Prothrombin Segovia: a new congenital abnormality of prothrombin.

A family with a new congenital dysprothrombinemia is presented. The propositus is a 21-yr-old man who presented simultaneously with hemartrosis of the left knee and an extensive hematoma following a minor trauma. Prothrombin time and activated partial thromboplastin time were prolonged. Prothrombin activity was very low when measured by biological assay using physiological activators (7% by one-stage method and 20% by two-stage method) or a Russel's viper venom-cephalin mixture (23%), Notechis scutatus scutatus venom (15%) and Echis carinatus venom (17%); in contrast, the level was found to be borderline to normal using Taipan viper venom (64%) and normal by both staphylocoagulase and immunologic methods. Family studies revealed consanguinity between the propositus' mother and father and both presented a 50% reduced prothrombin level when physiological activators or Echis carinatus viper venom were used. A line of identity between normal and abnormal prothrombin was observed on immunodiffusion. The migration of the abnormal prothrombin was less anodic and was not changed by the addition of calcium. The patient's serum showed 3 bands in the bidimensional immunoelectrophoresis system, whereas normal serum showed only 2 bands. The term prothrombin Segovia is proposed to define this new prothrombin abnormality.