Reevaluation of the incidence of thromboembolic complications in congenital factor XII deficiency - A study on 73 subjects from 14 Swiss families

To further elucidate the debated role of hereditary FXII deficiency as a th rombophilic risk factor this follow-up study on 65 subjects out of 12 Swiss families was undertaken (follow-up: 6 yrs). Fifteen severely FXII deficien t subjects (FXII:C <1%), 35 partially FXII deficient subjects (FXII:C great er than or equal to 1-59%), 10 with normal FXII values (FXII:C greater than or equal to 70%), and 5 non-classifiable subjects (FXII:C greater than or equal to 60-69%) were reevaluated. Eight subjects (4 severely and 3 partial ly FXII deficient, 1 non-classifiable) were newly enrolled. Four instances of deep vein thrombosis, one superficial vein thrombosis and one myocardial infarction were noted in 2 our of 19 severely FXII deficient subjects duri ng a total life-time period of 866.6 patient-years. In 38 partially FXII de ficient subjects (1862.8 patient-years) one ischemic cerebrovascular stroke and one superficial vein thrombosis were recorded in 2 individuals. The 10 subjects with normal FXII values (498.2 patient-years) remained thrombosis -free. One superficial vein thrombosis occurred in an unclassifiable woman. None of the 3 different FXII gene defects revealed in our patients was spe cifically associated with thromboembolic complications. Kaplan-Meier analys is of thrombosis-free survival suggests that hereditary partial (and probab ly severe) FXII deficiency does not constitute a thrombophilic condition.