Rare genetic defects that cause extremely high plasma homocysteine levels also cause CAD.14,15 It was therefore hypothesised that, even within the normal range of plasma homocysteine concentrations, higher levels may appreciably increase CAD risk.15 The enzyme methylene tetrahydrofolate reductase, encoded by the MTHFR gene, uses folate to metabolise and thereby remove homocysteine.16 The MTHFR C677T polymorphism is common (T-allele frequency 15–45%) in many populations and reduces enzyme efficiency. Here, MTHFR is linked to coronary artery disorder.