Gene Mutations in 21 Unrelated Cases of Phenotypic Heterozygous Protein C Deficiency and Thrombosis

Protein C deficiency (a novel mutation: ala291Thr) with systemic lupus erythematosus leads to the deep vein thrombosis

: The current study aims to explore the phenotype and genotype of a mutation Ala291Thr, which responsible for type I protein C (PC) deficiency in a Chinese woman. The PROC antigen was tested with chromogenic substrate method. PROC gene were amplified by PCR with direct sequencing. Bioinformatics and model analysis were used to study the harm of the mutation. PC activity (PC: A) levels of three members were reduced to 39, 57 and 56%, respectively, PC: antigen was decreased parallelly same as PC: A. Sequencing analysis showed proband with a novel heterozygous c.997G>A point mutation in exon 9 of PROC gene resulting in Ala291Thr. The Ala291Thr mutation is responsible for the decrease of PC: A, which is cross-reacting material negative deficiency and the first reported in the world. This mutation alone may not have significant clinical symptoms, whereas it will cause deep vein thrombosis when combined with systemic lupus erythematosus.

Recurrent superficial venous thrombophlebitis because of mutations in the protein C and fibrinogen genes in a young Argentinian female

: Hypodysfibrinogenemia and protein C deficiency are coagulopathies and in this report, we describe a young patient with both defects confirmed by molecular genetic tests. The patient was a 24-year-old woman referred for recurrent thrombophlebitis and finally deep venous thrombosis. Routine coagulation studies revealed mild decrease of protein C (0.49 IU, reference values 0.7-1.40 IU) and hypodysfibrinogenemia (0.88 g/l and 1.83 g/l for activity and antigen, respectively, reference values 2.0-4.0 g/l). Direct sequencing analyses were performed on FGA, FGB, and FGG genes to confirm hypodysfibrinogenemia and on the protein C gene to confirm protein C deficiency. As a result, the patient was shown to be heterozygous p.Ala82Gly in the FGG gene (Fibrinogen Dunedin) and for compound heterozygous missense mutation in protein C gene. To our knowledge, this is the first report on a case of combined dysfibrinogenemia and protein C deficiency confirmed by molecular genetic tests.

Familial thrombotic risk based on the genetic background of Protein C Deficiency in a Portuguese Study

INTRODUCTION

Inherited protein C (PC) deficiency is a well-known risk factor for venous thrombosis (VT). Plasma PC levels are reliable in moderate to severe deficiencies; however, in mildly deficient individuals, the levels may overlap with those considered normal. Genetic studies of PROC, which encodes PC, could help identify carriers; genome-wide association studies (GWAS) have shown that approximately 50% of phenotypic variation in PC deficiency is caused by the cumulative effects of mutations in several other loci, namely in the PROCR.

PATIENTS AND METHODS

With the main objective of determining the genotype/phenotype correlation in 59 Portuguese individuals from 26 unrelated families with history of thrombosis and repeatedly low/borderline PC plasma levels, we conducted a molecular study by direct sequencing of PROC; PROC promoter haplotypes and PROCR c.4600A>G polymorphism (rs867186), which are known to influence plasma PC concentrations, were also screened.

RESULTS

Twelve different PROC mutations were identified, one of them not previously reported, p.Cys105Arg. The mutation types and locations as well as haplotype combinations correlated with the phenotypic severity. The most frequent mutation, p.Arg199X, correlated with the CGTC haplotype and was identified in nine families containing patients with higher numbers of VT episodes. This mutation in homozygous individuals for the CGTC haplotype is a significant risk factor for VT in Portuguese.

CONCLUSION

These genetic family studies allowed the identification of the unknown carriers and individuals at a higher thrombotic risk within each family, thus permitting the evaluation of the need for prophylactic measures, particularly in at-risk situations.

Issues concerning the laboratory investigation of inherited thrombophilia

Inherited thrombophilia, defined as an increased familial tendency to develop thrombosis, may be due to congenital deficiencies or abnormalities of antithrombin, protein C or protein S; to the presence of a point mutation in the factor V gene (G1691A, factor V Leiden) leading to a poor anticoagulant response to activated protein C; or to the presence of a mutation in the prothrombin gene (G20210A) leading to increased plasma levels of prothrombin. The laboratory investigation of inherited thrombophilia should be limited to patients with a history of venous thromboembolism and, if positive, to their family members even though they are still asymptomatic. There is no indication for indiscriminate screening of the general population or screening of asymptomatic women before prescribing oral contraceptives. Testing should be based on the phenotype for antithrombin, protein C and protein S; on the phenotype and genotype (factor V Leiden mutation) for activated protein C resistance; and on the genotype (G20210A mutation) for hyperprothrombinemia. Phenotypic testing should be performed no sooner than three months after acute thrombotic events and at least 2 weeks after discontinuation of oral anticoagulant treatment.

A Survey of Left-handed Helices in Protein Structures

All naturally occurring amino acids with the exception of glycine contain one or more chiral carbon atoms and can therefore occur in two different configurations, L (levo, left-handed) and D (dextro, right-handed). Proteins are almost exclusively built from L-amino acids. The stereochemical bias of nature is further reflected at the secondary structure level where right-handed helices are strongly preferred over left-handed helices. The handedness of helices has not received much attention in the past and is often overlooked during the analysis, description and deposition of experimentally solved protein structures. Therefore, an extensive survey of left-handed helices in the Protein Data Bank (PDB) was undertaken to analyse their frequency of occurrence, length, amino acid composition, conservation and possible structural or functional role. All left-handed helices (of four or more residues) in a non-redundant subset of the PDB, were identified using hydrogen-bonding analysis, comparison of related structures, and experimental electron density assessment to filter out likely spurious and artefactual hits. This analysis yielded 31 verified left-handed helices in a set of 7284 proteins. The phi angles of the residues in the left-handed helices lie between 30 degrees and 130 degrees and the psi angles lie between -50 degrees and 100 degrees . Most of the helices are short (four residues) and for 87% of them, it was possible to determine that they are important for the stability of the protein, for ligand binding, or as part of the active site. This suggests that, even though left-handed helices are rare, when they do occur, they are structurally or functionally significant. Four secondary structure assignment programs were tested for their ability to identify the handedness of the helices. Of these programs, only DSSP correctly assigns the handedness.