Summary
Fibrinogen Matsumoto I is a novel hereditary dysfibrinogen identified in a 1-year-old
boy with Down’s syndrome. Though he showed no apparent bleeding or thrombotic tendency,
he had a congenital heart disease. Preoperative coagulation tests of his plasma revealed
a prolonged thrombin time and the fibrinogen level determined by the thrombin time
method was markedly decreased. Molecular weight of fibrinogen chains showed apparently
normal Aα, Bβ-, and γ-chains. The rate of fibrinopeptide release was normal, whereas
fibrin polymerization was delayed. Fibrinogen γ-chain gene fragments from the propositus
were amplified by polymerase chain reaction then sequenced. The triplet GAT, coding
for the amino acid residue γ364, was replaced by CAT, resulting in the substitution
of Asp→His. This residue is adjacent to the Tyr-363 that is demonstrated to be the
primary site for fibrin polymerization. Our results indicate that the residue γ364
Asp is essential for normal polymerization of fibrin monomer.