Low heparin cofactor II associated with abnormal crossed immunoelectrophoresis pattern in two Norwegian families

Syndromes of Thrombosis and Hypercoagulability: Congenital and Acquired Thrombophilias

This article stresses the common hereditary and acquired blood protein defects associated with thrombosis. The most common of the hereditary defects apear to be APC-R, SPS, antithrombin, protein C, and protein S deficiency, and the most common acquired defects are anticardiolipin antibodies and the lupus anticoagulant (antiphospholipid antibodies). Therefore, these are the defects that should first be looked for in an individual with unexplained thrombosis. If these more common defects are not found, then the rarer defects including HC II, plasminogen or TPA deficiency, dysfibrinogenemia, el evated PAI-1 and hyperhomocysteinemia should be sought. The importance of finding these defects has significant impli cations for therapy of the individual patient and for institutions of family studies to identify, inform, and possibly treat others at risk. It is expected that as knowledge of hemostasis expands, more hereditary and acquired defects, such as elevated lipopro tein (a) or defects of extrinsic (tissue factor) pathway inhibitor (EPI, TFPI), may be associated with enhanced risks of throm bosis. Finally, it must be recalled that a diagnosis of thrombo sis, like that of anemia, is only a generic and partial diagnosis; just as in the anemic patient, the etiology must be clearly de fined. Only in this manner can cost-effective and appropriate therapy for both primary treatment and secondary prevention be designed. In addition, the demonstration of a hereditary defect will allow primary prevention in afflicted family mem bers by allowing the choice of appropriate therapy.

Inherited Thrombophilia

Inherited thrombophilia can be defined as a genetically determined predisposition to the development of thromboembolic complications. Since the discovery of activated protein C resistance in 1993, several additional disorders have been described and, at present, it is possible to identify an inherited predisposition in about 60 to 70% of patients with such complications. These inherited prothrombotic risk factors include qualitative or quantitative defects of coagulation factor inhibitors, increased levels or function of coagulation factors, defects of the fibrinolytic system, altered platelet function, and hyperhomocysteinemia. In this review, the main inherited prothrombotic risk factors are analyzed from epidemiological, laboratory, clinical, and therapeutic points of view. Finally, we discuss the synergism between genetic and acquired prothrombotic risk factors in particular conditions such as childhood and pregnancy.

Heparin cofactor II deficiency

OBJECTIVES

To review of the state of the art relating to congenital heparin cofactor II deficiency as a potential risk factor for thrombosis, as reflected by the medical literature and the consensus opinion of recognized experts in the field, and to make recommendations for the use of laboratory assays for assessing this thrombotic risk in individual patients.

DATA SOURCES

Review of the medical literature, primarily from the last 10 years.

DATA EXTRACTION AND SYNTHESIS

After an initial assessment of the literature, including review of clinical study design and laboratory methods, a draft manuscript was prepared and circulated to participants in the College of American Pathologists Conference XXXVI: Diagnostic Issues in Thrombophilia. Recommendations were accepted if a consensus of experts attending the conference was reached. The results of the discussion were used to revise the manuscript into its final form.

CONCLUSIONS

Consensus was reached that there is insufficient evidence to recommend testing for heparin cofactor II deficiency in patients with thromboembolic disease.

Syndromes of thrombosis and hypercoagulability. Congenital and acquired causes of thrombosis

Blood coagulation protein and platelet defects are now known to account for up to ninety percent of unexplained venous thrombosis and up to seventy percent of unexplained arterial thrombotic or ischemic events. This article summarizes the common and uncommon blood protein and platelet defects which should be suspected, and searched for, in patients with such events. Defining such defects will have major impact on secondary prevention and duration of antithrombotic therapy in the afflicted patient and impact on primary prevention for identified family members in those harboring hereditary defects.

Hematologic disorders associated with ischemic stroke

Hematological disorders underlie a small proportion of all ischemic strokes. The association of these coagulation abnormalities with ischemic stroke is not always clear. The etiology of stroke still remains uncertain in a large number of cases and proper screening for coagulation abnormalities and the discovery of new coagulation disorders will probably increase the rate of strokes attributable to these causes. Since large case-control studies with unselected and consecutive stroke patients from different ethnic origins have not yet been performed to determine the role of coagulation abnormalities in ischemic stroke, our knowledge is dependent on case reports and small series of mostly younger patients. Extensive hematologic evaluation of unselected stroke patients will likely yield little useful information and be too expensive. Every stroke patients needs a careful evaluation, and in selected cases, this should include coagulation parameters. Patients with unexplained strokes after a careful evaluation, previous thrombotic episodes, or a positive family history for thrombosis, are good candidates for further coagulation studies. As long as the hypercoagulable state persists, both arterial and venous thromboembolic recurrences can be expected. Many of these patients may benefit from anticoagulants. In patients with hereditary coagulation disorders, studies should be extended to close relatives. Since some coagulation tests are fairly expensive, provide only equivocal data, and are not widely available, we advise a step-by-step approach starting with the patient and family history.

The molecular genetics of familial venous thrombosis

This study of naturally occurring mutations predisposing to venous thrombosis has led to a number of important advances in our understanding of protein structure and function relationships and the molecular basis of gene mutation. It has also potentiated the accurate and reliable presymptomatic and antenatal detection of predisposing gene lesions. Perhaps the major challenge facing us is the probabilistic nature of thromboembolism; only a certain proportion of patients with recognized gene defects predisposing to thrombosis will actually suffer from thrombotic episodes. Environmental insults of various kinds, and perhaps epistatic effects resulting from the influence of other loci, are likely to be contributory factors and will help to determine whether a thrombotic event occurs in individuals already compromised by a defect in a gene whose malfunction is known to predispose to thrombosis. Since molecular genetic techniques allow us to dissect the allelioheterogeneity of the different deficiency states by characterizing the wide spectrum of gene mutations giving rise to thrombosis, it may eventually prove possible to relate specific gene lesions to the probability of thromboembolism as well as to the severity and frequency of thrombotic episodes. The multifactorial nature of thrombosis demands a multidisciplinary approach to the analysis of its causation, early detection, treatment and prevention. The application of the new and powerful techniques of molecular genetics promises to make a substantial contribution to all aspects of thrombosis research.

Hypercoagulability and thrombosis

This article has stressed the common hereditary and acquired blood protein defects associated with thrombosis. The commonest hereditary defects appear to be antithrombin, protein C, and protein S deficiency, and the commonest acquired defects are anticardiolipin antibodies and the lupus anticoagulant. Therefore these are the defects that should first be looked for in an individual with unexplained thrombosis. If these commoner defects are not found, the rarer defects, including HC-II, plasminogen or t-PA deficiency, dysfibrinogenemia, or elevated PAI-1, should next be sought. The incidence of activated protein C cofactor deficiency is not yet clear but may also represent a common defect. Likewise, PAI-1 defects may, with time, be shown to be quite common. The importance of finding these defects has significant implications for therapy of the individual patient and for institution of family studies to identify, inform, and possibly treat others at risk. It is expected that as knowledge of hemostasis expands, more hereditary and acquired defects, such as elevated lipoprotein (a) or defects of extrinsic (tissue factor) pathway inhibitor may be associated with enhanced risks of thrombosis.

The interaction of glycosaminoglycans with heparin cofactor II

The binding sites for dermatan sulfate and heparin in HCII overlap but are not identical. This may explain the observation that HCII binds nonspecifically to heparin oligosaccharides, but preferentially binds to a minor hexasaccharide isolated from dermatan sulfate. The tissue distribution of dermatan sulfate molecules containing the high-affinity HCII binding site may regulate HCII activity in vivo. Finally, in the presence of dermatan sulfate or heparin, the N-terminal acidic region of HCII may interact with the hirudin-binding site of thrombin to produce maximal stimulation of the thrombin-HCII reaction.

Glycosaminoglycans and the regulation of blood coagulation

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Hereditary heparin cofactor II deficiency and coronary artery disease

We here present a Japanese family with type I hereditary heparin cofactor II (HC II) deficiency. The propositus (a 61-year-old man) suffered from angina pectoris and coronary artery disease was confirmed by coronary angiography. He underwent percutaneous transluminal coronary angioplasty (PTCA) four times in one year. Combined use of heparin, aspirin, and nitrates could not prevent the return of his symptoms and restenosis of segment 6 of the left anterior descending artery. His HC II activity and antigen levels were 49% and 50%, respectively, and his daughter also showed similar low levels. Cerebral infarction had occurred in two family members. Argatroban, a selective potent thrombin inhibitor, was administered after the fourth PTCA for the purpose of preventing reocclusion and achieved a successful outcome. A relationship between HC II deficiency and thrombosis has not yet been established. Our case suggests that standard heparin therapy is not effective in preventing restenosis in such individuals, in whom the process is accelerated by thrombin generation at the site where PTCA produces rupture of the atherosclerotic plaque. Argatroban may be more effective under low HC II conditions because of its potent inhibition of thrombin activity at sites of vascular wall damage.

An enzyme-linked immunosorbent assay for heparin cofactor II (HCII). Application to the measurement of HCII in clinical materials

Heparin cofactor II (HCII) is a thrombin inhibitor in human plasma, the activity of which is enhanced by heparin and dermatan sulfate. To measure the plasma antigen concentration of HCII, an enzyme-linked immunosorbent assay (ELISA) has been developed, and this is based on the use of polyclonal anti-HCII IgG, both as the antigen-capturing antibody and as the labelled antibody. The intra- and inter-assay reproducibilities have been calculated to be less than 6%. HCII antigen concentrations evaluated with this ELISA technique in clinical plasma samples correlated well with those determined by electroimmunodiffusion and with HCII activities evaluated using a functional assay (r = 0.909 and r = 0.930, P less than 0.0001). Since the correlation between HCII deficiency and thrombosis is still a controversial issue, the ELISA technique described in this report could be a useful tool for the large-scale studies needed to determine the prevalence of HCII deficiency in healthy individuals and in patients with a history of thrombosis.

The interaction of glycosaminoglycans with heparin cofactor II: structure and activity of a high-affinity dermatan sulfate hexasaccharide

The binding sites for dermatan sulfate and heparin in HCII overlap but are not identical. This may explain the observation that HCII binds non-specifically to heparin oligosaccharides but preferentially binds to a minor hexasaccharide isolated from dermatan sulfate having the structure shown in Fig. 4B. The tissue distribution of dermatan sulfate molecules containing the high-affinity HCII binding site may regulate HCII activity in vivo. Finally, in the presence of dermatan sulfate or heparin, the N-terminal acidic domain of HCII may interact with the hirudin-binding site of thrombin to produce maximal stimulation of the thrombin-HCII reaction.

The molecular genetics of familial venous thrombosis

Inherited defects of antithrombin III, protein C, protein S, heparin cofactor II, plasminogen and the fibrinogens are thought to be responsible for between 10 and 15% of all patients presenting with recurrent venous thrombosis. The structure, function and expression of these genes and the nature of the gene lesions underlying the deficiency states are reviewed in detail.

Screening for inherited thrombotic disorders

In order to determine a scheme for the screening of inherited thrombotic disorders, abnormalities considered as predisposing to thrombosis have been reviewed. Owing to the low prevalence of biological alterations, a selection of patients is required: documented venous thromboses, possibly at unusual sites (mesenteric vein, portal, cerebral veins), occurring before the age of 40 in patients with a positive family history of thromboses are relatively frequently associated with coagulation abnormalities. In addition, patients with skin necrosis at the initiation of oral anticoagulants, or with repeated superficial vein thrombosis or unexplained arterial occlusions at a young age might be included for screening. Tests have also to be selected. Some abnormalities, such as congenital deficiencies in antithrombin III, protein C and protein S, are recognized risk factors and have to be searched. Some others cannot be at present considered as definite risk factors (e.g., dysfibrinogenemias or deficiencies in factor XII), but their detection is easy by routine tests: prothrombin time, fibrinogen assay. Other abnormalities are recognized risk factors (or not) and need specific uncommon tests (e.g., study of fibrinolysis). Each time a biological abnormality is found, it is important to verify it is isolated since combined deficiencies have been observed and we should be able to answer the question whether the abnormality is the cause or the consequence of thrombosis, or a coincidence. Finally, in our experience, even in well selected patients, a coagulation disorder is detected in less than 30% of patients, so that new tests are needed to improve our knowledge in this field.

Heparin cofactor II in adults and infants with thrombosis and DIC

Heparin cofactor II (HC II) was measured by a chromogenic activity assay in normal preterm infants (gestational age, 28-36 weeks; n = 17; 29% +/- 11.5 [mean +/- 1 SD], range 11-51), normal full-term infants (n = 18; 49% +/- 6.6 [mean +/- 1 SD], range 36-58), and normal adults (n = 38; 101% +/- 14 [mean +/- 1 SD], range 73-130). Normal children attained adult levels at approximately 5 to 7 months of age. The lower values in preterm and term infants most likely reflect immature liver function. Neither adults and children with a history of thrombosis with prior negative evaluation (n = 74), patients with documented protein C and protein S deficiency (n = 4), nor sick infants without evidence of consumptive coagulopathy (n = 15) had significantly lower levels of HC II activity. Infants with disseminated intravascular coagulation (n = 2) had strikingly lower levels of HC II activity.

Studies on the structural requirements of heparin for the catalysis of thrombin inhibition by heparin cofactor II

The structural requirements of heparin for the catalysis of thrombin inhibition by heparin cofactor II (HC II) were investigated. A series of well characterized heparin derivatives were prepared and their activities were measured using human thrombin in the presence of an excess of purified human HC II and, for comparison, antithrombin III (AT III). The 50% inhibitory concentrations of each derivative were calculated and compared with those of unmodified heparin. Heparin activity was strongly dependent on molecular weight (Mr) in a manner grossly comparable for the two inhibitors. High-Mr fractions were the most active. Below 10 kDa, the activity dropped rapidly. A minimum size of 26 residues appeared to be required for HC II activation (against 16-18 for AT III). Below 5 kDa, a residual activity two orders of magnitude lower than that of high-Mr species remained with HC II (but not with AT III). Heparin was selectively desulfated or oversulfated in the O- and/or N-position. When an N-acetyl group was substituted for the original N-sulfate in the glucosamine and the derivative was oversulfated in the O-position, a strong activity with HC activities with both inhibitors decreased when the overall sulfate content (i.e., the charge density) was reduced, and vice-versa. Carboxyl-reduced heparin was also inactive but activity could be restored after O-sulfation. Our results thus suggest that, unlike the case of AT III, no functional group in heparin is critical for optimal thrombin inhibition by HC II. Sulfate and carboxylate are important in as much as they contribute to the global charge of the molecule.