Homocysteine is a sulfur containing amino acid that results from the demethylation of the essential amino acid methionine. Hyperhomocystinaemia refers to an increase in the concentration of homocysteine in plasma above normal and homocystinuria to the presence of homocystine (the disulfide form of homocysteine) in the urine. Homocystinuria only occurs when plasma levels of homocysteine are significantly raised. A number of inherited and acquired disorders may cause a high level of homocysteine. In this chapter we provide case reports that exemplify the wide phenotypic variability that can occur with these conditions and then discuss these and other disorders in more detail.
KeywordsHomocystinuria Homocystine Homocysteine Cystathionine beta-synthase deficiency Hyperhomocysteinaemia
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