evidence: Every person has a gene that produces an enzyme called methylenetetrahydrofolate reductase (MTHFR gene), which converts folic acid into its active form folate, also called vitamin B9. This gene helps repair DNA and remove free radicals. People with some rare mutations in the gene may have an increased risk of developing skeletal and neurological problems or blood clots, due to a reduction in MTHFR enzyme activity. However, most of the common MTHFR mutations either do not affect enzyme activity or only require individuals with the mutation to supplement their diets with folic acid. No scientific evidence supports the claim that mutations in the MTHFR gene are associated with either birthmarks or a higher risk of adverse reactions to vaccines.