Laboratory screening of thrombophilia. Evaluation of the diagnostic efficacy of a global test to detect congenital deficiencies of the protein C anticoagulant pathway

Clinical laboratories are at present confronted with increasing demands for thrombophilia work-up, which may seriously overwhelm their capacity. Recently, methods able to investigate the protein C anticoagulant pathway globally have been proposed. In this study we investigated the reliability of one such method for its ability to detect patients with known defects of the pathway by testing plasmas from patients with the FVQ506 mutation, with congenital protein C, protein S or antithrombin deficiencies, and patients with previous history of thrombosis, but no identifiable defects. The results show that the new global test fulfils the requirements for congenital protein C deficiency and activated protein C resistance associated with the FVQ506 mutation, which account for more than half of the congenital defects found in thrombophilia. However, congenital protein S deficiency very often remains undetected by this test. Improvement of sensitivity toward this component of the protein C anticoagulant pathway would enroll the global test as a suitable candidate to explore the pathway. Since antithrombin, which also remains undetected by this test, is an additional important risk factor for venous thrombosis, devoting time and effort to developing global tests able to detect defects in both the antithrombin and protein C pathways is warranted.

Three novel PROC gene lesions causing protein C deficiency

Missense mutations, three of them novel (Asn210-->Val, Asn248-->Ile, Ala355-->Val), were found in the protein C (PROC) genes of 7 patients with inherited protein C deficiency associated with venous thrombosis. Comparison with the phenotypic effects of mutations in the analogous residues of factor IX causing haemophilia B and the use of molecular modelling has provided explanations as to how these lesions might alter either the structure, function or secretion of the protein C molecules encoded.

An unknown genetic defect increases venous thrombosis risk, through interaction with protein C deficiency

We used two-locus segregation analysis to test whether an unknown genetic defect interacts with protein C deficiency to increase susceptibility to venous thromboembolic disease in a single large pedigree. Sixty-seven pedigree members carry a His107Pro mutation in the protein C gene, which reduces protein C levels to a mean of 46% of normal. Twenty-one carriers of the mutation and five other pedigree members had verified thromboembolic disease. We inferred the presence in this pedigree of a thrombosis-susceptibility gene interacting with protein C deficiency, by rejecting the hypothesis that the cases of thromboembolic disease resulted from protein C deficiency alone and by not rejecting Mendelian transmission of the interacting gene. When coinherited with protein C deficiency, the interacting gene conferred a probability of a thrombotic episode of approximately 79% for men and approximately 99% for women, before age 60 years.

[Type I protein C deficiency caused by a novel protein C gene mutation]

OBJECTIVE

To study the phenotype and genotype of a thrombophilia family.

METHODS

Antigens and activities of protein C, antithrombin III, protein S, plasminogen and activated protein C resistance were assayed in 13 members from four generations of the family.

RESULTS

Type I protein C deficiency was revealed in 5 members including the 3 members with deep vein thrombosis. All the exons and intron/exon junctions of the protein C gene were amplified by PCR. No abnormal band was found in SSCP assay. DNA sequencing identified a novel mutation 3444C-->A in exon VI of protein C gene leading to His134Asn. This mutation erased a Hph I site. PCR/Hph I analysis demonstrated that 6 members including 5 protein C deficiency members had the same mutations.

CONCLUSION

His134Asn is a novel mutation causing type I protein C deficiency.

Genetic markers: genes involved in thrombosis

This article summarizes the genetic markers of human venous and arterial thrombotic disorders. For venous thromboembolism, a factor V mutation (Arg 506-->Gln) has the highest risk, followed by protein C, S and antithrombin III gene defects. By contrast, these genetic defects are not associated significantly with arterial atherothrombotic disorders. Instead, a glycoprotein IIIa polymorphism (Pro33 versus Leu 33) has been reported to be associated with myocardial infarction. Fibrinogen Bbeta chain, factor VII, and plasminogen activator inhibitor-1 gene polymorphisms have been reported to influence the plasma levels of these factors and may indirectly be risk factors for arterial thrombotic disorders. Further studies will uncover additional genetic markers for thrombosis.