Heterozygous FXII deficiency is not associated with an increased incidence of thrombotic events: Results of a long term study

OBJECTIVE: To investigate the incidence of thrombotic events in patients heterozygous for FXII deficiency during a long observation period. PATIENTS AND METHODS: 103 heterozygotes for FXII deficiency, 49 female and 54 male were followed for 19.6 years (range 5-32 years). As controls 103 unaffected family members of same sex and similar age (±5 years) were enrolled. The thrombotic end points were: myocardial infarction, deep vein thrombosis and ischemic stroke. The mean Factor XII level in the heterozygotes was 48.5%: range (35-60%) that of control was 96.5% (range 70-155%). The heterozygotes showed one myocardial infarction, two deep vein thromboses and no ischemic stroke. The unaffected family members observed 2 myocardial infarctions, one deep vein thrombosis and one ischemic stroke. There were seven deliveries (five women) among the heterozygotes and six (five women) among the controls. Furthermore, four and five surgical procedures were carried out in the patient and in the control group, respectively. Immobilization times for surgical procedures or pregnancies were 50 days and 57 days for the heterozygotes and the unaffected family members, respectively. Heterozygotes for FXII deficiency did not show an increased incidence of thrombotic events as compared with unaffected family members during a long follow up.