We have examined the prothrombin gene as a candidate gene for venous thrombosis in selected patients with a documented familial history of venous thrombophilia. All the exons and the 5′- and 3′-UT region of the prothrombin gene were analyzed by polymerase chain reaction and direct sequencing in 28 probands. Except for known polymorphic sites, no deviations were found in the coding regions and the 5′-UT region. Only one nucleotide change (a G to A transition) at position 20210 was identified in the sequence of the 3′-UT region. Eighteen percent of the patients had the 20210 AG genotype, as compared with 1% of a group of healthy controls (100 subjects). In a population-based case-control study, the 20210 A allele was identified as a common allele (allele frequency, 1.2%; 95% confidence interval, 0.5% to 1.8%), which increased the risk of venous thrombosis almost threefold odds ratio, 2.8; 95% confidence interval, 1.4 to 5.6. The risk of thrombosis increased for all ages and both sexes. An association was found between the presence of the 20210 A allele and elevated prothrombin levels. Most individuals (87%) with the 20210 A allele are in the highest quartile of plasma prothrombin levels (> 1.15 U/mL). Elevated prothrombin itself also was found to be a risk factor for venous thrombosis.

A deficiency of protein C (PC), antithrombin, or protein S is strongly associated with deep-vein thrombosis in selected patients and their families. However, the strength of the association with venous thrombosis in the general population is unknown. This study was a population-based, patient-control study of 474 consecutive outpatients, aged less than 70 years, with a first, objectively diagnosed, episode of venous thrombosis and without an underlying malignant disease, and 474 healthy controls who matched for age and sex. Relative risks were estimated as matched odds ratios. Based on a single measurement, there were 22 (4.6%) patients with a PC deficiency (PC activity, less than 0.67 U/mL or PC antigen, less than 0.33 U/mL when using coumarins). Among the controls, the frequency was 1.5% (seven subjects). Thus, there is a threefold increase in risk of thrombosis in subjects with PC levels below 0.67 or 0.33 U/mL [matched odds ratio, 3.1; 95% confidence interval (CI), 1.4 to 7.0]. When a PC deficiency was based on two repeated measurements, the relative risk for thrombosis increased to 3.8 (95% CI, 1.3 to 10); when it was based on DNA-confirmation, the relative risk increased further to 6.5 (95% CI, 1.8 to 24). In addition, there was a gradient in thrombosis risk, according to PC levels. The results for antithrombin are similar to those for PC, although less pronounced (relative risk, 2.2; 95% CI, 1.0 to 4.7). We could not find an association between reduced total protein S (relative risk, 0.7; 95% CI, 0.3 to 1.8) or free protein S levels (relative risk, 1.6; 95% CI, 0.6 to 4.0) and thrombosis risk. Although not very frequent, PC and antithrombin deficiency are clearly associated with an increase in thrombosis risk.

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SummaryReported prevalence rates for protein C (PC) deficiency in the population at large have varied widely. The differences presumably reflect the existence of an apparently high number of clinically recessive forms of the deficiency. In an attempt to document more precisely the prevalence of PC deficiency in the healthy population we have measured PC activity in just under 10,000 blood donors in the West of Scotland. After repeat testing of donors with low results and then further observation and selection, 32 donors were identified who had individual mean PC activities below the age- and gender-specific study reference range. Assessment of available first degree relatives, and also PC gene analysis in 23 of these donors, allowed identification of at least 14 with an inheritable deficiency (8 by both family study and gene analysis, 3 by family study alone and 3 by gene analysis alone). Two recurring and seven unique point mutations, only one of which has been previously described, were identified. The observed prevalence of inherited PC deficiency was 1.45 per 1000 (95% Cl, 0.79/1000 to 2.43/1000). However after correcting for the possibility of missing some genuine inherited deficiencies we estimated the prevalence to be as high as 1 in 500. All cases of hereditary deficiency were asymptomatic with regard to thrombosis and none had a strong family history of thrombosis. These findings confirm the rather frequent occurrence of asymptomatic individuals with PC deficiency and support the hypothesis that additional defects in the anticoagulant pathways may be required to confer a high-thrombotic-risk phenotype.

Protein C deficiency (McK. No. 176860) is an autosomally inherited disorder that is associated with a high risk of recurrent venous thrombosis. Until recently, the analysis and diagnosis of protein C deficiency has been reliant upon the laboratory measurement of plasma protein C antigen and activity levels. Diagnostic uncertainty ffioy, however, arise due to the overlap between the ranges of values characteristic of the normal and deficiency states. Diagnostic uncertainty may be further increased if the patient is already undergoing ordl anticoagulant therapy with vitamin K antagonists such as Coumarin drugs that block y-carboxylation. Moreover, this type of laboratory analysis provides little or no information as to the nature of the underlying defect or its mode of inheritance. The utility of a molecular genetic approach to the study of protein C deficiency lies in its ability to provide accurate and reliable information both on the specific genetic lesion(s) involved and on the genotypes of the propositae and their relatives. Precise knowledge of the underlying genetic abnormalities may also provide starting points for the structure-function analysis of the protein C gene (the effect of promoter mutations on gene expression) and molecule (protein C variants). With the advent of rapid and efficient techniques for the analysis of DNA at the single nucleotide level, such an approach has become feasible in an increasing number of laboratories. Here, we present an up-todate listing of mutations in the protein C gene so far identified. Only a small proportion of these lesions have been published in any detail. All unreviewed and unpublished data must be regarded as preliminary. Inclusion in the database should not preclude more detailed publication elsewhere. Structure and Function of Protein C Protein C, a vitamin K-dependent glycoprotein and zymogen of a serine protease, plays an important regulatory role in haemostasis (1, 2). Synthesized in the liver as a single-chain polypeptide, it undergoes post-translational modification (B-hydroxylation, y-carboxylation and glycosylation) to give rise