Methylenetetrahydrofolate reductase or MTHFR is a gene. Every person carries two copies of this gene, one from each parent. Gene mutations occur when there is a variant in a gene's DNA coding. There are many MTHFR mutations, but the two most common variants are C677T and A1298C. People diagnosed with an MTHFR variant have a mutation in either one or both copies of their MTHFR gene.
MTHFR mutations occur in people all around the world. Varients are fairly common, and the chance of having a mutation in the least one MTHFR gene is as high as 50 percent for some ethnicities. Between 10 and 15 percent of Caucasians and more than 25 percent of Latinos have variants in both MTHFR genes.
The MTHFR gene creates an enzyme that plays an important role in processing amino acids. Specifically, it helps the body break down an amino acid called homocysteine. B vitamins such as folic acid break down homocysteine into another amino acid — methionine, which is used to make proteins and other compounds. This process leaves little homocysteine in the blood.
MTHFR variants change the genetic code. In some people, this causes the enzyme this gene produces to be less effective and allows homocysteine to build up in the blood. Homocysteine levels are more likely to rise when someone has two copies of the C677T variant. Most people with MTHFR variants have normal homocysteine levels.
One of the conditions resulting from an MTHFR mutation is homocystinuria. The body is unable to process both homocysteine and methionine, and this causes abnormal clotting, eye problems, learning problems, and skeletal abnormalities, though how it causes them is not yet understood. As the homocysteine builds up in the blood, it is excreted in the urine.
Women with some MTHFR mutations have an increased risk of having a baby with a neural tube defect, a birth defect that occurs during the development of the fetal brain and spinal cord. One of the most common types of neural tube defects is anencephaly, a condition in which parts of the brain or skull do not fully develop. Another condition that might result is spina bifida, when the spinal column does not completely close around the nerves of the spinal cord. This malformation leaves a part of the spinal cord sticking out and causes permanent damage.
Some studies suggest that MTHFR variants are linked to many medical problems, including heart disease, stroke, clotting problems, autism, psychiatric disorders, and some types of cancer. That said, having an MTHFR mutation does not increase a person's risk for these conditions, and the mutation's role in them is unknown.
For people with high homocysteine, MTHFR testing can confirm if a mutation is the cause. Unless the patient has very high levels of homocysteine, most doctors do not recommend testing for varients. Most people with an MTHFR mutation are at low risk, and knowing the variant does not change the treatment approach.
MTHFR mutations rarely cause very high levels of homocysteine. As such, people presenting with high levels are evaluated for other conditions that can cause it. These include hypothyroidism, obesity, high cholesterol, hypertension, smoking, advanced age, and some medications. High homocysteine levels can also result from folate and vitamins B6 and B12.
Despite the link between the enzyme created by the MTHFR gene and folate, taking extra folate does not benefit someone with an MTHFR variant, though it is still important to get the recommended daily amount. All pregnant women need to get the recommended amount of folate, and current clinical guidelines do not indicate that pregnant women with known MTHFR mutations need extra. Women who have a family history or a previous child with a neural tube defect should discuss folate supplementation with their doctors.
Treatments for an MTHFR mutation vary greatly depending on the patient's circumstances. In many cases, an MTHFR mutation in and of itself does not require treatment. As homocysteine levels can rise for many other reasons, it is important to identify the cause of the problem. High-dose folate supplements can mask a vitamin B12 deficiency, so it is important to check for this as this deficiency can cause serious and permanent problems.
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