Fibrinolytic studies in 13 unrelated families with factor XII deficiency.

Background And Methods: We report the results of extensive "in vitro" fibrinolytic studies in 18 homozygous and 14 obligatory heterozygous subjects belonging to 13 unrelated families with factor XII deficiency. All homozygotes had unmeasurable factor XII activity (XII:C) and antigen (XII:Ag). None had bleeding symptoms, whereas a myocardial infarction occurred in one of them at age 51.