Association of factor V deficiency with factor V HR2.
OBJECTIVE
Factor V HR2 possesses decreased co-factor activity to activated protein C and an increased ratio of factor V1 to factor V2. Factor V HR2 is associated with a mild increase in the risk of venous thromboembolism although not all studies concur on this point.


METHODS
Inconsistencies in results of the epidemiological studies may stem from a failure to identify other variables in factor V which might contribute to an increased risk of thrombosis in selected HR2 carriers. The aim of this study was to establish whether factor V deficiency increases the risk of venous thromboembolism when associated with HR2.


RESULTS
Four hundred and ninety-seven patients with venous thromboembolism and 498 controls were studied. HR2 was present in 12.5% of patients and 10.4% of controls. Factor V deficiency was associated with HR2 in 4.6% of patients and 1.0% of controls. The OR for venous thromboembolism in individual with HR2 alone was 1.2 (95% CI 0.8-1.8), while it was 4.7 (95% CI 1.8-12.5) for those with HR2 plus factor V deficiency.


CONCLUSIONS
Patients with HR2 and factor V deficiency developed a thrombotic event earlier (median age 35 years) than patients with HR2 alone (median age 43 years, p = 0.018). Double heterozygosity for HR2 and a factor V defect, including factor V deficiency, increased the thrombotic risk afforded by HR2.
Angelo Bianchi Bonomi Hemophilia and Thrombosis Center, IRCCS Maggiore Hospital and Department of Internal Medicine, University of Milan, Italy.
Elena M
EM
Faioni
Giancarlo
G
Castaman
Daniela
D
Asti
Federico
F
Lussana
Francesco
F
Rodeghiero
D020413:3' Untranslated Regions; D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000368:Aged; D005165:Factor V / Q000032:analysis / Q000737:chemistry / Q000235:genetics*; D005166:Factor V Deficiency / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics*; D005260:Female; D005787:Gene Frequency; D020022:Genetic Predisposition to Disease; D005820:Genetic Testing; D005838:Genotype; D006239:Haplotypes / Q000235:genetics; D006801:Humans; D007558:Italy / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011110:Polymorphism, Genetic; D011516:Prothrombin / Q000235:genetics; D012307:Risk Factors; D013923:Thromboembolism / Q000453:epidemiology / Q000209:etiology; D019851:Thrombophilia / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics*; D020246:Venous Thrombosis / Q000453:epidemiology / Q000209:etiology
D020413:3' Untranslated Regions; C095381:factor V Leiden; D005165:Factor V; D011516:Prothrombin