Table 9.

Biochemical characteristics and treatment of homocysteine metabolism disorders.

Defective enzyme	Homocysteine (U, P)	Additional biochemical characteristics	Treatment
Cystathionine beta-synthase (CBS)	↑	↑ Methionine ↓ Cysteine	Pyridoxine, B12, folate Methionine-restricted diet Cysteine supplementation betaine
Methionine synthase (MTR)	↑	Normal or ↑ Folate Normal or ↑ Cobalamin	High-dose hydroxycobalamin
Methylene tetrahydrofolate reductase (MTHFR)	↑	↓ Methionine	High-dose betaine Methionine supplementation

  *(U): urine, (P): plasma.