PROC c.574_576del polymorphism: a common genetic risk factor for venous thrombosis in the Chinese population

Thrombophilia Screening: Not So Straightforward

Although inherited thrombophilias are lifelong risk factors for a first thrombotic episode, progression to thrombosis is multifactorial and not all individuals with inherited thrombophilia develop thrombosis in their lifetimes. Consequently, indiscriminate screening in patients with idiopathic thrombosis is not recommended, since presence of a thrombophilia does not necessarily predict recurrence or influence management, and testing should be selective. It follows that a decision to undertake laboratory detection of thrombophilia should be aligned with a concerted effort to identify any significant abnormalities, because it will inform patient management. Deficiencies of antithrombin and protein C are rare and usually determined using phenotypic assays assessing biological activities, whereas protein S deficiency (also rare) is commonly detected with antigenic assays for the free form of protein S since available activity assays are considered to lack specificity. In each case, no single phenotypic assay is capable of detecting every deficiency, because the various mutations express different molecular characteristics, rendering thrombophilia screening repertoires employing one assay per potential deficiency, of limited effectiveness. Activated protein C resistance (APCR) is more common than discrete deficiencies of antithrombin, protein C, and protein S and also often detected initially with phenotypic assays; however, some centres perform only genetic analysis for factor V Leiden, as this is responsible for most cases of hereditary APCR, accepting that acquired APCR and rare F5 mutations conferring APCR will go undetected if only factor V Leiden is evaluated. All phenotypic assays have interferences and limitations, which must be factored into decisions about if, and when, to test, and be given consideration in the laboratory during assay performance and interpretation. This review looks in detail at performance and limitations of routine phenotypic thrombophilia assays.

The clinical and genetic landscape of early-onset thrombophilia in Japan

OBJECTIVES

To determine the optimal management for early-onset thrombophilia (EOT), the genetic and clinical features of protein C (PC)-, protein S (PS)-, or antithrombin (AT)-deficient patients of ≤20 years of age were studied in Japan.

METHODS/RESULTS

Clinical and genetic information of all genetically diagnosed cases was collected through the prospective, retrospective study, and literature review. One-hundred-one patients had PC (n = 55), PS (n = 29), or AT deficiency (n = 18). One overlapping case had PC- and PS-monoallelic variant. Fifty-five PC-deficient patients (54%) had 26 monoallelic or 29 biallelic variant(s), and 29 (29%) PS-deficient patients had 20 monoallelic or nine biallelic variant(s). None of the patients had AT-biallelic variants. The frequent low-risk allele p.K193del (PC-Tottori) was found in five patients with monoallelic (19%) but not 29 with biallelic variant(s). The most common low-risk allele p.K196E (PS-Tokushima) was found in five with monoallelic (25%) and six with biallelic variant(s) (67%). One exceptional de novo PC variant was found in 32 families with EOT. Only five parents had a history of thromboembolism. Thrombosis concurrently developed in three mother-newborn pairs (two PC deficiency and one AT deficiency). The prospective cohort revealed the outcomes of 35 patients: three deaths with PC deficiency and 20 complication-free survivors. Neurological complications were more frequently found in patients with PC-biallelic variants than those with PC-, PS-, or AT-monoallelic variants (73% vs. 24%, p = .019).

CONCLUSIONS

We demonstrate the need for elective screening for EOT targeting PC deficiency in Japan. Early prenatal diagnosis of PC deficiency in mother-infant pairs may prevent perinatal thrombosis in them.

Analysis of PROC mutations and clinical features in 22 unrelated families with inherited protein C deficiency

Currently, limited information is available in the literature regarding the relationships between PROC mutations and clinical features in Chinese individuals. We aimed to characterize severe congenital Protein C deficiency in 22 unrelated Chinese families in a tertiary hospital by analyzing its clinical manifestation, associated risk factors, and gene mutations. We measured protein C activity and antigen levels for all participants, screened them for mutations in the PROC gene, and analyzed the clinical features of each family to identify commonalities and differences. The analysis revealed a total of 75 individuals with PCD and 16 different PROC mutations, including 12 missense mutations and 4 deletion mutations. Among them, 11 who were compound heterozygotes or homozygotes for mutations tended to develop symptoms at a younger age without any clear triggers. In contrast, the remaining 64 individuals who were heterozygotes for mutations often had clear triggers for their symptoms and experienced a milder course of the disease. It is worth noting that the mutation c.565C > T occurred most frequently, being identified in 8 out of 22 families (36%). Our team also reported five novel mutations, including c.742-744delAAG, c.383G > A, c.997G > A, c.1318C > T, and c.833T > C mutations. The identification of five novel mutations adds to the richness of the Human Genome Database. Asymptomatic heterozygotes are not uncommon, and they are prone to develop symptoms with obvious triggers. The evidence presented strongly suggest that asymptomatic individuals with family history of protein C deficiency can benefit from mutational analysis of PROC gene.

Construction and optimization of a polygenic risk model for venous thromboembolism in the Chinese population

BACKGROUND

Venous thromboembolism (VTE) has both environmental and genetic risk factors. It is regulated by polygenes and multisites. The polygenic risk score (PRS) has been widely used because any single genetic biomarker failed to accurately predict the genetic risk of VTE. However, no polygenic risk model has been proposed for VTE in the Chinese population. Thus, we aimed to construct a PRS model for the first episode of VTE in the Chinese population.

METHODS

First, single nucleotide polymorphisms (SNPs) associated with VTE in genome-wide association studies, meta-analyses, and candidate gene studies were screened as variables for the PRS. The logarithm of the odds ratio was used to weight the variables. Second, a training set with simulated data from 1000 cases of VTE and 1000 controls was created with different genotypes and frequencies. Finally, we calculated the area under the receiver operating characteristic curve (AUC) to evaluate the discriminatory ability of the PRS model.

RESULTS

We screened 53 SNPs potentially associated with the first episode of VTE in the Chinese population. The AUC of the PRS-53 model (containing 53 SNPs) was 0.748 (95% confidence interval, 0.727-0.770) in the training set. From the largest weight to the smallest weight, SNPs were incrementally added to the model to calculate the AUC for model optimization. The AUC of the PRS-10 model (containing 10 SNPs) was 0.718 (95% confidence interval, 0.696-0.740), with no statistically significant difference from the AUC for the PRS-53 model.

CONCLUSIONS

The PRS-10 and PRS-53 models showed similar predictive abilities and satisfactory discriminatory power and can be used to predict the genetic risk of the first episode of VTE in the Chinese population. The simplified PRS-10 model is more efficient in clinical practice.

Whole exome sequencing reveal 83 novel Mendelian disorders carrier P/LP variants in Chinese adult patients

Carrier screening can identify people at risk of conceiving pregnancies affected with inherited genetic disorders or who have a genetic disorder with late or variable onset. Carrier screening based on whole exome sequencing (WES) data can offer more comprehensive assessment than on-target carrier screening tests. A total of 224 Chinese adult patients WES data was analyzed, except positive variants associated with the patients' major complaint, 378 pathogenic (P) and "likely pathogenic" (LP) variants from 175 adult patients were identified. Whole exome-wide frequency of carriers for Mendelian disorders in Chinese adult patients was about 78.13% in this study, which was lower than the previously reported carrier frequency in healthy population. Contrary to expectations, the number of P or LP variants did not increase with larger chromosome size or decrease with smaller chromosome size. Totally 83 novel P or LP variants were identified which could further expand the carrier variants spectrum of the Chinese population. GJB2: NM_004004.6:c.299_300delAT:p.His100fs*14 and C6:NM_000065.4:c.654T>A:p.Cys218* were found in two or more patients, which might be two underestimated carrier variants in Chinese population. We also found 9 late-onset or atypical symptoms autosomal/X-linked dominant Mendelian disorders causative genes, which were easily overlooked during pathogenicity analysis. These results can provide a strong basis for preventing and avoiding the prevalence rates of birth defects and reducing social and family burdens. By comparing with three different expanded carrier screening gene panels, we further confirmed carrier screening based on WES could offer more comprehensive assessment and WES was applicable for carrier screening.

Evaluation of prothrombotic risk of two PROC hotspot mutations (Arg189Trp and Lys193del) in Chinese population: a retrospective study

BACKGROUND

R189W and K193del of protein C (PC) were hotspot mutations in Chinese population with venous thromboembolism (VTE), but almost two-thirds of patients with above mutations coexisting with other genetically or aquiredly prothrombotic risk factors. The aim of this study is to clarify the independent contributions of R189W or K193del to VTE risk.

METHODS

490 unrelated patients with a personal history of VTE and 410 healthy participants were enrolled in this study. Data of their demographics, family history, genetic and acquired thrombosis risk factors were collected and statistically analyzed.

RESULTS

PC R189W and K193del were identified in 3/410 (0.7%) and 7/410 (1.7%) healthy controls, and in 27/490 (5.5%) and 43/490 (8.8%) patients with VTE, respectively. Notably, about 70% of these mutant carriers combined with other genetic or acquired thrombophilic factors. After adjustment for age, gender, other inherited and acquired risk factors, we demonstrated that R189W and K193del were associated with 5.781-fold and 4.365-fold increased risk of VTE, respectively, which were significantly lower than the prothrombotic risk of anticoagulant deficiencies induced from rare mutations. Independent R189W or K193del mutation was not associated with earlier first-onset age as well as higher recurrent rate of VTE. However, combination of other genetic or acquired thrombophilic factors had supra-additive effects on those consequences. The more additional risk factors the patients had, the younger first-onset ages and higher risk of recurrence would be.

CONCLUSIONS

As the most frequent mutations for PC deficiency in Chinese population, both R189W and K193del mutations had limited independent contributions to VTE development compared with other rare mutations in PROC gene, but may act in concert with other genetic defects or acquired thrombotic risk factors to produce the final severe phenotype.

A case of polycystic ovary syndrome with inevitable miscarriage and multi-site venous thrombosis caused by hereditary protein C deficiency

BACKGROUND

Polycystic ovarian syndrome (PCOS) affects up to 18% of reproductive-aged women and raises the risk of venous thromboembolic disease (VTE), due to metabolic features and an apparent fibrinolytic state. Recent studies have shown an increased risk of VTE (1.5- to 2-fold) in patients with PCOS as compared to those without PCOS. Mutations in the Protein C (PC) gene (PROC) lead to deficiency or dysfunction of the protein, Protein C deficiency is the main clotting physiological inhibitor of protein C cofactors, and is a risk factor for venous thrombosis, which can cause a variety of events, including miscarriage. This case report proposes a correlation between PCOS, protein C deficiency, venous thrombosis and inevitable miscarriage.

CASE PRESENTATION

A 33-year-old Chinese woman was diagnosed with Polycystic Ovary Syndrome (PCOS) in 2015. During the course of treatment, she took ethinylestradiol and cyproterone acetate tablets for more than one year. In 2016, she was sent to a hospital for emergency care due to explosive thrombosis (thrombosis in multiple parts of the body and pulmonary thrombosis). In 2020, the patient became pregnant via natural means and came to our hospital for treatment. During the second trimester, she experienced an inevitable miscarriage. High-throughput sequencing (NGS) of peripheral blood lymphocytes revealed that the patient had a protein C deficiency resulting from a heterozygous mutation deletion of 572_574 in exon 7.

CONCLUSION

PC deficiency in conjunction with PCOS and the concomitant use of oral contraceptive (COC) would increase the risk of VTE, especially in the early stages of COC use.

Genomic Analysis of Thrombophilia Variants in the General Population for the Creation of an Effective Preoperative Screening Tool

BACKGROUND

 The loss of a free flap in reconstructive microsurgery is a devastating complication in both the intraoperative and postoperative setting. Previous research has identified a variety of genetic polymorphisms that induce a hypercoagulable state and predispose patients to clot formation and subsequent free flap loss. We aim to review the risks of performing microsurgery on patients who are genetically predisposed to hypercoagulability, as well as identify options, for preoperative screening of inherited thrombophilia.

METHODS

 A thorough literature review was conducted with an online database. A total of 30 studies were reviewed to identify genetic polymorphisms that cause inherited thrombophilia. Through manual review of the literature, a table was created that included thrombotic risk factors and their associated genetic polymorphisms. If the information was available, prevalence for each thrombotic risk was also reported.

RESULTS

 Overall, 18 thrombotic risk factors that contribute to hereditary thrombophilia were identified and linked with specific genes and/or genetic polymorphisms. In studies that did not look at particular ethnic groups, 13 unique thrombotic risk factors were identified. In studies that examined specific ethnic groups exclusively, 12 thrombotic risk factors were identified and related to their respective gene or group of genes. Five of the 18 thrombotic risk factors identified were associated with increased risks of both venous and arterial thrombosis. The remainder of the thrombotic risk factors was associated with increased risk of venous thrombosis exclusively.

CONCLUSION

 The use of genetic screening tests for hereditary thrombophilia in the preoperative setting can serve as an effective preventative measure against postoperative thrombosis. Further exploration of thrombotic risk factors and their related genetic polymorphisms are important steps in reducing postoperative free flap loss.

Pediatric Retinal Detachment in Homozygous Protein C Deficiency: Genetic and Phenotypic Description of a Single Family

Homozygous protein C deficiency is a rare hypercoagulability disorder. This study describes the ocular manifestations and the genetic background in a family with two affected children. This is a retrospective review of ophthalmic examinations, investigations, genetic testing, and blood work-up of two children with homozygous protein C deficiency from a single family. A family with a positive history of consanguineous marriage was found to have two affected children with homozygous protein C deficiency. Abnormal visual behavior was the presenting symptom. Both children had bilateral total tractional retinal detachments at presentation. Skin manifestations included episodes of discoloration and bruising. Laboratory work-up revealed absent protein C activity. Genetic testing confirmed the presence of a homozygous pathogenic mutation in protein C gene (NM_000312.3: c.1297G>A: p.Gly433Ser). Homozygous protein C deficiency should be considered in the differential diagnosis of early-onset tractional retinal detachment in infancy. Although rare, the ophthalmologist may be the first to encounter the condition, and treatment with protein C replacement or anticoagulants may be life-saving. Examination under anesthesia with fluorescein angiography and laser treatment early in life may be warranted to preserve vision. [Ophthalmic Surg Lasers Imaging Retina. 2022;53:293-296.].

Clinical and genetic features of Chinese pediatric patients with severe congenital protein C deficiency who first presented with purpura fulminans: A case series study and literature review

INTRODUCTION

Purpura fulminans (PF) is a hematological emergency that can be caused by severe congenital protein C (PC) deficiency. It has been rarely reported in the Chinese population. We aimed to characterize the clinical and genetic features of Chinese pediatric patients with severe congenital PC deficiency who first presented with PF.

MATERIALS AND METHODS

Twelve pediatric patients were diagnosed with severe congenital PC deficiency with PF, which was diagnosed based on our hospital records and previous reports from 1988 to July 2021 in China. We evaluated the clinical and genetic features of these patients.

RESULTS

Nine patients (9/12, 75%) had onsets that were observed within the first 48 h after birth. Six patients had a family history of thromboembolism. There was no consanguinity. Other symptoms were intracranial thrombosis or hemorrhage (4, 33.3%), ocular lesions (2, 16.7%), gastrointestinal hemorrhage (2, 16.7%) and kidney infarction before birth (1, 8.3%). All but one of the patients (one case not detected) had a plasma PC activity of <10%. The genetic study indicated that in the eight patients with inherited PC deficiency, two were homozygous, five were compound heterozygous and one was heterozygous for PC deficiency.

CONCLUSION

This is the first and largest case series of Chinese pediatric patients with severe congenital PC deficiency who first presented with PF. It has been shown that treatment with both fresh frozen plasma and anticoagulants is recommended when PC concentrate is not easily available, especially in developing countries.

Supplementary research on K150del variant of activated protein C

Activated protein C (APC) is an anticoagulant with potent cytoprotective and anti-inflammatory effects. K150del, a natural variant of APC, is associated with reduced anticoagulant activity. We performed a comprehensive study to analyze the functional alterations of the K150del mutant. Transcriptome analysis of HEK 293T cells treated with wild and mutant APC revealed differentially expressed genes enriched in inflammatory, apoptotic, and virus defense-related signaling pathways. Both wild and mutant APC displayed concentration-dependent cytoprotective effects. Low concentrations of K150del mutant resulted in decreased anti-inflammatory and anti-apoptotic activities, whereas its higher concentrations restored these effects. Expression of virus defense-related genes improved in mouse lung tissues after repeated administration of the APC variant. These results suggest that the APC K150del mutant could help clinicians to accurately predict disease risks and serve as a potential auxiliary therapeutic in viral infections, including 2019 coronavirus disease (COVID-19).

Multiple arterial and venous thromboembolism in a male patient with hereditary protein C deficiency: A case report

RATIONALE

Hereditary protein C deficiency has a high prevalence in Asian populations, being the important risk factor associated with thrombophilia. Traditionally, conservative medication is the first choice for patients with hereditary protein C deficiency. However, there are few reports on whether aggressive surgical treatment can be performed when patients continue to develop life-threatening ischemic symptoms after adequate anticoagulant and thrombolytic therapy.

PATIENT CONCERNS

A 40-year-old male presented with right lower extremity pain for 1 week.

DIAGNOSIS

Computed tomography angiography (CTA) of lower extremity indicated arterial embolization of the right superficial femoral artery. Vascular ultrasonography showed old extensive thrombus in the deep vein of the left lower extremity. Electrocardiogram reported old anterior myocardial infarction. Sequencing of the gene encoding protein C (PROC) gene revealed that a heterozygous in-frame deletion mutation (c.577-579delAAG, p.192delK). Based on these findings, the diagnosis of hereditary protein C deficiency was made.

INTERVENTIONS

The patient was given low-molecular-weight heparin (LMWH) anticoagulation and urokinase treatment immediately. Then we performed the Fogarty catheter embolectomy with about 18.5 cm thrombus being removed and utilized the balloon catheter to dilate the anterior tibial artery. Despite given adequate anticoagulant and thrombolytic therapy postoperatively, the patient still had new thrombosis, and eventually underwent arterial embolectomy and amputation.

OUTCOMES

The patient was discharged with good wound healing and continued rivaroxaban treatment at a dose of 20 mg daily. The patient was followed-up monthly until 1 year: there was no adverse ischemic events occurred.

LESSONS

Aggressive surgical treatment may be the effective attempt for life-saving when conservative treatment as the first choice had unsatisfactory results in hereditary protein C deficiency patients. The novel oral anticoagulants (NOACs) could be more suitable than warfarin for the treatment and prevention of recurrence in patients with hereditary protein C deficiency.

Carvalho M, Morishita E. Racial differences in protein S Tokushima and two protein C variants as genetic risk factors for venous thromboembolism

BACKGROUND

Racial differences in genetic risk factors for venous thromboembolism (VTE) are elucidated, with factor V Leiden and prothrombin G20210A being prevalent among the Caucasian population but rare among non-Caucasians.

OBJECTIVES

To assess the worldwide distribution of three gene polymorphisms previously identified as genetic risk factors among East Asian subpopulations: protein S (PS) Tokushima (p.Lys196Glu), protein C (PC) p.Arg189Trp, and PC p.Lys193del.

METHODS

An international collaborative study group of seven centers in five countries-Japan, South Korea, Singapore, Hungary, and Brazil-was created, and genotype analyses were performed. A total of 2850 unrelated individuals (1061 patients with VTE and 1789 controls) were included.

RESULTS

PS Tokushima was confined to Japanese patients with VTE (allele frequency, 2.35%) and controls (1.12%), with an odds ratio (OR) of 2.15 (95% confidence interval, 1.16-3.99). PC p.Arg189Trp carriers were prevalent among Chinese and Malay patients with VTE in Singapore, with allele frequencies of 10.53% and 22.73%, respectively. Carriers of PC p.Lys193del were identified among Japanese and Korean patients with VTE (0.87% and 2.35%, respectively) and controls (0.36% and 1.07%, respectively), with the OR for VTE not being significant, and Chinese patients with VTE in Singapore (5.26%). In contrast, no carriers of PS Tokushima and two PC gene variants were found among patients with VTE or controls from Hungary, Brazil, or Indians in Singapore.

CONCLUSION

The three variants were prevalent among East and Southeast Asians, having some differences in geographic distribution, but were absent among Caucasian subpopulations and Brazilians.

Recurrent PROC and novel PROS1 mutations in Vietnamese patients diagnosed with idiopathic deep venous thrombosis

INTRODUCTION

Genetic mutations of PROC and PROS1 are well-known risk factors for deep venous thrombosis (DVT) in the Asian population. However, the genetic profile of Vietnamese patients with DVT remains elusive. This study aimed to investigate the spectrum of genetic mutations of these two genes in Vietnamese patients diagnosed with idiopathic DVT.

MATERIALS AND METHODS

A total of 50 Vietnamese patients diagnosed with idiopathic DVT were recruited in this study. The entire coding regions of the protein C and protein S genes were amplified and directly sequenced to determine genetic alterations.

RESULTS

Four and six genetic mutations were detected in protein C and protein S genes, respectively, in 24 Vietnamese DVT patients. PROC c.565C > T (p.R189W) was the most common mutation found in 13 out of 50 patients, while the mutations of PROS1 comprised three missense and three nonsense variants which diffuse along the gene.

CONCLUSIONS

This study shows that mutations of protein C and protein S genes are prevalent in Vietnamese patients diagnosed with idiopathic DVT, and PROC c.565C > T (p.R189W) was the most common genetic alteration.

C-terminal residues of activated protein C light chain contribute to its anticoagulant and cytoprotective activities

BACKGROUND

Activated protein C (APC) is an important homeostatic blood coagulation protease that conveys anticoagulant and cytoprotective activities. Proteolytic inactivation of factors Va and VIIIa facilitated by cofactor protein S is responsible for APC's anticoagulant effects, whereas cytoprotective effects of APC involve primarily the endothelial protein C receptor (EPCR), protease activated receptor (PAR)1 and PAR3.

OBJECTIVE

To date, several binding exosites in the protease domain of APC have been identified that contribute to APC's interaction with its substrates but potential contributions of the C-terminus of the light chain have not been studied in detail.

METHODS

Site-directed Ala-scanning mutagenesis of six positively charged residues within G142-L155 was used to characterize their contributions to APC's anticoagulant and cytoprotective activities.

RESULTS AND CONCLUSIONS

K151 was involved in protein S dependent-anticoagulant activity of APC with some contribution of K150. 3D structural analysis supported that these two residues were exposed in an extended protein S binding site on one face of APC. Both K150 and K151 were important for PAR1 and PAR3 cleavage by APC, suggesting that this region may also mediate interactions with PARs. Accordingly, APC's cytoprotective activity as determined by endothelial barrier protection was impaired by Ala substitutions of these residues. Thus, both K150 and K151 are involved in APC's anticoagulant and cytoprotective activities. The differential contribution of K150 relative to K151 for protein S-dependent anticoagulant activity and PAR cleavage highlights that binding exosites for protein S binding and for PAR cleavage in the C-terminal region of APC's light chain overlap.

Plasma phenotypes of protein S Lys196Glu and protein C Lys193del variants prevalent among young Japanese women

Protein S Tokushima (p.Lys196Glu) and two protein C gene variants (p.Arg189Trp, p.Lys193del) are hereditary thrombophilia in Japanese and Chinese populations, respectively; however, their diagnosis by plasma analyses is difficult because of the type II deficiency phenotype. Three gene variant genotypes were examined in young Japanese women (n = 231). Plasma total protein S activity and total protein S antigen levels were measured using a total protein S assay system, protein C and protein S activities by clot-based methods, and protein C and free protein S antigen levels by latex agglutination methods. protein S Tokushima (p.Lys196Glu) and protein C p.Lys193del variants were prevalent among participants with allele frequencies of 1.08 and 0.86%, respectively, whereas any carrier of protein C p.Arg189Trp variant was not identified. The plasma phenotype of the type II deficiency of protein S Tokushima heterozygotes was demonstrated by decreased total protein S activity with a normal total protein S antigen level; however, the protein C activities of protein C p.Lys193del heterozygotes were within reference intervals, whereas their protein C antigen levels were elevated. We compared the diagnostic accuracy of the total protein S activity/total protein S antigen ratio for identifying protein S Tokushima heterozygotes with that of the clot-based protein S activity/free protein S antigen ratio and found that sensitivity and specificity of 100% each was only achieved by the former. Protein S Tokushima and protein C p.Lys193del are prevalent among young Japanese women, and a plasma analysis using the total protein S assay system is more accurate than the clot-based protein S activity/free protein S antigen ratio for diagnosing protein S Tokushima carriers.

Genotypic and phenotypic character of Chinese neonates with congenital protein C deficiency: a case report and literature review

Background

Our objective was to study the phenotype of and molecular genetic mechanisms underlying congenital protein C (PC) deficiency in Chinese neonates. We report the case of a neonate who presented 4 h after birth with purpura fulminans of the skin and thrombosis in the kidney. We also carried out a through literature review to study the genotype and phenotype, relevance, diagnosis, management, and prognosis of neonates with congenital PC deficiency in China.

Case presentation and literature review

Following a septic work-up and check of PC and protein S (PS) levels that showed PC deficiency, we investigated the patient’s and her parents’ genotypes. Our patient was found to have a plasma PC level of 0.8%. Molecular testing revealed a compound heterozygous mutation of the PROC gene: From the father, a c._262 G > T p. ASP88Tyr mutation in exon 4; from the mother, a C. 400 + 5G mutation in intron 5 that had been previously reported as likely pathogenic. Both parents were found to have heterozygous mutations for PC deficiency. In China, 5 other cases of congenital PC deficiency in the neonatal period were reported in the literature. In those cases, purpura fulminans and thrombosis were the main symptoms, and homozygous or compound heterozygous mutations of the PROC gene were identified.

Conclusion

Congenital PC deficiency should be ruled out for neonates presenting with purpura fulminans and thrombosis.

Pathogenic variants of PROC gene caused type I activity deficiency in a familial Chinese venous thrombosis

Pathogenic mutation of protein C (PROC) gene results into the deficiency of PROC activity. This study aimed to identify the pathogenic genetic variants and to explore the functional consequence in Chinese familial venous thrombosis (VTE). Whole exome sequencing was performed to identify the pathogenic variants of anticoagulant factors. Serum coagulation and anti-coagulation factors activity were assayed to evaluate the genetic association. Functional study of PROC antigen secretion deficiency was conducted in VTE subjects and in vitro cell lines. One rare pathogenic variant (p.Ala178Pro) was identified in the four VTE subjects but not in the normal subjects from the family. An inframeshift variant (rs199469469) was also identified in a paediatric subject of the pedigree. Further evaluation of serum PROC activity levels in p.Ala178Pro variants VTE carriers showed significantly lower PROC activity compared to non-carriers. Furthermore, in vitro study showed that the p.Ala178Pro mutant cells had a consistent reduction in concentration of PROC antigen. In conclusions, our study demonstrated the pathogenic variant (p.Ala178Pro) contributed to PROC type I activity deficiency, which may be due to decreased secretion of PROC.

Diagnostic challenge of the newborn patients with heritable protein C deficiency

ABSTARCT

OBJECTIVE: The diagnosis of neonatal-onset protein C (PC) deficiency is challenging. This study aimed to establish the neonatal screening of heritable PC deficiency in Japan.

STUDY DESIGN

We determined the changes in plasma activity levels of PC and protein S (PS) in healthy neonates, and studied newborn patients with PROC mutation in the Japanese registry.

RESULT

Physiological PC and PS levels increased with wide range. The PC/PS-activity ratios converged after birth. The PC/PS-activity ratios of 19 patients with biallelic mutations, but not, 9 with monoallelic mutation, were lower than those of 13 without mutation. The logistic regression analyses established a formula including two significant variables of PC activity (cut-off < 10%, odds ratio = 30.0) and PC/PS-activity ratio (cut-off < 0.35, odds ratio = 22.7), with 93% sensitivity and 44% specificity for determining patients with mutation(s).

CONCLUSION

The PC/PS-activity ratio is an effective parameter for the genetic screening of neonatal-onset PC-deficiency in Japanese population.

Thrombophilia Caused by Beta2-Glycoprotein I Deficiency: In Vitro Study of a Rare Mutation in APOH Gene

This study aimed to explore the mechanism of a novel mutation (p.Lys38Glu) in apolipoprotein H (APOH) gene causing hereditary beta2-glycoprotein I (β2GPI) deficiency and thrombosis in a proband with thrombophilia. The plasma level of β2GPI was measured by ELISA and Western blotting, and anti-β2GPI antibody by ELISA. Lupus anticoagulant (LA) was assayed using the dilute Russell viper venom time. Deficiency of the major natural anticoagulants including protein C (PC), protein S (PS), antithrombin (AT) and thrombomodulin (TM) was excluded from the proband. A mutation analysis was performed by amplification and sequencing of the APOH gene. Wild type and mutant (c.112A>G) APOH expression plasmids were constructed and transfected into HEK293T cells. The results showed that the thrombin generation capacity of the proband was higher than that of the other family members. Missense mutation p.Lys38Glu in APOH gene and LA coexisted in the proband. The mutation led to β2GPI deficiency and thrombosis by impairing the protein production and inhibiting the platelet aggregation. It was concluded that the recurrent thrombosis of the proband is associated with the coexistence of p.Lys38Glu mutation in APOH gene and LA in plasma.

The prevalence and clinical manifestation of hereditary thrombophilia in Korean patients with unprovoked venous thromboembolisms

Background

Hereditary thrombophilia (HT) is a genetic predisposition to thrombosis. Asian mutation spectrum of HT is different from Western ones. We investigated the incidence and clinical characteristics of HT in Korean patients with unprovoked venous thromboembolism (VTE).

Methods

Among 369 consecutive patients with thromboembolic event who underwent thrombophilia tests, we enrolled 222 patients diagnosed with unprovoked VTE. The presence of HT was confirmed by DNA sequencing of the genes that cause deficits in natural anticoagulants (NAs). Median follow-up duration was 40±38 months.

Results

Among the 222 patients with unprovoked VTE, 66 (29.7%) demonstrated decreased NA level, and 33 (14.9%) were finally confirmed to have HT in a genetic molecular test. Antithrombin III deficiency (6.3%) was most frequently detected, followed by protein C deficiency (5.4%), protein S deficiency (1.8%), and dysplasminogenemia (1.4%). The HT group was significantly younger (37 [32–50] vs. 52 [43–65] years; P < 0.001) and had a higher proportion of male (69.7% vs. 47%; P = 0.013), more previous VTE events (57.6% vs. 31.7%; P = 0.004), and a greater family history of VTE (43.8% vs. 1.9%; P < 0.001) than the non-HT group. Age <45 years and a family history of VTE were independent predictors for unprovoked VTE with HT (odds ratio, 9.435 [2.45–36.35]; P = 0.001 and 92.667 [14.95–574.29]; P < 0.001).

Conclusions

About 15% of patients with unprovoked VTE had HT. A positive family history of VTE and age <45 years were independent predictors for unprovoked VTE caused by HT.

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.

The clinical presentation and genotype of protein C deficiency with double mutations of the protein C gene

BACKGROUND

Severe protein C (PC) deficiency is a rare heritable thrombophilia leading to thromboembolic events during the neonatal period. It remains unclear how individuals with complete PC gene (PROC) defects develop or escape neonatal stroke or purpura fulminans (PF).

PROCEDURE

We studied the onset of disease and the genotype of 22 PC-deficient patients with double mutations in PROC based on our cohort (n = 12) and the previous reports (n = 10) in Japan.

RESULTS

Twenty-two patients in 20 unrelated families had 4 homozygous and 18 compound heterozygous mutations. Sixteen newborns presented with PF (n = 11, 69%), intracranial thromboembolism and hemorrhage (n = 13, 81%), or both (n = 8, 50%), with most showing a plasma PC activity of <10%. Six others first developed overt thromboembolism when they were over 15 years of age, showing a median PC activity of 31% (range: 19-52%). Fifteen of the 22 patients (68%) had the five major mutations (G423VfsX82, V339M, R211W, M406I, and F181V) or two others (E68K and K193del) that have been reported in Japan. Three of the six late-onset cases, but none of the 16 neonatal cases, had the K193del mutation, which has been reported to be the most common variant of Chinese thrombophilia. A novel mutation of A309V was determined in a family of two patients with late onset.

CONCLUSIONS

The genotype of double-PROC mutants might show less diversity than heterozygous mutants in terms of the timing of the onset of thrombophilia (newborn onset or late onset).

Coagulation factor and protease pathways in thrombosis and cardiovascular disease

The biochemical characterisation of the proteolytic pathways that constitute blood coagulation was one of the most relevant achievements in biomedical research during the second half of the 20th century. Understanding these pathways was of crucial importance for improving global health through application in haemostasis and thrombosis pathologies. Immediately after the cloning of the genes corresponding to these proteins, mutations were discovered in them that were associated with imbalances in haemostasis. Later, the importance of coagulation pathways in other pathological processes was demonstrated, such as in atherosclerosis and inflammation, both essential processes involved in vascular disease. In the present review we evaluate the concepts that have allowed us to reach the integrated vision on coagulation that we have today. The thrombo-inflammation model encompassing these aspects includes a pivotal role for the proteases of the coagulation pathway as well as the regulatory proteins thereof. These concepts illustrate the importance of the coagulation cascade in cardiovascular pathology, not only in thrombotic processes, but also in atherosclerotic processes and in the response to ischaemia-reperfusion injury, making it a central mechanism in cardiovascular disease.

Thrombophilia in East Asian countries: are there any genetic differences in these countries?

In recent years, genetic analyses of congenital deficiencies of three anticoagulant proteins, antithrombin, protein C (PC) and protein S (PS), in East Asian patients with venous thromboembolism (VTE) have greatly increased. The PS-K196E mutation is often identified in the Japanese population with an allelic frequency of 0.86 %, and a total of approximately 10,000 Japanese are estimated to be homozygotes. The heterozygotes show PS anticoagulant activities ranging from 40 to 110 %, and 16 % lower mean anticoagulant activity than that in wild-type individuals. Specific assay methods to identify carriers of this mutation have recently been developed. The mutation carriers are at risk of thrombosis during pregnancy but do not appear to be at risk for adverse pregnancy outcomes. To promote future research into this mutation and its relation to thrombosis, a thrombosis-prone mouse strain with the PS K196E mutation has been developed. We found the PS-K196E mutation and the heterozygous PS-deficiency in mice caused increased VTE, but did not cause aggravation of ischemic stroke, unlike factor V Leiden mutation. Importantly, the PS-K196E mutation is only identified in Japanese. This suggests that although East Asian populations including Japanese, Chinese, and Koreans are geographically and genetically close, the PS-K196E mutation seems to be Japanese-specific, suggesting that the mutation is a recent occurrence and fixed within the Japanese population. Some recurrent genetic mutations predisposing to VTE have been reported in Chinese and Korean populations. Although the genetic background for VTE is known to differ between populations with Caucasian descent and East Asian populations, some of the recurrent mutations differ even within the East Asian populations.

[The preliminary research in paroxysmal nocturnal hemoglobinuria with thrombosis]

OBJECTIVE

To explore the high risk factors of thrombosis in paroxysmal nocturnal hemoglobinuria (PNH). It has been reported that in Chinese patients with venous thrombosis, the mutation frequency in PROC c.574_576 del (rs199469469), PROC c.565C>T (rs146922325) and THBD c.-151G>T (rs1698852) was higher than that of normal controls, indicating its importance in thrombophilia pathogenesis.

METHODS

142 patients with PNH diagnosed between 2009 and 2015 were enrolled in the study. Clinical data were analyzed and thrombophilia risk factors, such as the level of protein C, protein S, antithrombin III, APC resistance, blood fat, phospholipid antibody, were evaluated. Samples from patients and 100 normal controls were detected for the mutations of PROC c.574_576 del (rs199469469), PROC c.565C>T (rs146922325) and THBD c.-151G>T (rs1698852) by Sanger sequence.

RESULTS

Of the 142 PNH patients, 21 (14.8%) patients had at least 1 episode of thrombotic event. Only 2 patients had arterial thrombosis and 19 patients had venous thrombosis. The median age of patients with thrombosis was 35 years old, similar to those without episode (40 years old, P=0.687). The ratios of males and females were 1.33 in thrombosis group and 1.57 in non-thrombosis group (P=0.728) , respectively. Patients with thrombosis had the same disease pattern compared with those without episode. Although there was no difference in the level of hemoglobin, WBC and PLT count, and LDH level between patients with thrombosis and those without episode, patients with thrombosis showed higher RBC, higher percentage of CD59(-) granulocytes and RBC, and Flaer(-) granulocytes compared with those without episode. The routine thrombophilia screening tests did not show any difference either between PNH patients and normal controls, or between patients with or without thrombosis. There were two mutations in rs199469469 and rs16984852 sites in patients with PNH, but the mutated patients did not have any thrombosis. Mutation rs146922325 was found in PNH patients. The mutation rate was similar between PNH patients and normal controls, thrombotic PNH and non-thrombotic PNH (P>0.05).

CONCLUSIONS

Compared with non-thrombotic patients, PNH thrombotic patients have bigger PNH clone and higher RBC count. There are no differences among the routine thrombophilia factors and the three known venous eligible genes either between PNH patients and normal controls or between thrombotic and non-thrombotic PNH patients.

Air pollution and venous thrombosis: a meta-analysis

Exposure to air pollution has been linked to cardiovascular and respiratory disorders. However, the effect of air pollution on venous thrombotic disorders is uncertain. We performed a meta-analysis to assess the association between air pollution and venous thrombosis. PubMed, Embase, EBM Reviews, Healthstar, Global Health, Nursing Database, and Web of Science were searched for citations on air pollutants (carbon monoxide, sulfur dioxide, nitrogen dioxide, ozone, and particulate matters) and venous thrombosis. Using a random-effects model, overall risk estimates were derived for each increment of 10 μg/m³ of pollutant concentration. Of the 485 in-depth reviewed studies, 8 citations, involving approximately 700,000 events, fulfilled the inclusion criteria. All the main air pollutants analyzed were not associated with an increased risk of venous thrombosis (OR = 1.005, 95% CI = 0.998–1.012 for PM_2.5; OR = 0.995, 95% CI = 0.984–1.007 for PM₁₀; OR = 1.006, 95% CI = 0.994–1.019 for NO₂). Based on exposure period and thrombosis location, additional subgroup analyses provided results comparable with those of the overall analyses. There was no evidence of publication bias. Therefore, this meta analysis does not suggest the possible role of air pollution as risk factor for venous thrombosis in general population.

Genetic association of PROC variants with pulmonary embolism in Northern Chinese Han population

To evaluate SNPs (single nucleotide polymorphism) in PROC (protein C gene) associated with pulmonary embolism (PE) susceptibility in North Chinese Han population. A case-control study design was used, and patients with PE and healthy participants were enrolled from the Emerging Department of the several hospitals in Weifang, Shandong, China. SNPs in PROC were genotyped using Mass ARRAY system. The allele frequency of rs199469469 was significantly different between PE patients and the control [OR (95 % CI) = 5.00 (1.66-15.12), P = 0.004], and the difference remained significantly after controlling for age and gender [OR (95 % CI) = 5.34 (1.47-19.39), P = 0.011). The G(del)G in the haplotype includes rs1799809|rs199469469|rs2069928 was of a significantly difference (P = 0.016) among PE patients and the controls, and remained significant (P = 0.015) after adjustment for age and sex. Our study reports that PROC SNPs (rs199469469) might be associated with PE susceptibility, with the G allele of rs199469469 serving as the protective factors for incidence of PE. These findings may contribute to the understanding and primary prevention of PE.

Fetal hydrocephalus and neonatal stroke as the first presentation of protein C deficiency

Severe protein C-deficiency is a rare heritable thrombophilia of the newborn. Infants with biallelic PROC mutations present purpura fulminans and intracranial thromboembolism, while the prenatal onset of mutated heterozygotes remains unclear. We herewith present the first case of fetal ventriculomegaly and neonatal stroke associated with heterozygous PROC mutation. The infant was born to a healthy mother at 38 gestational weeks. The fetal growth had been normal, but the routine ultrasound screening had indicated mild hydrocephalus at 28 weeks of gestation. He developed convulsions two days after birth. Computed tomography of the brain revealed multiple hemorrhagic infarctions and ventriculomegaly. Dissociated levels of the plasma activity between protein C (21%) and protein S (42%) reached to determine the heterozygote of PROC c.574_576delAAG, a common thrombophilic predisposition in Asian ancestries. PC-mutant heterozygotes may have a limited high risk of cerebral thromboembolism during the perinatal course.

Hereditary protein S deficiency leads to ischemic stroke

Hereditary protein S (PS) deficiency is an independent risk factor for venous thromboembolism. However, the correlation between PS and arterial thrombotic disease, such as cerebral thrombosis, is not clear. The present study focused on the molecular mechanisms underlying ischemic stroke caused by a PS gene mutation in one family. The activity of antithrombin, protein C and PS in the plasma of the proband was measured, and the genes encoding PS were amplified and sequenced. The cellular localization and expression of PS were analyzed in HEK‑293 cells. The proband was a 50‑year‑old male. Plasma PS activity of the proband was 38.9%, which was significantly decreased compared with normal levels. Sequencing analysis revealed a PROS1 c.1486_1490delGATTA mutation on exon 12. This frameshift mutation converts Asp496 in the precursor PS into the termination codon. In addition, the PROS1 mutation was correlated with low PS activity in the family. Functional tests revealed that the mutant protein aggregated in the cytoplasm and its secretion and expression decreased. In conclusion, protein S mutation appeared to be the primary cause of thrombosis in the family of the present study. However, the correlation between PS deficiency and ischemic stroke requires further investigation.

Ethnic diversity in the genetics of venous thromboembolism

Genetic susceptibility is considered as a crucial factor for the development of venous thromboembolism (VTE). Epidemiologic and genetic studies have revealed clear disparities in the incidence of VTE and the distribution of genetic factors for VTE in populations stratified by ethnicity worldwide. While gain-of-function polymorphisms in the procoagulant genes are common inherited factors in European-origin populations, the most prevalent molecular basis for venous thrombosis in Asians is confirmed to be dysfunctional variants in the anticoagulant genes. With the breakthrough of genomic technologies, a set of novel common alleles and rare mutations associated with VTE have also been identified, in different ethnic groups. Several putative pathways contributing to the pathogenesis of thrombophilia in populations of African-ancestry are largely unknown, as current knowledge of hereditary and acquired risk factors do not fully explain the highest risk of VTE in Black groups. In-depth studies across diverse ethnic populations are needed to unravel the whole genetics of VTE, which will help developing individual risk prediction models and strategies to minimise VTE in all populations.

Progress in research into the genes associated with venous thromboembolism

BACKGROUND

Venous thromboembolism (VTE), including both deep vein thrombosis (DVT) and pulmonary embolism (PE), is a common, lethal disorder that affects hospitalized and non-hospitalized patients. This study aimed to review the progress in the research into VTE.

DATA SOURCES

We reviewed the studies about VTE and verified different genetic polymoriphisms of VTE.

RESULTS

The pathogenesis of VTE involves hereditary and acquired factors. Many studies indicated that the disorder of coagulation and fibirnolytic system is of utmost importance to this disease. Genetic polymoriphism-related VTE demonstrated significant differences among geographies and ethnicities.

CONCLUSION

VTE has many risk factors, but genetic factors play an important role.

Compound heterozygous protein C deficiency in a family with venous thrombosis: Identification and in vitro study of p.Asp297His and p.Val420Leu mutations

Hereditary protein C deficiency (PCD) is an autosomal inherited disorder associated with high risk for venous thromboembolism (VTE). This study aimed to explore the functional consequences of two missense mutations, p.Asp297His and p.Val420Ile, responsible for type I/II PCD and recurrent deep vein thrombosis (DVT) in a Chinese family. The plasma protein C activities (PC:A) of the proband and his sister were reduced to 4% and 5% of normal activity. However, protein C antigen (PC:Ag) concentrations were not equally decreased, with levels of 90.5% and 88.7%, respectively. Two missense mutations p.Asp297His and p.Val420Leu were identified in the protein C gene (PROC). The PC:A and PC:Ag levels in heterozygous state for p.Asp297His were 66% and 64.8%, whereas in heterozygous state for p.Val420Leu, these levels were 67% and 145%, respectively. Wild type (WT) and two mutant PROC cDNA expression plasmids were constructed and transfected into HEK 293T cells. Western blot analysis revealed that both p.Asp297His and p.Val420Leu showed a normal intracellular protein level. The extracellular protein level and specific activity of p.Asp297His were equally reduced to 37.7 ± 4.3% and 22.1 ± 2.5%, respectively. Mutant p.Val420Leu showed a relatively higher PC:Ag level and undetectable PC:A. Immunofluorescence staining revealed that WT and p.Val420Leu proteins were largely co-localized with both the protein disulfide isomerase (PDI) and cis-Golgi Marker (GM130), while the PC p.Asp297His mutant protein was mainly co-localized with PDI and much less co-localized with GM130. The thrombosis symptom in this family was associated with the two missense mutations in the PROC gene.

Dysfunction of protein C anticoagulant system, main genetic risk factor for venous thromboembolism in northeast Asians

Venous thromboembolism (VTE) is a life threatening medical disorder worldwide. A great deal of evidence suggests that prevalence of VTE varies significantly among ethnic populations, with consistently lower incidence found in Asians. While the distribution of genetic risk factors may vary among races, genetic risk factors can play a major role among individuals with different genetic backgrounds. Two clinically evaluated low-frequency genetic mutations that predispose to VTE--the factor V Leiden mutation and prothrombin G20210A mutation--are found predominantly in Caucasians, and virtually never in Asians. The findings of a recent genetic study of VTE in northeast Asians, which greatly advanced our knowledge in this area, indicate that the most frequent genetic risk factors for VTE in northeast Asians can be attributed to a dysfunction of the protein C anticoagulant system. Several low-frequency genetic mutations, PROS1 p.Lys196Glu in Japanese and PROC p.Arg189Trp and p.Lys193del in Chinese, are significantly associated with increased risk for VTE, with odds ratio more than 2 through the reduced protein C anticoagulant activity. Construction of a multifactorial model based on the genetic risk factors in the protein C anticoagulant system could facilitate genetic counseling for VTE risk in these populations. The influence of prevalent genetic mutations on the risk of VTE should be further investigated in Asian countries.

Identification of APOH polymorphisms as common genetic risk factors for venous thrombosis in the Chinese population

BACKGROUND

Venous thrombosis (VT) is a worldwide medical problem. In order to identify individuals at high risk early, it is necessary to find more genetic risk factors. Nowadays, the studies on genetic factors of thrombosis are mainly focused on coagulation and anticoagulation factors. The exploration of other proteins involved in thrombosis and hemostasis may lead to a breakthrough.

OBJECTIVES

We used APOH as a candidate gene to investigate the existence of genetic variation that could increase the risk of thrombosis.

METHODS/RESULTS

In the current study, with a resequencing method followed by a case-control study, four polymorphisms (c.-32C>A, c.422T>C, c.461G>A, and c.1004G>C) in APOH (encoding β2 -glycoprotein I) were found to be in high linkage disequilibrium, which could result in three haplotypes. The H2 heterozygotes and H3 homozygotes had approximately 1.5-fold and seven-fold increased risks for VT, respectively. The minor allele frequency in the general population was ~ 10%. In addition, H3 individuals showed a significantly decreased level of β2 -glycoprotein I, but an increased level of thrombin generation. Functional tests indicated that the mutant β2 -glycoprotein I had a significantly lower capacity to extend thrombin clotting time and increase thrombin generation potential.

CONCLUSIONS

This study revealed APOH as a new candidate gene associated with thrombosis, and further genetic research on this gene in patients in whom the cause of thrombophilia is unknown is therefore warranted.

Distinct frequencies and mutation spectrums of genetic thrombophilia in Korea in comparison with other Asian countries both in patients with thromboembolism and in the general population

Hereditary natural anticoagulant deficiencies are the major cause of genetic thrombophilia in Asia. Given the growing acknowledgment of the risk of venous thromboembolism in Asian populations, we investigated the frequency and mutation spectrums of natural anticoagulant deficiency in Korea. The group of patients consisted of consecutive patients with venous thromboembolism screened for thrombophilia. Genetic tests were performed on suspicion of natural anticoagulant deficiency. For the population group, >3,000 individuals were screened from routine check-ups, and those with a low level (<1(st) percentile) of natural anticoagulant underwent genetic tests. Mutations were detected by direct sequencing of PROC, PROS1, and SERPINC1, followed by additional multiplex ligation-dependent probe amplification for PROS1 and SERPINC1 for dosage mutations. Among 500 patients screened, 127 were suspected of having a natural anticoagulant deficiency, and this was genetically confirmed in 71: protein C deficiency in 36 (50.7%), antithrombin deficiency in 21 (29.6%), and protein S deficiency in 14 (19.7%). Among 3,129 individuals from the population who were screened, the frequency of natural anticoagulant deficiency was ~1.0%: antithrombin deficiency 0.49%, protein C deficiency 0.35%, and protein S deficiency 0.16%. Two PROC mutations causing type I protein C deficiency were prevalent (Arg211Trp and Met406Ile in patients and Arg211Trp in the population). Two SERPINC1 mutations causing type II antithrombin deficiency, Arg79Cys and Ser158Pro, were prevalent in the population group. This is the first study on the genetic epidemiology of natural anticoagulant deficiencies in Korea. The results demonstrated that the frequencies and spectrum of mutations underlying genetic thrombophilia in Korea are different not only from those in Caucasians but also those in other Asian populations.

Molecular basis of protein S deficiency in China

Protein S (ProS) is a physiological inhibitor of coagulation with an important function in the down-regulation of thrombin generation. ProS deficiency is a major risk factor for venous thrombosis. This study enrolled 40 ProS-deficient probands to investigate the molecular basis of hereditary ProS deficiency in Chinese patients. A mutation analysis was performed by resequencing the PROS1 gene. Large deletions were identified by multiplex ligation-dependent probe amplification (MLPA) analysis. A total of 20 different mutations, including 15 novel mutations, were identified in 21 of the 40 index probands. Small mutations were detected in 18 (45.0%) probands, and large deletions were found in 3 (7.5%) probands, leaving 19 (47.5%) patients without causative variants. To evaluate the functional consequences of 2 novel missense variants, ex vivo thrombin-generation assays, bioinformatics tools, and in vitro expression studies were employed. The p.Asn365Lys ProS variant was found to have moderately impaired secretion and reduced activated protein C cofactor activity. In contrast, the p.Pro410His mutant appeared to have severely impaired secretion but full anticoagulant activity. This study is the largest investigation of ProS deficiency in China and the first investigation of the influence of Type I ProS missense mutations on the global level of coagulation function. The p.K196E mutation, which is common in the neighboring Japanese population, was not found in our Chinese population, and null mutations were common in our Chinese population but not common in Japan. Further genetic analysis is warranted to understand the causes of ProS deficiency in patients without a genetic explanation.

Common genetic risk factors for venous thrombosis in the Chinese population

Venous thrombosis is a major medical disorder caused by both genetic and environmental factors. Little is known about the genetic background of venous thrombosis in the Chinese population. A total of 1,304 individuals diagnosed with a first venous thrombosis and 1,334 age- and sex-matched healthy participants were enrolled in this study. Resequencing of THBD (encoding thrombomodulin) in 60 individuals with venous thrombosis and 60 controls and a functional assay showed that a common variant, c.-151G>T (rs16984852), in the 5' UTR significantly reduced the gene expression and could cause a predisposition to venous thrombosis. Therefore, this variant was genotyped in a case-control study, and results indicated that heterozygotes had a 2.80-fold (95% confidence interval = 1.88-4.29) increased risk of venous thrombosis. The THBD c.-151G>T variant was further investigated in a family analysis involving 176 first-degree relatives from 38 index families. First-degree relatives with this variant had a 3.42-fold increased risk of venous thrombosis, and their probability of remaining thrombosis-free was significantly lower than that of relatives without the variant. In addition, five rare mutations that might be deleterious were also identified in thrombophilic individuals by sequencing. This study is the largest genetic investigation of venous thrombosis in the Chinese population. Further study on genetics of thrombosis should focus on resequencing of THBD and other hemostasis genes in different populations.