When administered in recommended oral dosage to children or adults, Cystadane acts as a methyl group donor in the remethylation of homocysteine to methionine in patients with homocystinuria. As a result, toxic blood levels of homocysteine are reduced in these patients, usually to 20-30 percent or less of pre-treatment levels.

Elevated homocysteine blood levels are associated with clinical problems such as cardiovascular thrombosis, osteoporosis, skeletal abnormalities, and optic lens dislocation. Plasma levels of homocysteine were decreased in nearly all patients treated with betaine. In observational studies without concurrent controls, clinical improvement was reported by the treating physicians in about three-fourths of patients taking betaine. Many of these patients were also taking other therapies such as vitamin B₆ (pyridoxine), vitamin B₁₂ (cobalamin), and folate with variable biochemical responses. In most cases studied, adding betaine resulted in a further reduction of homocysteine.

Betaine was observed to lower plasma homocysteine levels in the three types of homocystinuria, i.e., cystathionine beta-synthase (CBS) deficiency; 5,10-methylenetetrahydrofolate reductase (MTHFR) deficiency; and cobalamin cofactor metabolism (cbl) defect.

Betaine has also been demonstrated to increase low plasma methionine and S-adenosylmethionine (SAM) levels in patients with MTHFR deficiency and cbl defect.

In CBS-deficient patients, large increases in methionine levels over baseline have been observed.

Betaine occurs naturally in the body. It is a metabolite of choline and is present in small amounts in foods such as beets, spinach, cereals, and seafood.

Pharmacokinetic studies of betaine are not available. Plasma levels of betaine have not been measured in patients and have not been correlated to homocysteine levels. However, pharmacodynamic measurements, i.e., monitoring of plasma homocysteine levels, have demonstrated that the onset of action of betaine is within several days and that a steady state in response to dosage is achieved within several weeks. Patients have taken betaine for many years without evidence of tolerance.

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