An isolated deficiency of factor X is known to occur in a hereditary form, the Stuart-Prower disease, and in an acquired form in some patients with para-proteinaemia and sporadically in systemic amyloidosis. Transient deficiency of factor X in the presence of normal levels of factors II, VII and V appears to be rare. In the literature, only three cases have been described. We have studied a patient with a severe haemorrhagic diathesis and concomitant mycoplasma pneumonial infection. The bleeding tendency proved to be due to isolated factor X deficiency. No circulating inhibitors of factor X were present. Systemic amyloidosis could not be demonstrated. Factor X-related antigen could not be detected (this test was kindly performed by Dr.Daryl S.Fair, Scripps Clinic and Research Foundation, La Jolla, U.S.A.). Treatment with vitamin K, prothrombin complex concentrate, fresh plasma and whole blood proved not to influence factor X activity in the patient’s plasma. However, 20 days after admission⋅to hospital both factor X activity and antigen spontaneously returned to normal. These results suggest that the synthesis of factor X was transiently defective. Since other conditions known to affect factor X activity could not be demonstrated, it is postulated that the acquired factor X deficiency in this patient was related to the infection with mycoplasma pneumoniae.
