Treatment of CBS deficiency usually begins with a trial of oral vitamin B6 (pyridoxine) supplementation, with daily measurement of plasma amino acids. CBS requires pyridoxine as a coenzyme for enzymatic activity. Overall, about 25% of patients respond to large doses of pyridoxine, although the percentage may be lower for patients identified through newborn screening. This pyridoxine response usually coincides with the presence of some residual enzyme activity. Dietary restriction of methionine in conjunction with cystine supplementation reverses the biochemical abnormalities to some extent and appears to reduce the clinical symptoms. Special formulas are available commercially, but the diet is difficult to maintain long term. In an attempt to decrease homocysteine levels, folic acid, and betaine can be supplemented to induce recycling of this amino acid to methionine for alternate metabolism. Vitamin B12 (cobalamin) may also be helpful.
Because the diagnosis and therapy of homocystinuria is complex, the pediatrician is advised to manage the patient in close collaboration with a consulting pediatric metabolic disease specialist. It is recommended that parents travel with a letter of treatment guidelines from the patient’s physician.