Laboratory and clinical aspects of inherited thrombotic disorders

Hypercoagulable State

BACKGROUND

The hypercoagulable state results from a complex interplay of blood coagulation factors, coagulation-inhibitory factors, platelets and the vascular endothelium. Imbalance of the complex interplay between these factors results in thrombosis often complicated by embolism. The causes of thrombosis are varied and maybe congenital or acquired. The current interest is centered on the congenital deficiency of coagulation inhibitors as there is an increasing awareness of their involvement in thrombosis, especially in the young.

METHODS

A total of 42 patients with thrombosis were studied. The most common clinical presentation was deep vein thrombosis. All the cases were evaluated for coagulation inhibitors Antithrombin, resistance to activated protein C, Protein C and Protein S using standard assay kits.

RESULTS

Resistance to activated protein C (n=10) was seen to be the commonest cause of thrombophilia. This was followed by deficiency of Antithrombin (n-4), Protein C (n=3) and Protein S (n=2). Majority of our cases were in the third decade of life.

CONCLUSION

The identification of the underlying aetiology is important for instituting specific therapy and patient management.

Inherited thrombotic disorders: an update

Significant advances in identification of etiologies of inherited thrombosis have been recently reported. A point mutation in coagulation factor V (factor V Leiden) results in resistance to activated protein C and probably represents the most common genetic risk factor for venous thrombosis. A metabolic disorder, homocysteinemia, is now known to be an important risk factor for both arterial and venous thrombosis. Many patients with recurrent thrombosis will have more than one genetic risk factor identified. Recognition of these new disorders should permit a diagnosis to be achieved in at least half of patients evaluated for inherited thrombosis.

Evidence against hypercoagulability in coronary artery disease

The strong epidemiological association between elevated plasma clotting factors and coronary artery disease is generally interpreted as evidence that patients with coronary atherosclerosis are in a procoagulant (hypercoagulable) state. A dynamic global test was used to assess the overall coagulation status of 761 patients with coronary artery disease scheduled for coronary artery bypass grafting and compared to healthy matched controls (n = 100). Platelet reactivity to shear-stress was simultaneously measured from identical, non-anticoagulated blood samples. Contrary to expectation, the overall coagulation in cardiac patients did not differ significantly from that of controls. Furthermore, the coagulation status of patients bore no relationship to the severity of coronary atherosclerosis. The latter is in contrast with platelet reactivities, which were significantly increased in patients with > or = 2 vessel disease as compared with single vessel disease. The present results do not necessarily conflict with the finding of elevated plasma clotting factors in cardiac patients. However, they do not support the claim that these markers are a reflection of a hypercoagulable state. Indeed, this study confirms that such patients are in a prothrombotic state, which is related to enhanced platelet reactivities, and not to a prothrombotic imbalance of the coagulation mechanism.

Extracardiac thrombotic, embolic, and hemorrhagic causes of sudden death

The integrity of the vascular tree is essential to sustain life. However, blood vessels are the most vulnerable structure in the cardiovascular system, and disruption of the vasculature by occlusion (thrombosis/thromboembolism) or leakage (hemorrhage) can lead to sudden death. This review will concentrate on the extracardiac manifestations of two opposite, but intimately related, pathophysiologic processes that disturb vascular integrity: namely, thrombosis and hemorrhage. Thrombosis is a pathological process that leads to activation of the hemostatic system at an abnormal time and location. We are only just beginning to appreciate the myriad causes of thrombosis, some of which include vascular factors such as stasis and endothelial injury, as well as blood factors such as excessive coagulation, decreased coagulation inhibitors, or decreased fibrinolysis. Hemorrhage is a frequent cause of sudden death and may be attributable to blood vessel disease/rupture or to abnormalities within the blood itself that impair hemostasis. In this review, the pathophysiologic mechanisms of thrombosis/thromboembolism and hemorrhage are delineated and multiple system-specific disease entities are discussed.

Ischemic stroke in the young: evaluation and age comparison of patients six months to thirty-nine years

Ischemic stroke in the young is uncommon, but we currently evaluate at least one young stroke patient at our institutions each week. We undertook this chart review of strokes in patients between the ages of 6 months and 39 years to review all conditions associated with, and thus possibly contributory to, the stroke. We also compare younger and older age groups to observe if age-dependent factors exist. Of 100 total ischemic strokes, 22 were in persons 6 months to 18 years and 78 were in persons 19 to 39 years. Seventy-five percent of strokes were associated with a condition known or postulated to increase stroke risk. Some of these conditions are well accepted as causes for stroke, such as some forms of heart disease, whereas others are only postulated, such as the hypercoagulable states. Taken as a whole, associated conditions were approximately equally divided between infectious/inflammatory, structural, and presumed hypercoagulable conditions. Strokes in the first two decades of life were more commonly associated with infectious/inflammatory conditions, whereas strokes in the next two decades more commonly had structural or presumed hypercoagulable associated conditions. Since many strokes remain unexplained, it would be valuable to determine the significance, if any, of conditions less well known as risk factors for stroke.