Betaine

Homocystinuria is a hereditary disorder characterized by high levels of the amino acid homocysteine. This condition can be caused by deficiencies or defects in cystathionine beta-synthase (CBS), 5,10-methylenetetrahydrofolate reductase (MTHFR), and cobalamin cofactor metabolism (cbl). CBS converts homocysteine to cystathionine, and a deficiency in this enzyme can lead to an accumulation of homocysteine. MTHFR is responsible for producing 5-methyltetrahydrofolate, a methyl donor that participates in the conversion of homocysteine back to methionine; therefore, an MTHFR deficiency can also lead to homocystinuria. Additionally, a defect in cobalamin (vitamin B12) cofactor metabolism can lead to homocystinuria, since a metabolite of cobalamin (methylcobalamin) promotes the conversion of homocysteine to methionine.

Betaine transfers a methyl group via the enzyme betaine homocysteine methyl transferase (BHMT), converting homocysteine back into methionine and dimethylglycine (DMG). In patients with homocystinuria, betaine reduces homocysteine levels and improves health outcomes.