MTR (5-Methyltetrahydrofolate-Homocysteine Methyltransferase): MTR is a critical enzyme involved in the remethylation pathway of homocysteine metabolism. It catalyzes the transfer of a methyl group from 5-methyltetrahydrofolate (5-MTHF) to homocysteine, producing methionine and tetrahydrofolate (THF). Methionine is a precursor for S-adenosylmethionine (SAM), a universal methyl donor essential for various methylation reactions in the body, including DNA methylation, neurotransmitter synthesis, and histone modification. Proper MTR activity is vital for maintaining normal homocysteine levels and supporting cellular methylation processes. Dysregulation of MTR, often due to genetic mutations or deficiencies, can impact these critical functions.