Twelve patients with an acquired inhibitor of Factor V have been reported thus far in the literature. Of these, only one occurred in a patient with hereditary Factor V deficiency. Six patients received streptomycin in close temporal relationship to the appearance of the inhibitor. Six of the patients had been previously transfused, including four of those who received streptomycin. In nine of the eleven spontaneously occurring inhibitors, major surgery preceded the appearance of the inhibitor. The degree of clinical bleeding in these patients varied. One patient had no bleeding, six patients had mild to moderate bleeding, and four patients had severe bleeding. The inhibitor disappeared in less than eight weeks in seven patients, whereas in one patient it persisted for more than two years. Most of these inhibitors have the physiochemical properties of antibodies. Six of the spontaneous inhibitors appeared to be IgG, whereas in two patients inhibitor activity was found in both IgM and IgG fractions. Three inhibitors have been typed with light chain antisera and all contained both kappa and lambda chains. Plasmas from seven patients with hereditary Factor V deficiency have been tested with three of these inhibitors for inactive factor V antigenic material and none has been detected. In addition, plasma from a patient with hereditary factor V deficiency has been tested with heterologous factor V antibody and no antigenic material has been found. Thus hereditary factor V deficiency probably represents a deficiency of factor V molecules, rather than the synthesis of a defective molecule.
Acquired Inhibitors of Factor V