The MTHFR gene provides instructions for making an enzyme called methylenetetrahydrofolate reductase (MTHFR) . This enzyme plays a role in processing amino acids, the building blocks of proteins, and helps the body produce folate, which is necessary to create DNA. The MTHFR gene is located on chromosome 1 in humans. There are DNA sequence variants, or genetic polymorphisms, associated with this gene, and the most well-studied MTHFR polymorphism changes a single DNA building block in the MTHFR gene. Specifically, it replaces the nucleotide cytosine with the nucleotide thymine at position 677 (written as 677C>T) . This common variant results in a form of methylenetetrahydrofolate reductase that has reduced activity at higher temperatures. Mutations in the MTHFR gene can affect the body’s ability to process amino acids, which can lead to some adverse health outcomes. However, it is unclear how MTHFR gene changes might influence the development of neural tube defects. Each person has two copies of the MTHFR gene, and there are three possible genotypes: MTHFR 677 CC, MTHFR 677 CT, or MTHFR 677 TT. Having one variant (heterozygous) is less likely to contribute to health issues, while having two mutations (homozygous) may lead to more serious problems. There are two variants, or forms, of mutations that can occur on the MTHFR gene: C677T and A1298C.