Table 9: Biochemical characteristics and treatment of homocysteine metabolism disorders.

Defective enzymeHomocysteine (U, P) Additional biochemical characteristicsTreatment

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) MethionineHigh-dose betaine
Methionine supplementation

  *(U): urine, (P): plasma.