-terminal residues, had reduced secretion from HEK-EBNA cells, formed hyperstable disulphide-linked polymers, and had negligible activity. In conclusion, p.Val30Glu by affecting the cleavage of antithrombin's signal peptide, results in a mature protein lacking the N-terminal dipeptide with no functional consequences in normal conditions, but that increases the sensitivity to be folded intracellularly into polymers, facilitating transient antithrombin deficiency and the subsequent risk of thrombosis.

Impact of the type of SERPINC1 mutation and subtype of antithrombin deficiency on the thrombotic phenotype in hereditary antithrombin deficiency

Mutations in the antithrombin (AT) gene can impair the capacity of AT to bind heparin (AT deficiency type IIHBS), its target proteases such as thrombin (type IIRS), or both (type IIPE). Type II AT deficiencies are almost exclusively caused by missense mutations, whereas type I AT deficiency can originate from missense or null mutations. In a retrospective cohort study, we investigated the impact of the type of mutation and type of AT deficiency on the manifestation of thromboembolic events in 377 patients with hereditary AT deficiencies (133 from our own cohort, 244 reported in the literature). Carriers of missense mutations showed a lower risk of venous thromboembolism (VTE) than those of null mutations (adjusted hazard ratio [HR] 0.39, 95% confidence interval [CI] 0.27-0.58, p<0.001), and the risk of VTE was significantly decreased among patients with type IIHBS AT deficiency compared to patients with other types of AT deficiency (HR 0.23, 95%CI 0.13-0.41, p<0.001). The risk of pulmonary embolism complicating deep-vein thrombosis was lower in all type II AT deficiencies compared to type I AT deficiency (relative risk 0.69, 95%CI 0.56-0.84). By contrast, the risk of arterial thromboembolism tended to be higher in carriers of missense mutations than in those with null mutations (HR 6.08-fold, 95%CI 0.74-49.81, p=0.093) and was 5.9-fold increased (95%CI 1.22-28.62, p=0.028) in type IIHBS versus other types of AT deficiency. Our data indicate that the type of inherited AT defect modulates not only the risk of thromboembolism but also the localisation and encourage further studies to unravel this phenomenon.

Molecular basis and thrombotic manifestations of antithrombin deficiency in 15 unrelated Chinese patients

INTRODUCTION

Antithrombin (AT) deficiency is associated with an increasing risk of thrombosis.

MATERIALS AND METHODS

15 unrelated patients with AT deficiency defined by thrombophilic assays were recruited and detailed clinical information about patients, focusing on the personal and family history of thromboembolism (TE), were recorded. Mutation analysis was performed by direct sequencing of an AT gene (SERPINC1) in the patients and their family members.

RESULTS

A total of 15 heterozygous causative mutations, each being identified in one family, were identified. Five mutations (33.3%) were reported here for the first time, including three null mutations (Ser36X, Lys70X and Try307X) and two missense mutations (Phe123Cys and Leu340Phe) probably impairing the structural integrity and stability of protein based on the AT structural analysis. Of the 15 patients, 33.3% (5/15) had additional risk factors and only one patient presented with additional genetic alteration causing an early onset of thrombosis. Fourteen patients (93.9%) suffered from multisite recurrent thrombotic episodes after a first episode of thrombosis. 93.3% of the patients experienced deep vein thrombosis (DVT) and 40.0% presented with mesenteric venous thrombosis (MVT). In addition, both venous and arterial thrombosis was present in two unrelated patients. 51.0% subjects with AT deficiency in the 15 unrelated pedigrees experienced TE events.

CONCLUSIONS

Prophylactic anticoagulation may be suggested in AT-deficient patients to avoid the recurrent and multisite thrombosis. The association of primary MVT and AT deficiency is highlighted.