FACTOR-V-LEIDEN (R506Q) AND RISK OF VENOUS THROMBOEMBOLISM - A CASE-CONTROL STUDY BASED ON THE SPANISH POPULATION

Resistance to activated protein C (APC) is a frequent cause of thrombo philia. Most patients showing APC-resistance have a G to A mutation at codon 506 of the factor V that converts arginine to glutamine. This m utation is present in populations worldwide with frequencies ranging f rom 0.01 to 0.05. Genotyping of 150 control individuals from the Spani sh population showed that 3.33% of them carried the mutation. Several studies have measured resistance to APC (following a classical functio nal assay) and have determined the factor V genotype in a number of th rombophilic patients, in an attempt to compare the predictive value of both laboratory methods. To assess the incidence of the factor V muta tion among Spanish thrombophilic patients, we genotyped 51 of these. T he frequency of mutation carriers rose from 3.33% in the controls to 5 3% in the patients. We found significant differences for the thrombosi s-free survival curves and for the age at the first thrombotic event b etween patients who carried or did not carry the mutation. Analysis of relatives of 16 patients who carried the factor V mutation suggests t he existence of additional genes that modulate the effect of the facto r V gene in the development of venous thrombosis among carriers of the G to A mutation.