Factor X Friuli Coagulation Disorder: Almost 50 Years Later.

The story of factor X (FX) Friuli. Factor X Friuli was discovered in 1969 to 1970. However, the story of that disease was an international event since patients with this defect were studied in France and in Italy, and different diagnoses were reached-FVII; FX; combined prothrombin complex; and combined FII, FVII, and FX deficiencies. The diagnostic difficulties were due to the peculiar clotting pattern presented by these patients, namely, prolonged partial thromboplastin time, prolonged prothrombin time but normal Russell viper venom clotting time. Only suitable anti-FX antisera clarified the pattern. Altogether 12 homozygotes and 102 heterozygotes have been followed during 4 decades. Six homozygotes died, 2 of them due to HIV infection and 1 due to hepatitis B liver cirrhosis. The other 3 died of nontransfusion-related morbidity. Bleeding tendency has been moderate in agreement with the extrinsic or intrinsic system assay results-FX level of 4% to 5% is considered normal. Heterozygotes may present occasional bleeding manifestations usually during surgery or delivery. Molecular analysis have shown that the mutation responsible for the defect is a Pro343Ser substitution in exon 8. Chimeric FX Friuli mice have been useful in studying the effect of FX levels on embryonic or natal mortality of these animals. No new homozygote but several heterozygotes have been recently seen. The study of FX Friuli has revolutionized the diagnostic approach to FX deficiencies. The FX should be assayed by all assay systems. The FX Friuli has never been described in any other country, and all patients studied come from the Friuli Meduna River Valley.

Prevalence of bleeding manifestations in 128 heterozygotes for Factor X deficiency, mainly for FX Friuli, matched versus 128 unaffected family members, during a long sequential observation period (23.5 years).

OBJECTIVES: The main objective of the study was to evaluate the incidence of bleeding manifestations in heterozygotes for FX deficiency vs. unaffected family members. Secondary objective was to compare the prevalence of arterial or venous diseases found in the two groups. PATIENTS AND METHODS: A total of 128 heterozygote patients for FX deficiency were investigated. A total of 102 patients had FX Friuli; 26 patients had other forms of FX deficiency. At time of diagnosis, each patient was paired with an unaffected family member, matched by gender and age (±5). Patients and their normal counterparts were checked every 1-2 yr for a mean period of 23.5 yr. The occurrence of bleeding manifestations was recorded and scored. The occurrence of arterial diseases and venous thrombosis was also recorded as a secondary finding. RESULTS: A total of 38 heterozygote patients (29.7%) had one or more than one bleeding manifestation. The most frequent one was bleeding after tooth extraction or surgery. On the contrary, only three control subjects (2.3%) had documented hemorrhagic symptoms. There was a good correlation between bleeding and FX levels. Arterial disease (acute coronary syndromes, ischemic stroke, stable angina, peripheral arteries disease) was found in eight patients (6.3%) with FX deficiency and in seven unaffected subjects (5.5%). On the contrary, no venous thrombosis was seen in the affected group, whereas three cases (2.3%) of documented venous thrombosis were observed in the control group (two deep veins and one superficial vein). CONCLUSIONS: Heterozygotes FX deficiency may be accompanied by a mild bleeding tendency. This has important implications to assure a safe FX level in case of surgery or invasive procedures. Furthermore, mild FX deficiency seems to have no protective effect on arterial disease but does seem to protect from venous thrombosis.

Complex history of the discovery and characterization of congenital factor X deficiency.

Factor X (FX) plays a pivotal role in blood coagulation. FX represents the point where all coagulation systems converge and, once activated, it converts prothrombin into thrombin. The discovery and definition of FX are based on the description between 1956 and 1957 about three patients and their families with a peculiar defect later demonstrated to be almost identical. These patients were an American (Mr. Stuart), a British (Ms. Prower), and a Swiss with Italian background (infant Delia B). We stated "almost identical" because immunological and molecular biology studies subsequently revealed that even though the basic clotting defect was identical, the FX protein level and the mutation were different in each case. Mr. Stuart had no FX protein in his plasma and the mutation was Val298Met (homozygote). Ms. Prower instead had a normal level of FX protein and the mutation was Arg287Trp + Asp282Asn (compound heterozygote). Unfortunately, the status of the Swiss patient in this regard is not known. Subsequent studies described a few major variants (FX Friuli, FX Melbourne, FX Padua, and other similar patients), which showed peculiar activation patterns (FX Friuli had a normal Russell viper venom clotting time; FX Melbourne was defective only in the intrinsic coagulation system; FX Padua, on the contrary, was defective only in the extrinsic coagulation system). All these studies have informed on the great heterogeneity and complexity of the FX defect. The story of the discovery and classification of FX deficiency has contributed considerably to our understanding of blood coagulation. The three original families and the families of the major variants, together with the researchers that discovered them, should be remembered with deep respect and gratitude.