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Genetic and Rare Diseases Information Center (GARD)

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MTHFR gene mutation


* Not a rare disease
Other Names for this Disease
  • Methylenetetrahydrofolate reductase mutation
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Your Question

I have recently been diagnosed with the C677T heterozygous gene mutation. What I would most like to know is: does this mutation have any bearing or is it something I do not need to concern myself with? 

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What is a MTHFR gene mutation?

The MTHFR gene provides the instructions for making the MTHFR enzyme, which plays a role in converting the amino acid homocysteine to methionine. A change in a gene is called a mutation or a polymorphism. Some changes in the MTHFR gene are very common, such as the C677T mutation or the A1298C mutation. These mutations result in a version of the MTHFR enzyme that has a mildly to moderately reduced function. There are also rare mutations in the MTHFR gene that severely impair the enzyme and cause a rare disease called homocystinuria.[1] 

People with a personal or family history of heart disease or blood clots may be tested for the common MTHFR gene mutations. Because each person has two copies of the MTHFR gene, it is possible to have one or two MTHFR gene mutations. If you have two mutations, you are said to be homozygous. If you have one mutation, you are heterozygous. Individuals with two C677T mutations and people with one C677T and one A1298C mutation have an increased risk of developing blood clots. Having this increased risk does not mean that a person will develop a clot, as many people with MTHFR gene mutations never do.[1]
Last updated: 9/18/2012

Does having one C677T mutation in the MTHFR gene increase a person's risk of developing blood clots?

Having one mutation in the MTHFR gene is not associated with an increased risk of blood clots, because it does not lead to high levels of homocysteine in the blood. Having two C677T mutations can result in high homocysteine levels. People with high levels of homocysteine are at increased risk for blood clots and hardening of the arteries (atherosclerosis).
Last updated: 9/18/2012