A novel congenital haemostatic defect

&NA; Isolated deficiencies of factors VII and XI are both rare. Not surprisingly, therefore, combined factor VII and XI deficiency has not been reported previously. We report here a kindred with a combined heterozygous deficiency for both factors VII and XI. The proposita is a 28-year-old woman who had both a prolonged prothrombin time (PT) and a prolonged activated partial prothrombin time (APTT) associated with a mild bleeding tendency. Coagulation studies were performed on the six available members of this kindred. The PT and APTT were normal or mildly abnormal in five of these individuals. Factor VII coagulant activity (VII:C) varied from 0.33 to 0.77 units/ml in affected subjects. In contrast, the concentration of factor VII-related antigen for the six individuals ranged from 0.68 to 2.10 units/ml. Comparable factor VII:C levels were obtained when each subject's plasma was tested with either a rabbit or a human thromboplastin reagent. Factor XI coagulant activity was less than 0.5 units/ml in three of the six subjects and normal (˜ 1.0 units/ml) in the other three. The concentrations of thrombin-antithrombin-III and prothrombin fragment 1.2 were within normal limits for all individuals. In addition to being associated with heterozygous factor XI deficiency, the abnormalfactor VII molecule in the plasma of affected individuals in this kindred appears to represent a newly described mutation. This is suggested by the pattern of reactivity with thromboplastin from different species, the normal tissue factor binding and the bleeding tendency in heterozygous individuals in this kindred.