Congenital bleeding disorders of the vitamin K-dependent clotting factors.

ABSTRACT

Congenital bleeding disorders of the vitamin K-dependent coagulation factors represent only about 15-20% of all congenital bleeding disorders. However, they played an important role of the history of blood coagulation. Prothrombin was the first entity dealt with. Subsequently, in the late 1940s or early 1950s, the discovery of factor IX allowed the separation of hemophilia into two groups, A and B. In the 1950s, the discovery of factors VII and X allowed the formulation of a logic and plausible explanation for the clotting mechanism. The subsequent discovery of vitamin K-dependent proteins with an inhibitory effect on blood coagulation has further enhanced the importance of the vitamin K-dependent clotting factors. Recently, the study of families with multiple defects of the prothrombin complex has spurred the interest in vitamin K metabolism and the gamma-carboxylation system. The relevance of these studies had also an important role in the understanding the mechanism of action of other noncoagulation-related proteins. The vitamin K-dependent clotting factors represent a homeostatic mechanism at the basis of the hypercoagulability (thrombosis)-hypocoagulability (hemorrhagic) system, namely, to a mechanism that is vital for survival. The different bleeding condition will be dealt with separately, namely, prothrombin or Factor II, Factor VII, Factor IX (hemophilia B), and Factor X deficiencies. An additional heading deals with the combined defect of the prothrombin complex, namely, combined deficiency of Factor II, Factor VII, Factor IX, and Factor X. Since, sometimes, a hemorrhagic role has been attributed to Protein Z deficiency, another vitamin K-dependent protein, this defect will also be dealt with, even though briefly. Each deficiency has been approached in a global manner, namely, with adequate reference to history, background, prevalence, classification, hereditary pattern, biochemistry and function, molecular biology, clinical picture, updated laboratory diagnosis, prognosis, and therapy. Particular emphasis has been placed on the significance of cases with "true" deficiency [cross-reacting material (CRM negative)] and cases with abnormalities (CRM positive). The genetic, clinical, and laboratory implications of these two forms have been extensively discussed in every instance. The importance of a multiple, combined diagnostic approach that has to include whenever possible clotting, chromogenic, immunological, and molecular biology studies has been underlined. Clotting tests have to be carried out using different activating agents since results may vary, thereby indicating a different reactivity of the abnormal protein. Molecular biology techniques, alone, are unable to supply plausible diagnostic conclusions. In fact the genotype-phenotype relation has not been clarified so far for most of these bleeding conditions. Recent progress in management such as the use of recombinant factor concentrates, results of liver transplantation, and attempts at genetic therapy has been discussed. Potential complications of therapeutic measures have also been discussed. A section dealing with future putative aims of research in this field will close the chapter.