1. The Subcommittee completed two activities in the past year which resulted in Official Communications. One is a database of mutations of antithrombin published in Thrombosis and Haemostasis 77, 197-211, as "Antithrombin Mutation Database 2nd (1997) Update." The other, "Protein S Deficiency: A Database of Mutations," is currently in press in Thrombosis and Haemostasis.

2. We had a full-day meeting on Saturday with about 450 attendees and the meeting room was always full to overflowing. The meeting adjourned at 4:40 p.m.

3. 3. This year's meeting consisted of six sessions and a total of 17 papers were presented.

   The contents of the session are as follows:

   Protein S Deficiency

   Six papers were presented and the first two were about the assay of free protein S in plasma. The next four papers were on the genetic and phenotypic characterizations of type I and type III protein S deficiency, paying attention to their nomenclature and classification, in particular.

   Dr. B. Dahlback (Sweden) introduced a new method of assay of free protein S that is fast, reproducible and highly specific for free protein S. The principle of this method is called ELSA ( Enzyme-linked Ligand Sorbent Assay), which utilizes C4BP as immobilized ligand for catching free protein S in plasma.

   Next, Dr. J. Amiral (France) reported the results of the measurement of free and total protein S and protein S activity in 520 healthy individuals. He emphasized that cholesterol and BMI (body mass index) are major parameters affecting the total protein S assay, that gender and cholesterol are parameters affecting the free protein S assay, and that gender and BMI are parameters affecting protein S activity. He also emphasized that the lower threshhold for the diagnosis of hereditary protein S deficiency should be carefully determined in subpopulations of normal subjects which include males, females, and females using oral contraceptives.

   The subsequent four papers dealt with protein S gene mutations.

   Dr. R.E. Simmonds (U.K.) examined a large protein S-deficient kindred (122 germline individuals including 44 affected) and identified Gly295 to Val mutation in three family members. He concluded that the type I (low total protein S antigen and low free protein S antigen) and type III (normal total protein S antigen and low free protein S antigen) protein S deficiencies are phenotypic variants of the same genetic disorder and arose because of an age-related increase of total protein S antigen levels.

   Dr. T. Yamazaki (Japan) also issued the same conclusion from a study on two protein S deficient families in Japan.

   Dr. N. Sala (Spain) also reported results of the genetic analysis of families with type I and/or type III protein A deficiency which demonstrated the complexity underlying type III deficiency. It concluded that while allelic heterogeneity in the protein S (PROS1) gene is the main cause of type I protein S deficiency, type III or free protein S deficiency is likely to be a genetically heterogeneous or complex disease. Free protein S deficiency results either from a mutation in a single major gene like PROS1, or it results from the interaction of different factors, among which the protein S Heerlen allele seems to play a role.

   In the last paper, Dr. R. Bertina (Netherlands) discussed protein S Heerlen allele. He concluded that, in spite of reduced levels of free protein S in individuals with protein S Heerlen allele, this allele is not associated with a risk factor for thrombosis. At the end of the session, the subcommittee chairman proposed to organize a new working party on protein S deficiency which would concern assay of free protein S and nomenclature of type I and type III deficiencies.

   Protein C Deficiency

   Dr. R.A. Marlar stated that a report of the Working Party on the Clinical Aspects and Treatment of Homozygous Protein C and Protein S Deficiencies is being prepared for submission to Thrombosis and Haemostasis as an official SSC communication.

   Antithrombin

   Dr. E. Gray (U.K.) reported the result of the Collaborative Study for the Second International Standard for Antithrombin Concentrate. An international collaborative study including 18 laboratories in ten countries was organized. The proposed Second International Standard, 96/520, was calibrated against the First International Standard for Antithrombin, Concentrate, 88/548, and also compared against the Second International Standard for Antithrombin, Plasma, 93/768, by both functional assays and antigen methods. As a result, based on the means of all assays against the First International Standard for Antithrombin, Concentrate, the overall respective functional and antigenic potencies for the candidate preparation, 96/520, were shown to be 4.7 IU/ampoule and 5.1 IU/ampoule. This result will be published soon as an official publication of the subcommittee.

   Dr. S.C. Bock (U.S.) reported that antithrombin-beta, the quantitatively minor isoform in blood, may account for a substantial portion of antithrombin activity in the vessel wall.

   Dr. V. Picard (France) reviewed a database of anti-serpin antibodies. He suggested that anti-serpin antibodies are particularly useful in structure-function studies of serpins since they can specifically react with a given conformation, showing several examples of monoclonal antibodies against either antithrombin, C1-inhibitor or PAI-1.

   Thrombomodulin gene mutations

   Thrombomodulin (TM) is an integral endothelial cell membrane protein that functions as a cofactor in the thrombin-mediated activation of the protein C anticoagulant pathway. It has been suggested that an impaired TM cofactor function also could constitute a pro-thrombotic abnormality leading to thromboembolic disease. Dr. A.K. Ohlin (Sweden) presented the data of TM gene mutation in a patient with venous thromboembolic disease and showed that a defect in the TM gene leads to familial thrombophilia. Dr. H. Ireland (U.K.) also discussed TM gene mutations associated with myocardial infarction and suggested that mutations in the promoter region of the thrombomodulin gene may constitute a risk for arterial thrombosis.

   TFPI (Tissue Factor Pathway Inhibitor)

   Two papers on TFPI were presented. First, Dr. S.P. Bajaj (U.S.) discussed correlation of the plasma levels of TFPI with various diseases. TFPI is present as free form and lipoprotein-associated form in plasma and also as endothelial cell-associated form on vascular walls. Dr. H. Kato (Japan) introduced the newly developed EIA system which uses polyclonal and monoclonal antibodies against recombinant TFPI to measure free form TFPI and total TFPI in plasma. He also compared two commercially

   available kits for the measurement of TFPI now available from Kaketsuken in Japan and from American Diagnostic Corporation. He showed that total TFPI was highly correlated (r=0.87) between the two kits; however, the correlation of free form TFPI was not correlated well between the two kits (r=0.60).

   APC-Resistance

   APC-resistance has been discussed at the last three meetings of the subcommittee; therefore, at this year's meeting only three papers were presented. The final one by Dr. A. Tripodi was a summary of the past discussion and a proposal for a Working Party on the Standardization of the APC-Resistance Test. At the end, the chairman suggested possible members of the working party. The preceding presentations were "Cost-benefit analysis for screening of APC-resistance" by Dr. W. Schramm (Germany) and "Factor V 506Q: Prevalence, thrombotic risk and risk modifiers" by Dr. J.P. Miletich (U.S.)

   Dr. Schramm discussed the risk of venous thromboembolic events in oral contraceptive users with and without APC-resistance. He showed that the incidence was 17.3 and 1.8, respectively, per 10,000 person-year, whereas, the incidence of venous thromboembolic events in oral contraceptive non-users with and without APC-resistance were 7.2 and 1.6, respectively, per 10,000 person-year. From this survey, he suggested that although testing of new oral contraceptive users, with and without exclusion by family history of venous thromboembolic events, seems to be less cost-effective than previously reported, screening does seem to be a rational use of scarce health care resources.

   Dr. Miletich discussed prevalence, thrombotic risk and risk modifiers of factor V 506Q allele, which is the only genetically evidenced cause for APC-resistance, from a huge survey including 2,312 men from the Physicians' Health Study and 2,439 women from the Women's Health Study. From the Physicians' Health Study, he concluded that teterozygosity for the mutated allele does not detectably alter the probability of heart attack or stroke but does increase the chance for first-event venous thromboembolism about four-fold. He also showed that the mutated allel was found with similar frequency among men and women but is significantly different among ethnic groups, i.e., the carrier frequency was 5.3%, 2.2%, 1.2%, 0.5% and 1.3% in Caucasian, Hispanic, African, Asian, and Native Americans, respectively. Finally, he surprised the attendees by showing that the calculated number of heterozygous carriers is estimated to be more than 11 million among Americans and more than 423,000 are likely to be women who use oral contraceptives.

4. Two new working parties were organized during the meeting:

   1. Working Party on the Standardization of the APC-Resistance Test, APC-Resistance Assay Method, Expression of the Results, Diagnosis of Factor V Leiden, and Other Causes of APC-Resistance

   2. Working Party on Protein S Deficiency: Assay Method of Free Protein S in Plasma and Nomenclature of Types I and III

5. The following reports will be issued soon as official SSC communications of the subcommittee:

   1. Report on the International Collaborative Study for the Second International Standard for Antithrombin Concentrate

   2. Report of the Working Party on the Clinical Aspects and the Treatment of Homozygous Protein C and Protein S Deficiencies

Table of Contents.