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Coagulation factor V gene mutation associated with activated protein C resistance leading to recurrent thrombosis, leg ulcers, and lymphedema: successful treatment with intermittent compression
Coagulation factor V gene mutation associated with activated protein C resistance leading to recurrent thrombosis, leg ulcers, and lymphedema: successful treatment with intermittent compression Dominik Peus, MD, a Sherko v. Schmiedeberg, MD, a Andreas Pier MD, a Rtidiger E. Scharf, MD, c Armr Wehmeier, MD, b Thomas Ruzicka, MD, a and Jean Krutmann, MD a Diisseldorf Germany Activated protein C resistance is the most frequent cause of venous thrombosis. We describe a patient with extensive ulcerations and severe lymphedema of the legs after recurrent thrombosis. Laboratory tests revealed a pathologic activated protein C resistance and a reduced functional protein S. The underlying genetic defect was identified as a heterozygous coagulation factor V mutation. A combined therapeutic approach of intermittent compression, repeated debridements and systemic antibiotics resulted in marked improvement of both lymphedema and leg ulcers. (J Am Acad Dermatol 1996;35:306-9.) Deep venous thrombosis is often associated with a predisposing factor such as surgery, trauma, child2 birth, or neoplasm. I' 2 However, in some patients in whom thrombosis occurs without an apparent cause, a coagulation defect may be responsible. Several of these defects have been identified,3-7 some of which are genetically determined. Those are deficiencies of protein C, protein S, and antithrombin 1II and dysfibrinogenemia.8 Recently, an inherited defect in the anticoagulant response to activated protein C was described and subsequently termed activated protein C (APC) resistance.9 Protein C, a vitamin K-dependent plasma protein, plays a key role in the anticoagulant system, m-12 Protein C is activated by a complex of thrombin with thrombomodulin. APC inhibits coagulation by inactivating coagulation factors Va and VIIIa. 13 It also stimulates fibrinolysis.TM
This article is made possible through an educational grant from the Dermatolo~cal Division, O1~o Pharmaceutical Corporation. From the Department of Dermatology,a the Department of Hematology,b and the Institute for Haemostasis and Transfusion Medicine,c Hemrich-Heine-University, Dfisseldorf. Dominik Peus is supported by a grant (PE 635/1-1) from the Deutsche Forschungsgemeinschaft (DFG). Reprint requests: Dominik Peus, MD, Deparmaent of Dermatology, Mayo Clinic, Gugg. 442D, Rochester, MN 55905. ORTHO
Copyright © 1996 by the American Academy of Dermatology, Inc. 0190-9622/96 $5.00 + 0
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Protein S is an important anticoagulant plasma protein that is vitamin K-dependent and functions as a cofactor to APC in the degradation of factors Va and VIga. is In human plasma, protein S exists as free protein S and in complex with C4b-binding protein. 16 Only free protein S can act as cofactor to APC. 17 Hereditary deficiency of protein S is a cause of familial thrombosis) 8 We describe a patient with recurrent deep venous thrombosis caused by a pathologic APC resistance. The patient had severe lymphedema and extensive leg ulcers. CASE REPORT
A 47-year-old man had severe lymphedema and extensive ulcers of the legs and feet. The swelling had begun 4 weeks before his ulcerations enlarged. He had had multiple superficial and deep venous thromboses, starting at the age of 30. For the last 17 years he had intermittent chronic ulcers of the legs. Secondary infections and subsequent lymphedema developed. The patient was not diabetic and was taking no medications. There was no history of trauma and no family history of thrombosis. Examination revealed severe lymphedema of the legs, with elephantiasis-like swelling of the feet and toes (Fig. 1). There were extensive ulcers over the medial and lateral malleoli, and both feet were superinfected (Fig. 2). Phlebography revealed a severely impaired superficial and deep venous system in both legs caused by nonfunctional venous valves compatible with recurrent venous thrombosis. Arteriography showed a normal arterial sys-
Jottrnal of the American Academy of Dermatology Volume 35, Number 2, Part 2
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307
Fig. 1. Intermittent compression treatment oflymphedema. A, Massivesecondarylymphedema and eXtensive ulcerations of both feet before treatment. B, Reduction of circumference of both lower legs of over 14 cm after 2 days of intermittent compression. tern with loss of peripheral arterioles in several toes. Arterial pulses were normal. Coagulation tests revealed a pathologic APC resistance ratio of 1.8 (normal value: 2 to 5) (Coatest, Chromogenix, M61ndal, Sweden) and a reduced functional protein S of 18% (normal value: 70% to 140%). Total and free protein S were normal. Functional protein C, protein C antigen, and all other coagulation factors were within normal limits. By means of polymerase chain reaction modified from the method of Bertina et al.,19 a heterozygous coagulation factor V mutation was detected. For treatment, automated intermittent compression (Lympha-mat gradient®, B6sl, Aachen, Germany) was applied 3 to 4 times daily for 20 to 30 minutes. Within 2 days the circumference of the leg was reduced by 14 cm (Fig. 1). For several weeks antibiotics were administered, debridements were repeatedly performed, and mesh grafts were appfied to ulcers. Because of necrotic changes on the tip of the left second toe, amputation was necessary. Complete heating of most ulcers was achieved within 3 months. Because of the coagulation defect, lowdose heparin (Fraxiparin) 0.3 ml was subcutaneously administered once daily. Before discharge the patient was given phenoprocoumon (Marcumar) and maintained at an international normalized ratio value of 2 to 3. With this therapy and intermittent compression as required, the patient has not developed any new ulcers. DISCUSSION Venous thrombosis occurs in association with a variety of risk factors, a° In our patient, recurrent su-
perficial and deep venous thromboses without an obvious precipitating cause began at age 30. This history suggests a coagulation defect. Recurrent deep venous thrombosis caused by a hypercoagulable state can lead to venous insufficiency that m a y give rise to edema, stasis, and ulcers of the lower extremities. 21 However, cutaneous necrosis that frequently develops in patients with congenital protein C deficiency who are beginning warfarin therapy 22 was recently described in a pregnant w o m a n secondary to APC resistance in hereditary angioedema. 23 An increasing number of inherited coagulation defects has been identified and account for approximately 10% o f cases o f venous thrombosis. 24,25 Resistance to APC is at least 10 times more c o m m o n than any other known genetic defect. 26 This defect accounts for thrombosis in 20% to 30% o f unselected patients 9,27 and in about 50% o f patients with a family history of thrombosis. 28 In our patient, resistance to APC was detected by the APC-resistance test, in which clotting times are measured in the presence and absence o f exogenous APC. 26 As resistance to A P C is associated with a sevenfold increased risk o f deep venous thrombosis, and because all other coagulation parameters were normal apart from a reduced functional protein S, resistance to APC was most likely a major contributing factor for recurrent thrombosis in our patient.
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Journal of the AmericanAcademyof Dermatology August 1996
Fig. 2. Extensive ulcers of left forefoot. A, Before treatment. B, After treatment.
A decrease of functional protein S, along with normal total and flee protein S antigen, was repeatedly observed in our patient. A possible explanation is a molecular abnormality of protein S that could not be recognized by the immunologically based tests used to determine total and free protein S antigen. This is unlikely, however, because it requires coincident mutations of the protein S and factor V genes rather than a single factor V mutation. More likely, the decreased functional protein S does not reflect tree protein S deficiency, but interference in the assay by APC resistance. 29 Accordingly, Faioni et al.30 found a high concordance of APC resistance with reduced protein S levels in persons with resistance to APC. APC resistance may be misdiagnosed as inherited functional protein S deficiency.31 Once resistance to APC was diagnosed in our patient, polymerized chain reaction was employed to identify a heterozygous coagulation factor V mutation. In most cases APC resistance is caused by a single point mutation in the coagulation factor V gene.32, 33 This mutation predicts the replacement of Arg506 with Gin. 19 As Arg506 is located at one of the APC cleavage sites of factor Va, the mutated factor Va is less sensitive to APC-mediated inactivation. 34 A single amino acid exchange causes factor V resistance to proteolysis by APC. 35 This mutation, which is thought to have an autosomal mode of inheritance,26 is the single most prevalent genetic defect associated with thrombosis
and may affect 3% to 7% of the general population. 36 Whereas the relative risk is increased 80-fold for homozygous persons, 37 it is increased sevenfold in heterozygous persons, 9 which is consistent with the history of recurrent thrombosis in our patient. However, in light of the high incidence of this mutation in the general population, factor V gene mutation alone does not fully account for this patient's problems. Additional predisposing factors include progressive deterioration of the venous system and microvascular occlusive disease related to smoking. Secondary lymphedema in this patient was most likely due to recurrent infections along with superficial and deep venous insufficiency. Conventional compression therapy may not be sufficient to prevent further progression of disease when high-degree venous insufficiency and extensive lymphedema are present. In these cases intermittent compression can be employed. This treatment, in combination with antibiotic treatment, debridements, and mesh grafting, proved to be effective in our patient.
REFERENCES
1. Coon WW. Venous thromboembolism.Prevalence,risk factors, and prevention.Clin Chest Med 1984;5:391-401. 2. SchaferAI. The hypercoagulablestates. Ann Intern Med 1985;102:814-28. 3. Egeberg O. InheritedantithrombinlII deficiencycausing thrombophilia. Thromb Diathes Haemorrh 1965;13:51630.
Journal of the American Academy of Dermatology Volume 35, Number 2, Part 2
4. Griffin JH, Evatt B, Zimmerman TS, et al. Deficiency of protein C in congenital thrombotic disease. J Clin Invest 1981;68:1370-3. 5. Schwarz HP, Fischer M, Hopmeier P, et al. Plasma protein S deficiency in familial thrombotic disease. Blood 1984;64: 1297-1300. 6. Bithell TC. Hereditary dysfibrinogenemia. Clin Chem 1985;31:509-16. 7. Aoki N, Moroi M, Sakata Y, et al. Abnormal plasminogen: a hereditary molecular abnormality found in a patient with recurrent thrombosis. J Clin Invest 1978;61:1186-95. 8. Allaart CF, Briet E. Familial venous thrombophilia. In: Bloom AL, Forbes CD, Thomas DP, et al. editors. Haemostasis and thrombosis. Edinburgh: Churchill Livingstone, 1994:1349-60. 9. DahlNick B, Carlsson M, Svensson PJ. Familial thrombophilia due to a previously unrecognized mechanism characterized by poor anticoagulant response to activated prorein C: prediction of a cofactor to activated protein C. Proc Natl Acad Sci U S A. 1993;90:1004-8. 10. DahlbBack B, Stenflo J. The protein C anlicoagulant system. In: Stamatoyannopoulos G, Nienhuis AW, Majems PW, et al. editors. The molecular basis of blood diseases. Philadelphia: WB Saunders, 1994:599-628. 11. Walker FJ. Regulation of activated protein C by a new protein: a possible function for bovine protein S. J Biol Chem 1980;255:5521-4. 12. Esmon CT. The roles of protein C and thrombomodulin in the regulation of blood coagulation. J Biol Chem 1989; 264:4743-6. 13. Esmon CT. Protein-C: biochemistry, physiology, and clinical implications. Blood 1983;62:1155-8. 14. van Hinsbergh VW, Bertina RM, van Wijngaarden A, et al. Activated protein C decreases plasminogen activatorinhibitor activity in endothelial cell-conditioned medium. Blood 1985;65:444-51. 15. DahlNick B, Stenflo J. The protein C anticoagulantsystem. In StamatoyannoponiosG, Nienhuis AW, Majerus PW, et al. editors. The molecular basis of blood diseases. Philadelphia: WB Saunders, 1994:599-628. 16. Hillarp A, Dahlb~ickB. Novel subunit in C4b-bindingprotein required for protein S binding. J Biol Chem 1988;263: 12759-64. 17. Dahlb~ick B. Inhibition of protein Ca cofactor function of human and bovine protein S by C4b-bindingprotein. J Biol Chem 1986;261:12022-7. 18. Comp PC, Nixon PR, Cooper MR, et al. Familial protein S deficiency is associated with recurrent thrombosis. J Clin Invest 1984;74:2082-8. 19. Bertina RM, Koeleman BP, Koster T, et al. Mutation in blood coagulation factor V associated with resistance to activated protein C. Nature 1994;369:64-7. 20. Thomas DP. Pathogenesis of venous thrombosis. In: Bloom AL, Forbes CD, Thomas DP, et al. editors. Haemostasis and thrombosis. Edinburgh: Churchill Livingstone, 1994:1335-47. 21. Coffman JD. Cutaneous changes in peripheral vascular
Peus et al.
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23.
24.
25. 26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
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disease. In: Fitzpatrick TB, Eisen AZ, Wolff K, et al. editors. Dermatology in general medicine. New York: McGraw-Hill, 1993:2077-104. McGhee WG, Klotz TA, Epstein DJ, et al. Coumarin skin necrosis associated with hereditary protein C deficiency. Ann Intern Med 1984;100:59-60. Perkins W, Downie I, Keefe M, et al. Cutaneous necrosis in pregnancy secondary to activated protein C resistance in hereditary angioedema. J R Soc Med 1995;88: 229P-30P. Tabemero MD, Tomas JF, Alberca I, et al. Incidence and clinical characteristics of hereditary disorders associated with venous thrombosis. Am J Hematol 1991;36:249-54. Miletich JP, Prescott SM, White R, et al. Inherited predisposition to thrombosis. Cell 1993;72:477-80. Svensson PJ, Dahlb~ick B. Resistance to activated protein C as a basis for venous thrombosis. N Engl J Med 1994; 330:517-22. Koster T, Rosendaal FR, de Ronde H, et al. Venous thrombosis due to poor anticoagulantresponse to activated protein C: Leiden thrombophilia study. Lancet 1993;342: 1503-6. Hellgren M, Svensson PJ, Dahlb~ickB. Resistance to activated protein C as a basis for venous thromboembolism associated with pregnancy and oral contraceptives. Am J Obstet Gynecol 1995;173:210-3. D'Angelo SV, Mazzola G, Della Valle P, et al. Variable interference of activated protein C resistance in the measurement of protein S activity by commercial assays. 1994;77:375-8. Faloni EM, Franchi F, Asti D, et al. Resistance to activated protein C in nine thrombophilic families: interference in a protein S fimctional assay. Thromb Haemost 1993;70:106771. Cooper PC, Hampton KK, Makris M, et al. Further evidence that activated protein C resistance can be misdiagnosed as inherited functional protein S deficiency. 1994;88:201-3. Voorberg J, Roelse J, Koopman R, et al. Association of idiopathic venous thromboembolism with single point-mutation at Arg506 of factor V. Lancet 1994;343:1535-6. Greengard JS, Sun X, Xu X, et al. Activated protein C resistance caused by Arg506Gln mutation in factor Va. Lancet 1994;343:1361-2. Ztller B, DahlNick B. Linkage between inherited resistance to activated protein C and factor V gene mutation in venous thrombosis. Lancet 1994;343:1536-8. Sun X, Evatt B, Griffin JH. Blood coagulation factor. Va abnormality associated with resistance to activated protein C in venous thrombophilia. Blood 1994;83:3120-5. Dahlb~ick B. Inherited thrombophilia: resistance to activated protein C as a pathogenic factor of venous thromboembolism. Blood 1995;85:607-14. Rosendaal FR, Koster T, Vandenbroucke JP, et al. High risk of thrombosis in patients homozygous for factor V Leiden (activated protein C resistance). Blood 1995;85: 1504-8.
This article is made possible through an educational grant from the Dermatolo~cal Division, O1~o Pharmaceutical Corporation. From the Department of Dermatology,a the Department of Hematology,b and the Institute for Haemostasis and Transfusion Medicine,c Hemrich-Heine-University, Dfisseldorf. Dominik Peus is supported by a grant (PE 635/1-1) from the Deutsche Forschungsgemeinschaft (DFG). Reprint requests: Dominik Peus, MD, Deparmaent of Dermatology, Mayo Clinic, Gugg. 442D, Rochester, MN 55905. ORTHO
Copyright © 1996 by the American Academy of Dermatology, Inc. 0190-9622/96 $5.00 + 0
306
16/4/73492
Protein S is an important anticoagulant plasma protein that is vitamin K-dependent and functions as a cofactor to APC in the degradation of factors Va and VIga. is In human plasma, protein S exists as free protein S and in complex with C4b-binding protein. 16 Only free protein S can act as cofactor to APC. 17 Hereditary deficiency of protein S is a cause of familial thrombosis) 8 We describe a patient with recurrent deep venous thrombosis caused by a pathologic APC resistance. The patient had severe lymphedema and extensive leg ulcers. CASE REPORT
A 47-year-old man had severe lymphedema and extensive ulcers of the legs and feet. The swelling had begun 4 weeks before his ulcerations enlarged. He had had multiple superficial and deep venous thromboses, starting at the age of 30. For the last 17 years he had intermittent chronic ulcers of the legs. Secondary infections and subsequent lymphedema developed. The patient was not diabetic and was taking no medications. There was no history of trauma and no family history of thrombosis. Examination revealed severe lymphedema of the legs, with elephantiasis-like swelling of the feet and toes (Fig. 1). There were extensive ulcers over the medial and lateral malleoli, and both feet were superinfected (Fig. 2). Phlebography revealed a severely impaired superficial and deep venous system in both legs caused by nonfunctional venous valves compatible with recurrent venous thrombosis. Arteriography showed a normal arterial sys-
Jottrnal of the American Academy of Dermatology Volume 35, Number 2, Part 2
Peus et aL
307
Fig. 1. Intermittent compression treatment oflymphedema. A, Massivesecondarylymphedema and eXtensive ulcerations of both feet before treatment. B, Reduction of circumference of both lower legs of over 14 cm after 2 days of intermittent compression. tern with loss of peripheral arterioles in several toes. Arterial pulses were normal. Coagulation tests revealed a pathologic APC resistance ratio of 1.8 (normal value: 2 to 5) (Coatest, Chromogenix, M61ndal, Sweden) and a reduced functional protein S of 18% (normal value: 70% to 140%). Total and free protein S were normal. Functional protein C, protein C antigen, and all other coagulation factors were within normal limits. By means of polymerase chain reaction modified from the method of Bertina et al.,19 a heterozygous coagulation factor V mutation was detected. For treatment, automated intermittent compression (Lympha-mat gradient®, B6sl, Aachen, Germany) was applied 3 to 4 times daily for 20 to 30 minutes. Within 2 days the circumference of the leg was reduced by 14 cm (Fig. 1). For several weeks antibiotics were administered, debridements were repeatedly performed, and mesh grafts were appfied to ulcers. Because of necrotic changes on the tip of the left second toe, amputation was necessary. Complete heating of most ulcers was achieved within 3 months. Because of the coagulation defect, lowdose heparin (Fraxiparin) 0.3 ml was subcutaneously administered once daily. Before discharge the patient was given phenoprocoumon (Marcumar) and maintained at an international normalized ratio value of 2 to 3. With this therapy and intermittent compression as required, the patient has not developed any new ulcers. DISCUSSION Venous thrombosis occurs in association with a variety of risk factors, a° In our patient, recurrent su-
perficial and deep venous thromboses without an obvious precipitating cause began at age 30. This history suggests a coagulation defect. Recurrent deep venous thrombosis caused by a hypercoagulable state can lead to venous insufficiency that m a y give rise to edema, stasis, and ulcers of the lower extremities. 21 However, cutaneous necrosis that frequently develops in patients with congenital protein C deficiency who are beginning warfarin therapy 22 was recently described in a pregnant w o m a n secondary to APC resistance in hereditary angioedema. 23 An increasing number of inherited coagulation defects has been identified and account for approximately 10% o f cases o f venous thrombosis. 24,25 Resistance to APC is at least 10 times more c o m m o n than any other known genetic defect. 26 This defect accounts for thrombosis in 20% to 30% o f unselected patients 9,27 and in about 50% o f patients with a family history of thrombosis. 28 In our patient, resistance to APC was detected by the APC-resistance test, in which clotting times are measured in the presence and absence o f exogenous APC. 26 As resistance to A P C is associated with a sevenfold increased risk o f deep venous thrombosis, and because all other coagulation parameters were normal apart from a reduced functional protein S, resistance to APC was most likely a major contributing factor for recurrent thrombosis in our patient.
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Journal of the AmericanAcademyof Dermatology August 1996
Fig. 2. Extensive ulcers of left forefoot. A, Before treatment. B, After treatment.
A decrease of functional protein S, along with normal total and flee protein S antigen, was repeatedly observed in our patient. A possible explanation is a molecular abnormality of protein S that could not be recognized by the immunologically based tests used to determine total and free protein S antigen. This is unlikely, however, because it requires coincident mutations of the protein S and factor V genes rather than a single factor V mutation. More likely, the decreased functional protein S does not reflect tree protein S deficiency, but interference in the assay by APC resistance. 29 Accordingly, Faioni et al.30 found a high concordance of APC resistance with reduced protein S levels in persons with resistance to APC. APC resistance may be misdiagnosed as inherited functional protein S deficiency.31 Once resistance to APC was diagnosed in our patient, polymerized chain reaction was employed to identify a heterozygous coagulation factor V mutation. In most cases APC resistance is caused by a single point mutation in the coagulation factor V gene.32, 33 This mutation predicts the replacement of Arg506 with Gin. 19 As Arg506 is located at one of the APC cleavage sites of factor Va, the mutated factor Va is less sensitive to APC-mediated inactivation. 34 A single amino acid exchange causes factor V resistance to proteolysis by APC. 35 This mutation, which is thought to have an autosomal mode of inheritance,26 is the single most prevalent genetic defect associated with thrombosis
and may affect 3% to 7% of the general population. 36 Whereas the relative risk is increased 80-fold for homozygous persons, 37 it is increased sevenfold in heterozygous persons, 9 which is consistent with the history of recurrent thrombosis in our patient. However, in light of the high incidence of this mutation in the general population, factor V gene mutation alone does not fully account for this patient's problems. Additional predisposing factors include progressive deterioration of the venous system and microvascular occlusive disease related to smoking. Secondary lymphedema in this patient was most likely due to recurrent infections along with superficial and deep venous insufficiency. Conventional compression therapy may not be sufficient to prevent further progression of disease when high-degree venous insufficiency and extensive lymphedema are present. In these cases intermittent compression can be employed. This treatment, in combination with antibiotic treatment, debridements, and mesh grafting, proved to be effective in our patient.
REFERENCES
1. Coon WW. Venous thromboembolism.Prevalence,risk factors, and prevention.Clin Chest Med 1984;5:391-401. 2. SchaferAI. The hypercoagulablestates. Ann Intern Med 1985;102:814-28. 3. Egeberg O. InheritedantithrombinlII deficiencycausing thrombophilia. Thromb Diathes Haemorrh 1965;13:51630.
Journal of the American Academy of Dermatology Volume 35, Number 2, Part 2
4. Griffin JH, Evatt B, Zimmerman TS, et al. Deficiency of protein C in congenital thrombotic disease. J Clin Invest 1981;68:1370-3. 5. Schwarz HP, Fischer M, Hopmeier P, et al. Plasma protein S deficiency in familial thrombotic disease. Blood 1984;64: 1297-1300. 6. Bithell TC. Hereditary dysfibrinogenemia. Clin Chem 1985;31:509-16. 7. Aoki N, Moroi M, Sakata Y, et al. Abnormal plasminogen: a hereditary molecular abnormality found in a patient with recurrent thrombosis. J Clin Invest 1978;61:1186-95. 8. Allaart CF, Briet E. Familial venous thrombophilia. In: Bloom AL, Forbes CD, Thomas DP, et al. editors. Haemostasis and thrombosis. Edinburgh: Churchill Livingstone, 1994:1349-60. 9. DahlNick B, Carlsson M, Svensson PJ. Familial thrombophilia due to a previously unrecognized mechanism characterized by poor anticoagulant response to activated prorein C: prediction of a cofactor to activated protein C. Proc Natl Acad Sci U S A. 1993;90:1004-8. 10. DahlbBack B, Stenflo J. The protein C anlicoagulant system. In: Stamatoyannopoulos G, Nienhuis AW, Majems PW, et al. editors. The molecular basis of blood diseases. Philadelphia: WB Saunders, 1994:599-628. 11. Walker FJ. Regulation of activated protein C by a new protein: a possible function for bovine protein S. J Biol Chem 1980;255:5521-4. 12. Esmon CT. The roles of protein C and thrombomodulin in the regulation of blood coagulation. J Biol Chem 1989; 264:4743-6. 13. Esmon CT. Protein-C: biochemistry, physiology, and clinical implications. Blood 1983;62:1155-8. 14. van Hinsbergh VW, Bertina RM, van Wijngaarden A, et al. Activated protein C decreases plasminogen activatorinhibitor activity in endothelial cell-conditioned medium. Blood 1985;65:444-51. 15. DahlNick B, Stenflo J. The protein C anticoagulantsystem. In StamatoyannoponiosG, Nienhuis AW, Majerus PW, et al. editors. The molecular basis of blood diseases. Philadelphia: WB Saunders, 1994:599-628. 16. Hillarp A, Dahlb~ickB. Novel subunit in C4b-bindingprotein required for protein S binding. J Biol Chem 1988;263: 12759-64. 17. Dahlb~ick B. Inhibition of protein Ca cofactor function of human and bovine protein S by C4b-bindingprotein. J Biol Chem 1986;261:12022-7. 18. Comp PC, Nixon PR, Cooper MR, et al. Familial protein S deficiency is associated with recurrent thrombosis. J Clin Invest 1984;74:2082-8. 19. Bertina RM, Koeleman BP, Koster T, et al. Mutation in blood coagulation factor V associated with resistance to activated protein C. Nature 1994;369:64-7. 20. Thomas DP. Pathogenesis of venous thrombosis. In: Bloom AL, Forbes CD, Thomas DP, et al. editors. Haemostasis and thrombosis. Edinburgh: Churchill Livingstone, 1994:1335-47. 21. Coffman JD. Cutaneous changes in peripheral vascular
Peus et al.
22.
23.
24.
25. 26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
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disease. In: Fitzpatrick TB, Eisen AZ, Wolff K, et al. editors. Dermatology in general medicine. New York: McGraw-Hill, 1993:2077-104. McGhee WG, Klotz TA, Epstein DJ, et al. Coumarin skin necrosis associated with hereditary protein C deficiency. Ann Intern Med 1984;100:59-60. Perkins W, Downie I, Keefe M, et al. Cutaneous necrosis in pregnancy secondary to activated protein C resistance in hereditary angioedema. J R Soc Med 1995;88: 229P-30P. Tabemero MD, Tomas JF, Alberca I, et al. Incidence and clinical characteristics of hereditary disorders associated with venous thrombosis. Am J Hematol 1991;36:249-54. Miletich JP, Prescott SM, White R, et al. Inherited predisposition to thrombosis. Cell 1993;72:477-80. Svensson PJ, Dahlb~ick B. Resistance to activated protein C as a basis for venous thrombosis. N Engl J Med 1994; 330:517-22. Koster T, Rosendaal FR, de Ronde H, et al. Venous thrombosis due to poor anticoagulantresponse to activated protein C: Leiden thrombophilia study. Lancet 1993;342: 1503-6. Hellgren M, Svensson PJ, Dahlb~ickB. Resistance to activated protein C as a basis for venous thromboembolism associated with pregnancy and oral contraceptives. Am J Obstet Gynecol 1995;173:210-3. D'Angelo SV, Mazzola G, Della Valle P, et al. Variable interference of activated protein C resistance in the measurement of protein S activity by commercial assays. 1994;77:375-8. Faloni EM, Franchi F, Asti D, et al. Resistance to activated protein C in nine thrombophilic families: interference in a protein S fimctional assay. Thromb Haemost 1993;70:106771. Cooper PC, Hampton KK, Makris M, et al. Further evidence that activated protein C resistance can be misdiagnosed as inherited functional protein S deficiency. 1994;88:201-3. Voorberg J, Roelse J, Koopman R, et al. Association of idiopathic venous thromboembolism with single point-mutation at Arg506 of factor V. Lancet 1994;343:1535-6. Greengard JS, Sun X, Xu X, et al. Activated protein C resistance caused by Arg506Gln mutation in factor Va. Lancet 1994;343:1361-2. Ztller B, DahlNick B. Linkage between inherited resistance to activated protein C and factor V gene mutation in venous thrombosis. Lancet 1994;343:1536-8. Sun X, Evatt B, Griffin JH. Blood coagulation factor. Va abnormality associated with resistance to activated protein C in venous thrombophilia. Blood 1994;83:3120-5. Dahlb~ick B. Inherited thrombophilia: resistance to activated protein C as a pathogenic factor of venous thromboembolism. Blood 1995;85:607-14. Rosendaal FR, Koster T, Vandenbroucke JP, et al. High risk of thrombosis in patients homozygous for factor V Leiden (activated protein C resistance). Blood 1995;85: 1504-8.