Congenital factor X deficiency in Japan.

Congenital factor X deficiency is a very rare inherited coagulation abnormality. There have been reported 43 cases of this disorder in the world and only 2 cases in Japan. Recently, we have hemostatically and immunologically examined as many as 3 cases of this rare disease, 18-year-old male, 11-year-old male and 6-year-old female. Hemostatic examinations revealed prolonged prothrombin time, partial thromboplastin time and decreased serum thromboplastic activity in these 3 cases. Stypven-cephalin clotting time was also abnormal. Factor X activities of our cases were low when assayed by either tissue thromboplastin and partial thromboplastin or by Stypven-cephalin mixture, which were 2.6, 1.5 and 4.5%, respectively. The half lives of infused factor X were 24, 38.6 and 56 hr, respectively, which are consistent with the data of other authors. Immunological assay of factor X (radioimmunoassay) showed 0.47 microgram/ml in the second case and 0.15 microgram/ml in the third case, from which our cases were considered to be classical factor X deficiency.