Hyperhomocysteinaemia as a risk factor for venous thrombosis: an update of the current evidence.

Classical homocystinuria is associated with arterial vascular diseases and venous thrombosis. In the last decade, many studies, including some prospective studies, have been published indicating that moderate hyperhomocysteinaemia is also a risk factor for venous thrombosis. The 677C>T mutation in the methylenetetrahydrofolate reductase (MTHFR) gene is an important cause of mild hyperhomocysteinaemia. Recent metaanalyses show an elevated risk of venous thrombosis for subjects with the TT-genotype. Based on the concept of 'Mendelian randomisation', this observation supports the hypothesis that hyperhomocysteinaemia is a causal risk factor for venous thrombosis. The results of one homocysteine-lowering trial regarding venous thrombosis are awaited at the end of 2003. In this paper the current evidence for hyperhomocysteinaemia as a risk factor for venous thrombosis is being discussed.