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About thrombosis
Thrombophilia: acquired thrombophilia
Hyperhomocysteinaemia
Homocysteine is an amino acid that, if present at a high level within the blood, is associated with an increased risk of arterial thrombosis, including heart attacks and strokes. This condition is known as hyperhomocysteinaemia. It is believed that high blood levels of homocysteine have a toxic effect, by damaging the lining of the blood vessels (known as the endothelium).
In contrast with the vast body of research conducted on the association between hyperhomocysteineaemia and arterial thrombosis, little research has been carried out to establish the risk of venous thrombosis for individuals with this condition. However, existing research indicates a very small but significant association between elevated homocysteine levels and a minor risk of venous thrombosis.
It is likely that on their own, raised levels of homocysteine are too minor a risk factor to cause any problems. However, this risk increases when it is combined with another risk factor, such as Factor V Leiden.
Considerable interest has focused on a mutation in the gene for one of the proteins that breaks down homocysteine. This gene is known as Methylenetetrahydrofolate reductase, or MTHFR.
If an individual has two MTHFR genes with what is known as the C677T variant, they are described as homozygotes for MTHFRC677T. This includes between 5 and 20 per cent of the population. People who are homozygotes for MTHFRC677T have a reduced ability to metabolise homocysteine, especially if they are deficient in folic acid.
Treatment of hyperhomocysteineaemia
Treatment includes giving supplements of folic acid, a vitamin present in
green vegetables. Clinical studies show that folic acid lowers homocysteine
levels by as much as 40 per cent. Vitamins B12 and B6 also have a minor effect
in reducing homocysteine levels.
Clinical studies also show that by reducing plasma homocysteine levels, there is an improvement in the function of the endothelium (lining of the blood vessels).
It is not yet known whether in the long term, folic acid supplementation will reduce the risk of heart attacks and strokes and this question is being addressed through ongoing clinical trials.
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