The Enigma of Severe Factor XI Deficiency without Hemorrhagic Symptoms

Summary A case of very severe P. T. A. deficiency without hemorrhagic symptoms is described, and the possibility that the absence of a bleeding diathesis may have an explanation in the presently unknown interrelationship between 3 “contact phase” coagulation factors is suggested. The existence of “Fletcher factor” deficiency as an entity distinct from factor XI and XII deficiency is confirmed. The problems in establishing a diagnosis of P. T. A. deficiency are discussed. The authors believe that assay using known congenitally deficient plasma is the only certain method of diagnosing P. T. A. deficiency. The 3 members of the propositus’s family have minor P. T. A. deficiency, and the mode of inheritance in this family is consistent with the hypothesis of Rapaport et al.