Prothrombin deficiency is an autosomal recessive disorder associated with a moderately severe
bleeding tendency. In this study, 13 patients with
prothrombin deficiency were screened for the presence of alterations in the
prothrombin gene, and nine novel candidate mutations were identified. Of 11 patients with
hypoprothrombinemia, ten are homozygous for five mutations and one patient is a compound heterozygote. The two patients with
dysprothrombinemia are homozygous for two mutations. Eight of nine mutations are missense ones associated with single amino acid substitutions in the propeptide (Arg-1Gln, Arg-2Trp), the kringle-1 (Asp118Try) and kringle-2 (Arg220Cys) domains and the catalytic
serine protease domain (Gly330Ser, Ser354Arg. Arg382His and Arg538Cys). The ninth mutation is an in-frame deletion of 3 bp that results in the omission of one
amino acid (del Lys 301/302). The combination of these missense mutations with crystal structures for
alpha-thrombin and the
prothrombin fragments 1 and 2 resulted in new insight into the function of
alpha-thrombin. The
hypoprothrombinemia mutations were inferred to affect either the cleavage of the propeptide from the Gla domain, the stability of the kringle-1 and -2 domains, or the close association of the A and B chains of the
serine protease domain. The
dysprothrombinemia mutations were inferred to directly affect catalytic function through their location at the active site crevice or exosite 1 within the
serine protease domain.