MTHFR enzyme converts 5

MTHFR enzyme converts 5,10-methylenetetrahydrofolate to 5-methyltetrafolate. Then, 5-methyltetrafolate is converted into THF by Methionine synthase. At this point methyl group is transferred to homocysteine leading to the formation of methionine. Methionine on the other hand is an important precursor for the biosynthesis of SAM. Being an important mediator of DNA methylation Sam also donates methyl groups in numerous biosynthesis reactions. Adenine and Cytosine DNA methylation is involved in DNA replication and arrangement in prokaryotes.
DNA-methylation reaction is catalyzed by DNA methyl-transferase enzyme that transfer methyl groups from SAM to cytosine.
Thus, Any mutations in MTHFR gene lead to defects in SAM metabolism.