Summary
Homocysteine may have a thrombogenic effect through inhibition of inactivation of
factor Va by activated protein C. Because factor V Leiden also leads to resistance
of factor V to activated protein C, it would be possible that both factors show interaction
for the risk of venous thrombosis. This has been reported in some studies, but not
in others. We performed a meta-analysis to investigate a possible interaction between
factor V Leiden and hyperhomocysteinemia, including 825 subjects with venous thrombosis
and 2,109 controls, for the risk of venous thrombosis. In addition, we assessed a
possible interaction between factor V Leiden and MTHFR 677TT genotype (the most common
genetic determinant of homocysteine levels), including 2,547 subjects with venous
thrombosis and 4,327 controls. We also investigated the interaction effect of factor
V Leiden and hyperhomocysteinemia in a large case-only study using data of the VITRO
study, including 2,077 subjects with first-time venous thrombosis. The meta-analysis
yielded no evidence for additive or multiplicative interaction between factor V Leiden
and hyperhomocysteinemia [relative excess risk due to interaction (RERI) –1.77 (95%CI
–8.61 to 5.08) and multiplicative interaction term 0.86 (95%CI 0.35 to 2.14)].The
case-only study also showed no interaction effect [0.58 (95%CI 0.29 to 1.16)]. Also
the metaanalysis on factor V Leiden and MTHFR 677TT yielded no evidence of interaction;
RERI 0.13 (95%CI –3.60 to 3.86) and multiplicative interaction term 1.23 (95%CI 0.72
to 2.11). Both the meta-analyses of published studies and a large case-only study
did not show evidence for interaction between factor V Leiden and hyperhomocysteinemia
for risk of venous thrombosis.
Keywords
MTHFR - Methylenetetrahydrofolatereductase - homocysteine - factor V Leiden - meta-analysis
- case-only - case-control - VITRO