Multicentre evaluation of combined prothrombotic defects associated with thrombophilia in childhood

To evaluate the role of multiple established and potential causes of childhood thrombophilia, 285 children with a history of thrombosis aged neonate to 18 years (first thrombotic onset) were investigated and compared with 185 healthy peers. APC- resistance (FV:Q506), protein C, protein S, antithrombin, heparin cofactor II (HCII), histidine-rich glycoprotein (HRGP), and prothrombin (F.II), factor XII (F.XII), plasminogen, homocysteine and lipoprotein (a) (Lp(a)) were investigated. In 59% of patients investigated one thrombotic defect was diagnosed, 19.6% showed two thrombotic risk factors, while in 21.4% of children investigated no risk factor could be identified. Single defects comprised established causes of inherited thrombophilia: FV:Q506 (homozygous n = 10, heterozygous n = 69), protein C (homozygous n = 1; heterozygous n = 31), heterozygous type I deficiency states of protein S (n = 7), antithrombin (n = 7) and homocystinuria (n = 6); potentially inherited clotting abnormalities which may be associated with thrombophilia: F.XII (n = 3), plasminogen (n = 2), HCII (n = 1), increased HRGP (n = 4); new candidate risk factors for thrombophilia: elevated plasma levels of Lp(a) (n = 26), F.II (n = 1). Heterozygous FV:Q506 was found in combination with heterozygous type I deficiency states of protein C (n = 2), protein S (n = 13), antithrombin (n = 8) and HCII (n = 1), increased Lp(a) (n = 13), and once each with elevated levels of F.II, moderate hyperhomocysteinemia, fibrinogen concentrations >700 mg/dl and increased HRGP. In addition to the association with FV:Q506, heterozygous protein C type I deficiency was combined with deficiencies of protein S (n = 2), antithrombin (n = 1), and increased Lp(a) (n = 3). One patient showed protein C deficiency along with familially increased von Willebrand factor >250%. Besides coexistence with FV:Q506 and protein C deficiency, protein S deficiency was combined with decreased F.XII and increased Lp(a) in one subject each. Furthermore, we found combinations of antithrombin deficiency/elevated Lp(a), hyperhomocysteinemia/Lp(a), deficiency of HCII/plasminogen, and plasminogen deficiency along with increased Lp(a) each in one. Increased prothrombin levels were associated with fibrinogen concentrations >700 mg/dl and with HCII deficiency in one child each. Carrier frequencies of single and combined defects were significantly higher in patients compared with the controls.