Chapter 472 Hereditary Predisposition to Thrombosis
Pediatricians are frequently asked to evaluate children for inherited risk factors for thrombosis with symptomatic thrombosis or asymptomatic children who have relatives affected with either thrombosis or thrombophilia. The clinical utility of thrombophilia testing is debated, both in adults and children.
Thrombophilia testing rarely influences the acute management of a child with a thrombotic event. The association between inherited thrombophilia and pediatric thrombosis varies based on the clinical scenario: children with unprovoked thrombotic events have a high prevalence of inherited defects, while the role of thrombophilic defects in children with catheter-related thrombotic events is questionable. Although some thrombophilic defects are associated with a higher risk of recurrent venous thromboembolism in children, how to use these results to guide the duration of therapy has not been determined. Prospective longitudinal analyses of such patients to determine outcome and response to treatment as well as the impact of known thrombophilic states on these outcomes are clearly needed.
The decision to perform thrombophilia testing in an otherwise healthy child with a family history of thrombosis or thrombophilia should be carefully considered, weighing the potential advantages and limitations of such an approach. Given that the absolute risk of thrombosis in children is extremely low (0.07/100,000), it is unlikely that an inherited thrombophilia will have any impact on clinical decision-making for a young child. The risk of thrombosis increases with age, so that identification of a thrombophilic defect in an adolescent may guide thromboprophylaxis in high-risk situations (lower extremity casting or prolonged immobility), inform the discussion about estrogen-based contraceptives, and may promote lifestyle modification to avoid behavioral prothrombotic risk factors (sedentary lifestyle, dehydration, obesity, and smoking). Limitations of such testing include the cost as well as the potential for causing unnecessary anxiety or false reassurance.
The most common inherited thrombophilias are listed in Table 472-1 . The inherited defects in which the pathogenic link is best understood include the factor V Leiden mutation, the prothrombin gene mutation, and deficiencies of protein C, protein S, and antithrombin (AT). Elevated levels of factor VIII, lipoprotein (a), and homocysteine are associated with thrombosis, though these are less well characterized and not necessarily genetically determined. Although there are additional alterations in coagulation that have been associated with thrombotic risk, including elevated concentrations of factors IX and XI, heparin cofactor II deficiency, and dysfibrinogenemia, none has gained widespread acceptance in routine testing of children for inherited thrombophilia.
Table 472-1 INHERITED THROMBOTIC DISORDERS
CLASSIFICATION AND DISORDERS INHERITANCE CLINICAL FEATURES DEFICIENCY OR QUALITATIVE ABNORMALITIES OF INHIBITORS OF ACTIVATED COAGULATION FACTORS AT deficiency AD Venous thromboembolism (usual and unusual sites), heparin resistance TM deficiency AD Venous thromboembolism Protein C deficiency AD Venous thromboembolism Protein S deficiency AD Venous and arterial thromboembolism APC resistance AD Venous and arterial thromboembolism IMPAIRED CLOT LYSIS Dysfibrinogenemia AD More venous thrombosis than arterial thrombosis Plasminogen deficiency AD, AR Venous thromboembolism TPA deficiency
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