ABSTRACT
BACKGROUND: Factor (F)XIII B-subunit, which plays a carrier role for zymogen FXIIIA, is highly polymorphic, but the molecular basis for these polymorphisms and their relationship to disease remains unknown. OBJECTIVES: To screen the FXIIIB gene coding region for common variation and analyze possible functional effects. METHODS AND RESULTS: We examined the FXIIIB gene by PCR-SSCP and identified three common single nucleotide polymorphisms: A8259G, C29470T and A30899G. A8259G results in substitution of His95Arg in the second Sushi domain. An FXIII tetramer ELISA was developed to analyze B-subunit dissociation from A-subunit (leading to access to the catalytic site of FXIII). Increased subunit dissociation, 0.51 vs. 0.45 (fraction of total tetramer), was found in plasma from subjects possessing the Arg-allele. However, when the variants were purified to homogeneity and binding was analyzed by steady-state kinetics, no difference was observed. The relationship between His95Arg and venous thrombosis was investigated in 214 patients and 291 controls from Leeds. His/Arg + Arg/Arg genotypes were more frequent in patients than controls (22.4% vs. 15.1%). His95Arg was also investigated in the Leiden Thrombophilia Study, in which a similar difference was observed for 471 patients vs. 472 controls (18.5% vs. 14.0%), for a pooled odds ratio (OR) of 1.5 (CI95 1.1-2.0). CONCLUSIONS: We have identified three FXIIIB polymorphisms, one of which codes for substitution of His95Arg. The Arg95 variant associates with a moderately increased risk for venous thrombosis, and with increased dissociation of the FXIII subunits in plasma, although in vitro steady-state binding between purified subunits was not affected.
Subject(s)
Factor XIII/genetics , Polymorphism, Single Nucleotide , Thromboembolism/genetics , Venous Thrombosis/genetics , Binding Sites , Factor XIII/chemistry , Factor XIII/isolation & purification , Female , Gene Frequency , Genetic Testing , Genotype , Heterozygote , Homozygote , Humans , Kinetics , Male , Mutation , Phenotype , Protein Structure, Tertiary/genetics , Risk Factors , Thromboembolism/etiology , Venous Thrombosis/etiologyABSTRACT
Platelets from patients with beta-thalassemia/hemoglobin E, both splenectomized and nonsplenectomized cases, were examined in comparison to those from normal subjects by scanning electron microscopy. In normal subjects, the majority of platelets were discoid (mean +/- SD, 81.0 +/- 3.9%) with 17.3 +/- 3.5% type I spherical shapes (platelet with long axis/short axis greater than 1.1) and 1.3 +/- 1.0% type II (long axis/short axis = 1.0-1.1). The thalassemic patients had significant lower percentage of discoid platelets (60.9 +/- 8.1% in nonsplenectomized patients, 49.2 +/- 9.1% in splenectomized patients) and increase in spherical platelets (nonsplenectomized patients had 36.6 +/- 8.3% type I, 4.0 +/- 1.5% type II; splenectomized patients had 43.4 +/- 7.9% type I, 8.3 +/- 4.5% type II). Study of platelet reversibility from pseudopods to smooth surface showed that thalassemic platelets had poorer reversibility than normal platelets. Splenectomized patients had lower platelet pseudopod reversibility than nonsplenectomized cases. The shape changes and impaired reversibility of platelet pseudopods may be associated with the high tendency of pulmonary thrombus in beta-thal/HbE patients.
