Dr. Yee (USA) provided the audience with a general state of the art overview on the three-dimensional structure of Factor XIII A subunit (FXIII-A) which was an introduction to some of the problems elaborated by other speakers.

Dr. Greenberg (USA) elaborated how site-directed mutagenesis could be utilized to study the biochemical mechanism of FXIII activation and inactivation. As an example he used mutations at the Ca²⁺ binding site of FXIII-A to demonstrate the usefulness of such an approach in studying structural-functional relationship in the mechanism of the activation process.

Dr. Adany (Hungary) gave a detailed methodological overview on measuring the gene expression by quantitative PCR, in general, and measuring the expression of FXIII-A, in particular. She demonstrated how to overcome technical difficulties and how to complete the findings with morphological techniques by monitoring the expression of FXIII-A during the process of differentiation of monocytes into macrophages.

Dr. Bishop (USA) demonstrated the biochemistry of gelatin cross-linking by activated FXIII (FXIIIa) and the techniques by which the altered physicochemical characteristics of non-fibrin gel can be studied.

Dr. Ichinose (Japan) gave an overview of FXIII deficiencies and proposed a new classification. He proposed to abandon the terms FXIII type I and type II deficiency and replace it with FXIII-A, FXIII-B and, if such a case is found, combined subunit deficiency. Subcommittee members agreed with the proposal and by a unanimous vote suggested supplementing the formerly accepted, but not yet published, paper on FXIII nomenclature with the new classification.

Dr. Muszbek (Hungary) demonstrated a new one-step sandwich ELISA method that made it possible to measure the mass concentration of tetrameric plasma Factor XIII without any interference from free FXIII subunits, fibrinogen and other plasma components . He used this method to establish a reference interval for plasma FXIII mass concentration for the first time.

Dr. Grant (UK) summarized the findings of his group on Val34Leu FXIII-A polymorphism as a risk factor for arterial and venous thrombosis and showed the importance of its relationship to the expression of PAI-I. Dr. Balogh (Hungary) presented a study in which no increased risk for venous thrombosis could be related to this polymorphism.

Dr. Ariens (UK) presented data showing that the thrombin-induced release of activation peptide from plasma FXIII containing the mutant A subunit proceeded significantly faster than from the wild type plasma factor. The Finnish group (Wartiowara et al.) reported similar results for cellular FXIII. In three very recent publications it was reported that FXIII containing 34Leu allele had higher activity than wild type (Val/Val) FXIII. Evidence was presented that showed that this is not the case. Although in the mutant thrombin activation proceeds faster, fully activated mutant and wild type FXIII had identical specific activities.

At the previous subcommittee meeting it was decided to explore the possibility of preparing a reference plasma for FXIII measurement. Dr. Longstaff (UK) looked into this matter; however, FXIII did not present the required stability in the plasma preparations he investigated. It was agreed that a reference plasma would be essential for calibrating present and further assays and further effort is to be made in this direction.