Homocystinuria was first reported in 1962 by Carson, Neill, and colleagues. Two years ago, the enzymatic defect was identified.
Homocystinuria is an autosomal recessive condition caused by a deficiency of the enzyme cystathionine-β-synthase (CBS), which leads to the deficiency of cystathionine and cysteine and the accumulation of homocysteine and methionine.
The diagnosis of homocystinuria is based on the recognition of the clinical phenotype in conjunction with the identification of an elevated total plasma homocysteine and elevated plasma methionine concentrations (via quantitative plasma amino acid analysis). Low cystine and low cystathionine are also seen. In addition, increased urinary excretion of homocysteine as well as cysteine-homocysteine disulfide can be identified on urine amino acid analysis. Confirmation of the diagnosis can be done via enzyme assay, typically performed on cultured skin fibroblasts, lymphocytes, liver tissue or via molecular studies.
The goal of the management of homocystinuria is to reduce or normalize plasma homocysteine concentrations.
- Pyridoxine or vitamin B6: This is a natural substance which helps change homocysteine into cysteine in the body. Few patients with homocystinuria respond well to vitamin B6 supplements. After a trial of vitamin B6 the homocysteine level is measured by a blood test.
- Vitamin B12: Also, a natural substance found in the body. It converts an excess of homocysteine back into methionine. Vitamin B12 is taken by orally in the form of pills.
- Folic acid: Another natural substance found in the body. It helps vitamin B12 change homocysteine back into methionine.
- Betaine: For some a betaine supplement helps in lowering the homocysteine levels by changing homocysteine back to methionine.
- Other medications: Other medications are also available to treat symptoms and complications related to homocystinuria. The most used medication that may be prescribed is an anticoagulant to prevent clots from forming in the blood.
Intake of foods containing protein must be limited for those whose amino acid levels do not react to vitamin B6. Dieticians may help in maintaining the diet. To meet the protein requirement for body growth and repair, the patient must depend on commercially available methionine-free special medical formulae. These provide all the nutrients and protein normally obtained from high-protein food. To prevent complications, the patient must adhere to this special formula for life.