ABSTRACT
Hyperhomocysteinemia is an established risk factor for deep vein thrombosis. Factor
V Leiden has been reported to potentiate the thrombotic risk related with severe hyperhomocysteinemia,
being more represented in thrombotic patients with homocystinuria as compared with
patients without a history of thrombosis. The results concerning the interaction between
moderate hyperhomocysteinemia and inherited thrombophilic factors such as Factor V
Leiden or the prothrombin G20210A mutation are contradictory. The relative risk for
venous thrombosis has been reported to be increased 10- to 50-fold in patients carrying
both hyperhomocysteinemia and inherited thrombophilia in comparison with normal controls,
suggesting a synergistic interaction, yet other studies failed to confirm such conclusion.
The heterogeneity of these findings is in part due to the small number of individuals
with double defects, leading to statistically unreliable results. Genotyping for mutations
that are possible causes of moderate hyperhomocysteinemia, such as the thermolabile
variant (C677T) of methylenetetrahydrofolate reductase (MTHFR), does not seem useful
to identify individuals at higher risk for venous thromboembolism. In fact, in most
of the studies the presence of the C677T MTHFR homozygous genotype does not increase
the thrombotic risk associated with Factor V Leiden or the prothrombin mutation.
KEYWORD
Hyperhomocysteinemia - venous thrombosis - inherited thrombophilia - Factor V Leiden
- prothrombin G20210A mutation