Analysis of four hereditary protein C deficiencies associated with vascular thromboembolism

OBJECTIVE

To analyze the clinical features and gene mutations in four families with hereditary protein C (PC) deficiency and explore their association with vascular thromboembolism.

METHODS

The clinical data of four patients with PC deficiency were retrospectively analyzed. Venous blood samples were collected from the four affected patients and their family members, and relevant coagulation indexes and thrombin production and inhibition tests were performed. PCR was used to amplify and directly sequence the PROC gene of the probands. Software analysis was conducted to assess the conservativeness and pathogenicity of the mutated loci. Protein models were constructed to analyze the spatial structure before and after the mutation.

RESULTS

Thrombin generation and inhibition assays demonstrated impaired anticoagulation in all four probands. Proband 1 and 4 presented clinically with pulmonary embolism and lower extremity deep vein thrombosis (DVT), Proband 2 with cerebral infarction, and Proband 3 with DVT. Genetic analysis revealed the presence of the following mutations: c.541T > G heterozygous missense mutation, c.577-579delAAG heterozygous deletion mutation, c.247-248insCT heterozygous insertion mutation, c.659G > A heterozygous missense mutation, and a new variant locus c.1146_1146delT heterozygous deletion mutation in the four probands, respectively. In particular, c.1146_1146delT heterozygous deletion mutations not reported previously. Conservativeness and pathogenicity analyses confirmed that most of these amino acid residues were conserved, and all the mutations were found to be pathogenic. Analysis of protein modeling revealed that these mutations induced structural alterations in the protein or led to the formation of truncated proteins. According to the American College of Medical Genetics and Genomics (ACMG) classification criteria and guidelines for genetic variants, c.1146_1146delT was rated as pathogenic (PVS1 + M2 + PM4 + PP1 + PP3 + PP4).

CONCLUSION

The identified mutations are likely associated with decreased PC levels in each of the four families. The clinical manifestations of hereditary PC deficiency exhibit considerable diversity.

Ser252Asn Mutation Introduces a New N-Linked Glycosylation Site and Causes Type IIb Protein C Deficiency

BACKGROUND

 Protein C (PC) is a vitamin K-dependent anticoagulant serine protease zymogen which upon activation by the thrombin-thrombomodulin (TM) complex downregulates the coagulation cascade by degrading cofactors Va and VIIIa by limited proteolysis. We identified a thrombosis patient who carried a heterozygous mutation c.881G > A, p.Ser252Asn (S252N) in PROC. This mutation was originally described in a report of novel mutations in patients presenting with defective PC anticoagulant activity in Paris. The research identified PC-S252N (the "Paris" mutation) in a propositus and her family members and highlighted the critical role of Ser252 in the anticoagulation process of activated PC (APC).

MATERIAL AND METHODS

 We expressed the PC-S252N mutant in mammalian cells and characterized the properties in coagulation assays to decipher the molecular basis of anticoagulant defect of this mutation.

RESULTS

 We demonstrated that PC-S252N had a diminished ability to TM binding, which resulted in its impaired activation by the thrombin-TM complex. However, APC-S252N exhibited a slightly stronger cleavage capacity for the chromogenic substrate. Meanwhile, the catalytic activity of APC-S252N toward FVa was significantly reduced. Sequence analysis revealed that Ser252 to Asn substitution introduced a new potential N-linked glycosylation site (252NTT254) in the catalytic domain of PC, which adversely affected both the activation process of PC and anticoagulant activity of APC.

CONCLUSION

 The new N-glycosylation site (252NTT254) resulting from the mutation of Ser252 to Asn252 in PROC affects the overall structure of the protease, thereby adversely affecting the anticoagulant function of protein C. This modification has a negative impact on both TM-promoted activation of protein C and APC cleavage of FVa, ultimately leading to thrombosis in the patient.

Validation for the function of protein C in mouse models

Objectives

Protein C (PC) is an anticoagulant that is encoded by the PROC gene. Validation for the function of PC was carried out in mouse models.

Methods

In this study, autosomal recessive PC deficiency (PCD) was selected as the target, and the specific mutation site was chromosome 2 2q13-q14, PROC c.1198G>A (p.Gly400Ser) which targets G399S (GGT to AGC) in mouse models. To investigate the role of hereditary PC in mice models, we used CRISPR/Cas9 gene editing technology to create a mouse model with a genetic PCD mutation.

Results

The two F0 generation positive mice produced using the CRISPR/Cas9 gene editing technique were chimeras, and the mice in F1 and F2 generations were heterozygous. There was no phenotype of spontaneous bleeding or thrombosis in the heterozygous mice, but some of them were blind. Blood routine results showed no significant difference between the heterozygous mice and wild-type mice (P > 0.05). Prothrombin time (PT), activated partial thromboplastin time (APTT), and thrombin time (TT) were prolonged in the heterozygous mice, while the level of fibrinogen content (FIB) decreased, suggesting secondary consumptive coagulation disease. The protein C activity of heterozygous mice was significantly lower than that of wild-type mice (P < 0.001), but there was no significant difference in protein C antigen levels (P > 0.05). H&E staining showed steatosis and hydrodegeneration in the liver of heterozygous mice. Necrosis and exfoliated epithelial cells could be observed in renal tubule lumen, forming cell or granular tubules. Hemosiderin deposition was found in the spleen along with splenic hemorrhage. Immunohistochemistry demonstrated significant fibrin deposition in the liver, spleen, and kidney of heterozygous mice.

Conclusion

In this study, heterozygotes of the mouse model with a PC mutation were obtained. The function of PC was then validated in a mouse model through genotype, phenotype, and PC function analysis.

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.

[Genetic predisposition to early-onset thrombophilia: a study on challenges in personalized medicine for mothers, infants, and children]

The number of reports on genetic predisposition to pediatric thrombosis is increasing. The risk of thrombosis in childhood varies according to patient age, and the contribution of genetic predisposition also differs. The term early-onset thrombophilia, which occurs until the age of 20 years in patients with genetic diagnosis, was defined. Then, the registry in Japan was established. Further, publications were reviewed comprehensively, and results revealed the genetic and clinical characteristics of patients. Less than 60% of patients presented with protein C (PC) deficiency, and over half of them had PC-gene monoallelic variants. The number of patients with protein S or antithrombin deficiency increased with age. None of them were aged between 6 and 8 years. PC-Tottori and protein S-Tokushima, which are high-frequency and low-risk variants in Japanese, contributed to the development of thrombosis. However, PC-Tottori did not affect the development of severe PC deficiency. One exceptional de novo PC-deficient variant was identified in 32 EOT families, and thrombosis developed concurrently in three pairs of mothers-newborns. Appropriate EOT screening tests targeting PC deficiency are required to prevent maternal and neonatal thromboses.

[Analysis of PROC gene variant in a Chinese pedigree affected with hereditary protein C deficiency]

OBJECTIVE

To explore the molecular pathogenesis of a Chinese pedigree affected with inherited protein C (PC) deficiency.

METHODS

The protein C activity (PC:A) and protein C antigen (PC:Ag) of the proband and his family members were determined by a chromogenic substrate method and enzyme-linked immunosorbent assay, respectively. The proband was subjected to whole exome sequencing. Candidate variants were verified by Sanger sequencing of other members of the pedigree.

RESULTS

The PC:A and PC:Ag of proband were reduced to 15% and 11%, respectively. The above parameters of his parents and elder sister were also decreased to approximately 50% of reference values. Next generation sequencing has revealed that the proband has harbored a heterozygous c.572_574delAGA (p.Glu191_Lys192delinsGlu) variant in exon 7 and a missense c.752C>T (p.Ala251Val) variant in exon 8 of the PROC gene. His father was heterozygous for the c.572_574delAGA variant, while his mother and elder sister were heterozygous for the c.752C>T variant. According to the American College of Medical Genetics and Genomics Standards and Guidelines, the c.572_574delAGA (p.Glu191_Lys192 delinsGlu) variant was predicted to be likely pathogenic (PS1+PM4+PP3). c.752 C>T (p.Ala251Val) variant was also likely pathogenic (PS1+PM1+PP3).

CONCLUSION

The deletional variant of c.572_574delAGA (p.Glu191_Lys192delinsGlu) in exon 7 and missense variant c.752C>T (p.Ala251Val) in exon 8 of the PROC gene probably underlay the inherited protein C (PC) deficiency in this pedigree. Above finding has enriched the spectrum of PROC gene variants and provided a basis for genetic counseling for this pedigree.

Compound heterozygous protein C deficiency with pulmonary embolism caused by a novel PROC gene mutation: Case report and literature review

RATIONALE

Protein C is an anticoagulation agent, and protein C deficiency results in vascular thrombosis disease. Hereditary protein C deficiency is a risk factor for pulmonary embolism in adults. Pathogenic variants of the Protein C, Inactivator Of Coagulation Factors Va And VIIIa (PROC) gene which encodes protein C have been identified as a cause of protein C deficiency.

PATIENT CONCERNS

We describe a patient with a novel mutation in the PROC gene who was diagnosed with pulmonary embolism in a Chinese family.

DIAGNOSIS

According to the results of the pulmonary computed tomography angiography (CTA) and the level of blood protein C, the patient was diagnosed with pulmonary embolism caused by protein C deficiency.

INTERVENTIONS

Whole-exome sequencing (WES) was performed for the molecular analysis.

OUTCOME

The results of patient's deoxyribonucleic acid revealed a heterozygous mutation (c.237 + 5G > A) in intron 3 of the PROC gene. His father also harbored the same mutation in the PROC gene. We also reviewed the protein C deficiencies caused by PROC gene mutations in cases.

LESSONS

A novel mutation in intron 3 of PROC gene has not been previously reported in patients with pulmonary embolism caused by protein C deficiency. After anticoagulation therapy, the patient recovered, and CT showed resolution of the thrombosis. Pulmonary embolism may be caused by protein C deficiency and the rare compound heterozygous mutation in intron 3 of the PROC gene could cause protein C deficiency via impairment of the secretory activity of protein C.

[Analysis of the molecular pathogenesis of hereditary protein C deficiency due to a p.Gly86Asp variant of the PROC gene]

OBJECTIVE

To explore the molecular pathogenesis of hereditary protein C (PC) deficiency due to a p.Gly86Asp variant of the PROC gene through in vitro expression experiment.

METHODS

Wild type and Gly86Asp mutant expression plasmids of PC were constructed and respectively transfected into HEK 293FT cells. Total RNA was extracted from the transfected cells, and the expression of PROC gene was determined by quantitative real-time PCR (qRT-PCR). PC antigen (PC:Ag) in the supernatant of cell culture and cell lysate was determined by enzyme-linked immunosorbent assay (ELISA), and the level of PC protein was detected by Western blotting.

RESULTS

qRT-PCR has detected no significant difference in the transcription level of wild-type and mutant-type PC. Compared with the wild type, the level of mutant PC:Ag in the supernatant and cell lysate were 81.3%±2.6% and 110.0%±2.8%, respectively. No difference was detected in the molecular weight between the wild-type and mutant-type PC by Western blotting. The PC content of mutant type was higher than wild-type in cell lysate, while the opposite was found with the cell culture supernatant.

CONCLUSION

The impaired secretion by mutant PC may be the molecular mechanism of PC deficiency caused by the p.Gly86Asp variant.

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.].

A Series of 14 Polish Patients with Thrombotic Events and PC Deficiency-Novel c.401-1G>A PROC Gene Splice Site Mutation in a Patient with Aneurysms

Objectives: Protein C (PC) deficiency is an inherited thrombophilia with a prevalence of 0.5% in the general population and 3% in subjects with a first-time deep vein thrombosis (DVT). Here we report a series of 14 PC-deficient Polish patients with comprehensive clinical and molecular characteristics, including long-term follow-up data and a deep mutational analysis of the PROC gene. Patients and Methods: Fourteen unrelated probands (mean ± SD age 43.8 ± 13.0 years) with suspicion of PC deficiency, who experienced thromboembolic events and a majority of whom received anticoagulants (92.8%), were screened for PROC mutations by sequencing the nine PROC exons and their flanking intron regions. Results: Ten probands (71.4%) had missense mutations, two patients (14.3%) carried nonsense variants, and the other two subjects (14.3%) had splice-site mutations, the latter including the c.401-1G>A variant, reported here for the very first time. The proband carrying the c.401-1A allele had a hepatic artery aneurysm with a highly positive family history of aneurysms and the absence of any mutations known to predispose to this vascular anomaly. Conclusion: A novel detrimental PROC mutation was identified in a family with aneurysms, which might suggest yet unclear links of thrombophilia to vascular anomalies, including aneurysms at atypical locations in women. The present case series also supports data indicating that novel oral anticoagulants (NOACs) are effective in PC deficient patients.

[Clinical phenotype and gene mutation analysis of 12 patients with hereditary protein C deficiency in different families]

Objective: To investigate the molecular pathogenesis and clinical features of unrelated 12 patients with inherited coagulation protein C (PC) deficiency in Chinese population. Methods: The PC activity (PC:A) and PC antigen (PC:Ag) were detected by chromogenic substrate and enzyme linked immunosorbent assay, respectively. The nine exons and flanking sequences of the protein C (PROC) gene were amplified by polymerase chain reaction with direct sequencing, and the suspected mutations were validated by reverse sequencing (clone sequencing for deletion mutations) . Results: The PC:A of the 12 probands decreased significantly, ranging from 18% to 55%, and the PC:Ag of the 10 probands decreased significantly. Eleven mutations were found, out of which four mutations [c.383G>A (p.Gly128Asp) , c.997G>A (p.Ala291Thr) , c.1318C>T (p.Arg398Cys) , and c.532G>C (p.Leu278Pro) ] were discovered for the first time. Six mutations were in the serine protease domain, four mutations were located in epidermal growth factor (EGF) -like domains, and one mutation was located in activation peptide. There were two deletion mutations (p.Met364Trp fsX15 and p.Lys192del) , and the rest were missense mutations. Mutations p.Phe181Val and p.Arg189Trp were identified in three unrelated families. All mutations may be inherited, and consanguineous marriages were reported in two families. Among the probands, nine cases had venous thrombosis, two cases had poor pregnancy manifestations, and one case had purpura. Conclusion: Patients with PC deficiency caused by PROC gene defects are prone to venous thrombosis, especially when there are other thrombotic factors present at the same time.

[Phenotype and genetic mutation analysis of an inherited protein C deficiency pedigree]

Objective: A phenotypic and gene mutation study was carried out to investigate the molecular mechanism of inherited protein C deficiency in a family with the disorder. Methods: The proband was a 21-year-old male who was admitted to hospital due to swelling of the left lower limb for 3 months and hemoptysis with chest tightness for more than 1 week. The clinical diagnosis was pulmonary embolism and deep vein thrombosis of the left lower limb. Plasma protein C activity, protein S activity and antithrombin Ⅲ activity were detected in the patient and their family members. Whole exon sequencing was used to analyze a total of 199 genes associated with thrombus susceptibility of the patient. After the mutation was found and Sanger sequencing was used to verify whether the family members carried the same gene mutations as the patient. The conservation of amino acid mutation sites was analyzed by using the software ClustalX-2.1-win. The damage of mutations to protein function was analyzed by PROVEAN and PolyPhen-2 online bioinformatics software. Finally, PyMOL 2.3 software was used to analyze the protein model. Results: The patient and four family members all had the identical heterozygous missense mutation c.1019 C>T (p. Thr340Met) in exon 9 of the protein C gene, resulting in various degrees of protein C deficiency. The Thr340 amino acid was discovered to be poorly conserved in seven homologous species after investigation with the clustalx-2.1-win software. P. Thr340Met was found to be a detrimental mutation by both PROVEAN and PolyPhen-2 online bioinformatics program. The mutation of Thr340 to Met340 caused the hydrogen bond between Thr340 and Gln226 to dissolve, changing the spatial arrangement of protein C, which might be the main explanation for the lower protein C activity, according to the protein model. Conclusions: Protein C deficiency in this family was caused by a hybrid missense mutation C. 1019 C>T (p. Thr340Met). Protein C deficiency may present in varying severity among mutation carriers at the same locus of the protein C gene. Whole-exome sequencing may be considered in young patients with spontaneous venous thromboembolism, even if there is no relevant family history.

Sagittal sinus thrombosis in a patient with familial Protein C deficiency: Highlighting the impact of thrombophilia testing

Plasma protein-C is a natural anticoagulant that inactivates factors Va and VIIIa. Familial protein C deficiency is inherited as an autosomal dominant disorder. The homozygous or compound heterozygous type may present early as purpura fulminant, while the heterozygous type can present as thromboembolism later in life. Presented in this report is a case of a 21-year-old female patient with protein-C deficiency, confirmed by thrombophilia investigations. She experienced recurrent deep vein thrombosis and cerebral sinus thrombosis due to thrombotic occlusion. She had a family history of deep vein thrombosis. Hence, high-risk cases should be seriously considered for long term anticoagulation therapy. The utility versus futility of thrombophilia testing in a particular situation is discussed to address and ensure safe practice among patients with thromboembolism.

[Phenotypic and genotypic analysis of a pedigree affected with hereditary protein C deficiency]

OBJECTIVE

To analyze the phenotype and genetic variant in a pedigree affected with inherited protein C (PC) deficiency.

METHODS

The proband and her family members (7 individuals from 3 generations) were tested for plasma protein C activity (PC:A), protein C antigen (PC:Ag) content and other coagulation indicators. All of the 9 exons and flanking sequences of the proband's PROC gene were amplified by PCR and sequenced. Suspected variants were verified by reverse sequencing of the proband and her family members. Bioinformatic software was used to analyze the pathogenicity and conservation of the variant site. Swiss-PdbViewer was used to analyze the three-dimensional model and the interaction with the mutant amino acid.

RESULTS

The PC:A and PC:Ag of the proband, her grandmother, father and elder brother were decreased to 55%, 52%, 48%, 51% and 53%, 55%, 50%, 56%, respectively. Genetic analysis showed that the four individuals have all carried heterozygous c.1318C>T (p.Arg398Cys) missense mutation in exon 9 of the PROC gene. The score of MutationTaster was 0.991, PROVEAN was -3.72, and FATHMM was -2.49, all predicted it to be a harmful mutation. Phylogenetic analysis also showed that Arg398 was weakly conservative among homologous species. Protein model analysis showed that, in the wild type, Arg398 can form a hydrogen bond with Glu341 and Lys395 respectively, when it was mutated to Cys398, the hydrogen bond with Glu341 disappears and an additional hydrogen bond was formed with Lys395, which has changed the spatial structure of the protein.

CONCLUSION

The heterozygous missense mutation c.1318C>T (p.Arg398Cys) of the PROC gene probably underlay the decreased PC:A and PC:Ag in this pedigree.

The risk of arterial thrombosis in carriers of natural coagulation inhibitors: a prospective family cohort study

BACKGROUND

Whether the carriership of inherited antithrombin (AT), protein C (PC), and protein S (PS) deficiency increases the risk of arterial thromboembolic events (ATE) is controversial. This information has the potential to inform the management of family members of probands with inherited deficiency of natural anticoagulants.

PATIENTS/METHODS

We conducted a large prospective family cohort study in 640 subjects (of whom 341 carriers and 299 non-carriers) belonging to 86 families with inherited deficiency of AT, PC, or PS.

RESULTS

A total of 4240 and 3810 patient-years were available for carriers and non-carriers, respectively. Risk factors for atherosclerosis were similarly distributed in the two groups. Of the 26 ATE that were recorded, 19 occurred in carriers (5.6%), as compared to 7 in non-carriers (2.3%) [p = 0.07]. After adjusting for confounders, the hazard ratio (HR) for ATE was 4.9 (95% CI 1.5-16.3) in carriers as compared to non-carriers.

CONCLUSIONS

Among family members of probands with an inherited deficiency of natural anticoagulants, carriers exhibit a risk of ATE that is almost five times higher than in non-carriers.

Pathogenic variants of PROC gene caused type II activity deficiency in a Chinese family: A case report

RATIONALE

Hereditary Protein C (PC) deficiency is a rare genetic disorder caused by PROC gene mutation. In this article, we report a case of PC deficiency in a Chinese family due to a novel PROC gene mutation.

STUDY SUBJECT

The proband presented with recurrent cerebral infarction over the course of the previous 3 years. He was admitted to the hospital due to signs of mental retardation.

DIAGNOSES

Physical examination, laboratory tests, and magnetic resonance imaging demonstrated that the proband had a manifestation of PC deficiency that included acute cerebral infarction. DNA sequencing analysis revealed a missense variant, c.1015G > A (p.V339 M from valine to methionine) in exon 9 of the PROC gene. In addition, Sanger sequencing confirmed that the proband's son was heterozygous for the same variant. Therefore, the PROC gene mutation was transmitted in an autosomal dominant inheritance manner.

INTERVENTIONS

The patient was treated with a daily dosage of Warfarin (3.5 mg) and was scheduled to undergo regular blood coagulation tests.

OUTCOMES

At the 3-month follow-up appointment, the patient showed improvements in his overall health condition.

LESSONS

We identified a novel missense mutation in the PROC gene in a Chinese family which caused a decrease in the PC antigen level and recurrent cerebral infarction.

Recurrent Cerebral Venous Thrombosis Treated with Direct Oral Anticoagulants in a Japanese Man with Hereditary Protein C Deficiency

We herein report a case involving a 32-year-old Japanese man with recurrent cerebral venous thrombosis due to hereditary protein C deficiency. He was admitted to our hospital with impaired consciousness. Brain magnetic resonance imaging demonstrated high intensities diffusely along the bilateral sulci and magnetic resonance venography revealed left transverse sinus and superior sagittal sinus stenoses. His father had a history of cerebral infarction and venous thrombosis. The protein C activity level examined by chromogenic synthetic substrate assay was markedly reduced. He was diagnosed with protein C deficiency, and a genetic analysis revealed a heterozygous mutation at exon 3 c.199G>A,p.Glu67Lys on the protein C gene. Four months later, at his second admission, he had transient aphasia, and his protein C activity was under 10%. We switched warfarin to the direct oral anticoagulants edoxaban. He remains fully recovered with no adverse events after the administration of edoxaban for a year. Direct oral anticoagulants may be a new tool for treating cerebral venous thrombosis due to hereditary protein C deficiency.

[Phenotypic and genotypic analysis of a pedigree affected with hereditary protein C deficiency due to heterozygous deletional mutation of PROC gene]

OBJECTIVE

To analyze the phenotype and genetic variants of a pedigree affected with hereditary protein C (PC) deficiency.

METHODS

The protein C activity (PC:A) of the proband and her family members (a four-generation pedigree including 11 individuals) were tested by chromogenic substrate method, and the protein C antigen (PC:Ag) was detected with an enzyme-linked immunosorbent assay(ELISA). The 9 exons and flanking sequences of the protein C (PROC) gene were amplified by PCR and directly sequenced. Suspected mutation was validated by clone sequencing and in other members of the family. MutationTaster and ClustalX-2.1-win was used to analyze the pathogenicity and conservation of the mutation site,respectively. Three-dimentional protein model and amino acids interaction were analyzed with Swiss-PdbViewer software.

RESULTS

The PC: A and PC: Ag of the proband were decreased to 46% (reference range: 70%-130%) and 50% (referencerange:70%-140%), respectively. Her grandmother,aunt, cousin and younger brother also showed declined PC:A and PC:Ag by approximately 50%. Genetic analysis revealed that the above individuals have all carried a deletional mutation c.1212-1212delG (p.Met364TrpfsX15) in exon 9 of the PROC gene which can cause replacement of Methionine at position 364 by Tryptophan and alteration of 15 downstream amino acids, and produce a premature stop codon at position 378. The score of MutationTaster was 1.000, indicating that the variant is pathogenic. Conservative analysis showed that the 15 altered amino acids are located in a conserved region across nine homologous species. Protein model analysis showed that the mutation has disrupted a catalytic domain of protein C thereby affected its function.

CONCLUSION

The heterozygous c.1212-1212delG deletional mutation in exon 9 of the PROC gene, which was unreported previously,probably accounts for the decrease of PC:A and PC:Ag in this pedigree.

Severe Protein C Deficiency due to Novel Biallelic Variants in PROC and Their Phenotype Correlation

Severe protein C deficiency due to biallelic PROC mutations is an extremely rare thrombophilia, most commonly presenting during the neonatal period as purpura fulminans. Despite treatment, severe morbidity and mortality are frequent. The current study reports 3 unrelated patients harboring novel homozygous PROC mutations and their clinical phenotypes. We discuss how the cytoprotective activity of protein C and its role in the stabilization of endothelial barriers may account for the unique symptoms of this thrombophilia.

Recommendations for clinical laboratory testing for protein C deficiency, for the subcommittee on plasma coagulation inhibitors of the ISTH

Inherited protein C (PC) deficiency increases risk of venous thromboembolism (VTE) by 5 to 10-fold in thrombosis-prone families; however, heterozygous PC deficiency alone does not determine that a subject has thrombophilia. Protein C deficient subjects, who lack additional inherited risk factors such as factor V Leiden or have no major acquired risk factors, may not suffer from VTE. In addition, PC deficiency may be acquired, often due to vitamin K antagonist treatment or liver disease. In contrast, homozygous or compound heterozygous PC deficiencies are rare and serious disorders, and affected infants are often in families with no history of PC deficiency or thrombosis. Laboratories commonly use the chromogenic PC assay to diagnose deficiency. Chromogenic assay is recommended due to its good specificity, but this assay fails to detect the rare type 2b deficiency where the defect is due to poor interaction with calcium ions, phospholipid, protein S, and factor Va and factor VIIIa. The clotting-based assay of PC is capable of detecting type 2b deficiency but it has reduced specificity. Importantly, PC level varies with age, adult reference ranges cannot be applied to babies or children and levels may not reach those of adults even in adolescence. Pre-analytical variables in the specimen affect measurement of PC, and can be assay-dependent; for example, a partially clotted sample will have falsely raised PC level by chromogenic assay but reduced level by clotting-based assay. Direct oral anticoagulants falsely raise PC level in the clotting-based assay but the standard chromogenic assay is unaffected.

Colonic Perforation in a Term Newborn with Hereditary Protein C Deficiency

We describe a term infant who experienced recurrent apnea associated with intracranial hemorrhage and later, developed colonic perforation. Plasma protein C activity was below detectable limits and a heterozygous PROC mutation was identified. Neonatal colonic perforation is rare, and this case report highlights the importance of considering congenital Protein C deficiency.

Significance of a Family-based Study of Hereditary Thrombosis: A Single-family Case Series of Protein C Deficiency

Thrombophilia is a serious unpredictable complication caused by gene mutations, resulting in anticoagulant deficiencies. We herein report a single-family case series of protein C (PC) deficiency. Case 1 involved a Japanese man whose PC deficiency resulted in severe systemic thrombosis. The patients in cases 2 and 3 were his daughters who were diagnosed with PC deficiency via carrier screening in 2001 and later both became pregnant. Owing to appropriate treatments during pregnancy, they did not develop thrombosis and safely gave birth to healthy infants. This family case series suggests that appropriate knowledge concerning thrombophilia helps prevent future emergencies.