No specific cure has been discovered for homocystinuria; however, many people are treated using high doses of vitamin B₆ (also known as pyridoxine).^[1] Slightly less than 50% respond to this treatment and need to intake supplemental vitamin B₆ for the rest of their lives. Those who do not respond require a low methionine diet, and most will need treatment with trimethylglycine. A normal dose of folic acid supplement and occasionally adding cysteine to the diet can be helpful.

Betaine (N,N,N-trimethylglycine) is used to reduce concentrations of homocysteine by promoting the conversion of homocysteine back to methionine, i.e. increasing flux through the re-methylation pathway. The re-formed methionine is then gradually removed by incorporation into body protein. The methionine that is not converted into protein is converted to S-adenosyl-methionine which goes on to form homocysteine again. Betaine is, therefore, only effective if the quantity of methionine to be removed is small. Hence treatment includes both betaine and a diet low in methionine. In classical homocystinuria (CBS, or cystathione beta synthase deficiency) the plasma methionine usually increases above the normal range of 30 micromoles/L and the concentrations should be monitored as potentially toxic levels (more than 400 micromole/l) may be reached.

Low-protein food is recommended for this disorder, which requires food products low in particular types of amino-acid (e.g. methionine).

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