At a Glance
Why Get Tested?
When to Get Tested?
When you have elevated homocysteine levels; sometimes when a close relative has MTHFR gene mutations or has developed CVD or thrombosis at an early age
A blood sample drawn from a vein in your arm
Test Preparation Needed?
The Test Sample
What is being tested?
When there are mutations or variations in the MTHFR gene, it can lead to serious genetic disorders such as homocystinuria, anencephaly, spina bifida, and others. The MTHFR enzyme is critical for metabolizing one form of B vitamin, folate, into another. It is also part of the process that converts homocysteine into methionine, an important building block for many proteins.
If someone has increased levels of homocysteine, that means the body is not processing it properly. One cause of that could be a mutation in the MTHFR gene, causing homocystinuria. While at least seven unique MTHFR mutations have been found in people with homocystnuria, there are two relatively common DNA sequence variants, known as single nucleotide polymorphisms (SNPs) that are tested. The two MTHFR variants are called C677T and A1298C, and individuals can inherit one or both variants. These SNPs result in changes in the DNA (or mutations) that are associated with increased homocysteine levels in the blood, which may increase the risk of premature cardiovascular disease (CVD), formation of inappropriate blood clots (thrombosis), and stroke.
Approximately 5-14% of the U.S. population is homozygous for C677T, meaning that they have two copies of it. There is some ethnic variability in the frequency, with the highest being in those of Mediterranean ancestry and the lowest in those of African ancestry.
The C677T variant results in a less active form of the MTHFR enzyme and reduced ability to process folate and homocysteine. When a person has two copies of the MTHFR C677T gene mutation (homozygous) or one copy of MTHFR C677T and one copy of A1298C (compound heterozygous), decreased MTHFR enzyme activity slows down the homocysteine-to-methionine conversion process and can lead to a buildup of homocysteine in the blood.
The increase in homocysteine is often mild to moderate but will vary from person to person depending upon the amount of MTHFR enzyme activity. Even if a person has two copies of the MTHFR mutation, that person may not develop high homocysteine levels since adequate folate intake can "cancel out" the effect of the MTHFR mutation.
Results of some studies suggest that high levels of homocysteine in the blood may contribute to risk of CVD by damaging blood vessel walls and promoting formation of plaque (atherosclerosis) and inappropriate blood clots. However, a direct link between homocysteine levels and cardiovascular disease or thrombotic risk has not been found. For more on this, see the article on Homocysteine.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
Ask a Laboratory Scientist
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
(Reviewed 2011 July). MTHFR. Genetics Home Reference. Available online at http://ghr.nlm.nih.gov/gene/MTHFR through http://ghr.nlm.nih.gov. Accessed February 2014.
(© 1995-2014). 5,10-Methylenetetrahydrofolate Reductase C677T, Mutation, Blood. Mayo Medical Laboratories. Available online at http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/81648 through http://www.mayomedicallaboratories.com. Accessed February 2014.
(© 2014). Methylenetetrahydrofolate Reductase (MTHFR) 2 Mutations 0055655. ARUP Laboratories Laboratory Test Directory. Available online at http://ltd.aruplab.com/Tests/Pub/0055655 through http://ltd.aruplab.com. Accessed February 2014.
Wang W. et al. (2013 March 11). MTHFR C677T Polymorphism and Risk of Congenital Heart Defects: Evidence from 29 Case-Control and TDT Studies. PLOS One. DOI: 10.1371/journal.pone.0058041. Available online at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0058041 through http://www.plosone.org. Accessed February 2014.
Hickey, S. et al. (3 January 2013). ACMG Practice Guideline: lack of evidence forMTHFR polymorphism testing. Genetics in Medicine. doi:10.1038/gim.2012. Available online at http://www.nature.com/gim/journal/v15/n2/full/gim2012165a.html through http://www.nature.com. Accessed February 2014.
Cohen D.A., et al. (29 November 2013). Laboratory informatics based evaluation of methylene tetrahydrofolate reductase C677T genetic test overutilization. Journal of Pathology Informatics. doi: 10.4103/2153-3539.122389. Available online at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3869957/ through http://www.ncbi.nlm.nih.gov. Accessed February 2014.
Mandava, P. et al. (Updated 2013 June 20). Homocystinuria/Homocysteinemia. Medscape. Available online at http://emedicine.medscape.com/article/1952251-overview#a30 through through http://emedicine.medscap.com. Accessed February 2014.
Sources Used in Previous Reviews
Mandava, P, et. al. (Updated 2009 May 25). Metabolic Disease and Stroke - Homocystinuria/Homocysteinemia. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/1162007-overview through http://emedicine.medscape.com. Accessed October 2010.
(Reviewed 2008 January). MTHFR. Genetics Home Reference [On-line information]. Available online at http://ghr.nlm.nih.gov/gene/MTHFR through http://ghr.nlm.nih.gov. Accessed October 2010.
Fong, C. (Revised 2010 February). Amino Acid and Organic Acid Metabolism Disorders. Merck Manual for Healthcare Professionals [On-line information]. Available online at http://www.merck.com/mmpe/sec19/ch296/ch296c.html?qt=MTHFR&alt=sh through http://www.merck.com. Accessed October 2010.
Hart, K. et. al. (Updated 2010 August). Hypercoagulable States – Thrombophilia. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/Thrombophilia.html?client_ID=LTD through http://www.arupconsult.com. Accessed October 2010.
(© 1995-2010). MayoClinic Mayo Medical Laboratories. Unit Code 91457: Methylenetetrahydrofolate Reductase (MTHFR) 2 Mutations [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/91457 through http://www.mayomedicallaboratories.com. Accessed October 2010.
(© 2006-2010). Methylenetetrahydrofolate Reductase (MTHFR) 2 Mutations: 0055655. ARUP's Laboratory Test Directory [On-line information]. Available online at http://www.aruplab.com/guides/ug/tests/0055655.jsp through http://www.aruplab.com. Accessed October 2010.
Varga, E. et. al. (2005 May 17). Homocysteine and MTHFR Mutations, Relation to Thrombosis and Coronary Artery Disease. Circulation. 2005;111:e289-e293 [On-line information]. Available online at http://circ.ahajournals.org/cgi/content/full/111/19/e289 through http://circ.ahajournals.org. Accessed October 2010.
Curtin, K. et. al. (2004 February). MTHFR C677T and A1298C Polymorphisms. Cancer Epidemiology, Biomarkers & Prevention. February 1, 2004 13; 285 [On-line information]. Available online at http://cebp.aacrjournals.org/content/13/2/285.full through http://cebp.aacrjournals.org. Accessed October 2010.
(2005 June 17). MTHFR Gene Variants and Birth Defects. CDC Birth Defects [On-line information] Available online at http://www.cdc.gov/ncbddd/bd/mthfr.htm through http://www.cdc.gov. Accessed October 2010.
(© 2010). MTHFR DNA Test. Kimball genetics [On-line information]. Available online at http://www.kimballgenetics.com/tests-mthfr.html through http://www.kimballgenetics.com. Accessed October 2010.