[Cystathionine betasynthase and MTHFR deficiencies in adults]

Homocysteine lies at an important metabolic branch point; it may be either converted to cystathionine through the transsulfuration pathway, or methylated to form methionine. Hyperhomocysteinemia may result from hereditary defects affecting one of these reactions.

Cystathionine beta synthase or 5,10-methylenetetrahydrofolate deficiency can both result in homocystinuria. Current knowledge about biochemical mechanisms leading to hyperhomocysteinemia, clinical and radiological features, pathogenesis and treatment are reviewed, focusing on late onset forms of these diseases which can be diagnosed in adulthood. CBS deficiency is characterized by lens dislocation, skeletal abnormalities, neurologic disturbances and thromboembolism. MTHFR deficiency leads to various neurological symptoms, ranging from developmental delay to encephalopathy, including motor and gait abnormalities, seizures, psychiatric manifestations and rarely strokes. The treatment of CBS deficiency depends on vitamin B6, whereas MTHFR deficiency can be efficiently treated by vitamin B12, folic acid, and betaine.

Homocysteinemia should be measured in patients with unexplained neurological manifestations or thromboembolism.