Homocysteine, S-Adenosylmethionine and S-Adenosylhomocysteine

Homocysteine and the related metabolites S-adenosylmethionine and S-adenosylhomocysteine play a vital role in several vital biological processes. Disturbed levels are found in inborn errors of methionine metabolism as well as in other pathological states such as vitamin B12 or folate deficiency and renal disease. The association of moderately elevated Hcy and several diseases, particularly various forms of vascular disease has been extensively studied and documented although a role in causation is controversial. Associations with neural tube defects, neuropsychiatric disorders, impaired cognitive function, dementia and osteoporosis have also been implicated. Plasma total homocysteine is measured in many routine laboratories employing various methods. The laboratory measurement of S-adenosylmethionine and S-adenosylhomocysteine in plasma plays an increasing role in studies of pathogenesis of elevated homocysteine as well as the differential diagnosis of hypermethioninaemia due to deficiencies of methionine adenosyltransferase, glycine methyltransferase or S-adenosylhomocysteine hydrolase. Those methods that are often available in laboratories involved in the investigation of inborn errors of metabolism namely HPLC and tandem mass spectrometry are described in detail in this chapter.