Test Background HCY is a thiol-containing amino acid produced by the intracellular demethylation of methionine. Deficiency of crystathionine β-synthase or N5-methyltetrahydrofolate reductase causes homocystinuria. Folic acid and vitamins B6 and B12 serve as cofactors for the enzyme N5-methyltetrahydrofolate reductase and insufficiency of any of these, or indeed aberrant enzyme catalysis and the resultant hyperhomocysteinaemia, has been implicated in cardiovascular disease (it is thought that this reflects the increased incidence of thrombotic events).
Clinical Indications Presentation of infantile homocystinuria (ie. crystathionine β-synthase/methyltetrahydrofolate reductase deficiency): ocular (myopia, detached retina), skeletal (osteoporosis, genu valgum, vertebral abnormality) as well as vascular complaints (arterial/venous thromboses) Risk stratification in patients in whom premature vascular disease, CVA and thrombosis is apparent