Frequency of polymorphisms in the B-domain of factor V gene in APC-resistant patients

In this study we investigated a group of patients in whom a resistance to APC (activated protein C) was found but no Leiden mutation existed in the presence of missense mutations in the first 1200 bp of the Exon 13 (B-domain) in the factor V (FV) gene. The determination of the APC response was performed using the Immunochrom(R) APC response Test Kit. The mutations were determined by temperature gradient gel electrophoresis and DNA sequencing. In the APC-resistant patients without the FV Leiden, we found 4 silent mutations (2298CT, 2325TC, 2379AG, 2391AG) and 4 missense mutations (2540AC, 2663AG, 2684AG, 2863AG), which code for the amino acids N789T (GenBank Accession # AF119360), K830R, H837R, and K897E. In all of the patients and controls, the polymorphisms at nucleotide positions 2391, 2663, 2684, and 2863 appeared to be associated. In the major allele all bases are A (A allele) and in the minor allele are G (G allele). A significantly lower G allele frequency was observable in the patient group than in the control group (0.14 vs. 0.31; p0.05). The frequency of the 2540C allele, which is associated with the 2379G and the 4070G allele (non-Leiden!), did not differ significantly between the patient and the control groups. We suggest that the G allele, which is not associated with the FV Leiden mutation, as well as the [2379G; 2540C; 4070G] allele have no influence on the APC cofactor function itself, or only subtly as determined in the test systems used.