Polymorphism of the A subunit of coagulation factor XIII: evidence for subtypes of the FXIIIA*1 and FXIIIA*2 alleles.

Agarose gel isoelectric focusing (pH 5--6.5) in the study of plasma factor XIII (FXIII) polymorphism revealed heterogeneity characterized by a narrow or broad type of the electrophoretic band of the A subunit (FXIIIA). Isoelectric focusing in polyacrylamide gels supplemented with 2 M urea could clearly discriminate three different patterns in each of the two homomeric dimers, FXIIIA 1 and FXIIIA 2. These patterns can be explained by the existence of two codominant subtypes in each of the two common alleles, FXIIIA1 and FXIIIA2. These subtypes are termed FXIIIA1A, 1B, 2A, and 2B, respectively. In random population samples of Japanese, all the possible phenotypes deduced from the four codominant alleles were observed except for the FXIIIA 2A homozygote with the least frequency. This hypothesis is compatible with the segregation study on 35 family samples. The frequencies of the four alleles were calculated in 433 unrelated Japanese as being .2748 for FXIIIA1A, .6201 for FXIIIA1B, .0069 for FXIIIA2A, and .0982 for FXIIIA*2B. The data obtained in this study will contribute much more to disputed paternity cases and to anthropological surveys than will the former FXIIIA system with two common alleles.