This gene encodes the coagulation factor XIII A subunit.Coagulation factor XIII is the last zymogen to become activated in the blood coagulation cascade.Plasma factor XIII is a heterotetramer composed of 2 A subunits and 2 B subunits.The A subunits have catalytic function, and the B subunits do not have enzymatic activity and may serve as plasma carrier molecules.Platelet factor XIII is comprised only of 2 A subunits, which are identical to those of plasma origin.Upon cleavage of the activation peptide by thrombin and in the presence of calcium ion, the plasma factor XIII dissociates its B subunits and yields the same active enzyme, factor XIIIa, as platelet factor XIII.This enzyme acts as a transglutaminase to catalyze the formation of gamma-glutamyl-epsilon-lysine crosslinking between fibrin molecules, thus stabilizing the fibrin clot.It also crosslinks alpha-2-plasmin inhibitor, or fibronectin, to the alpha chains of fibrin.Factor XIII deficiency is classified into two categories: type I deficiency, characterized by the lack of both the A and B subunits, and type II deficiency, characterized by the lack of the A subunit alone.These defects can result in a lifelong bleeding tendency, defective wound healing, and habitual abortion.[provided by RefSeq]