The Role of Abnormalities Related to the One Carbon Cycle in Depression and Schizophrenia

This paper reviews our present knowledge of the role of the one-carbon cycle in mood disorder and schizophrenia with particular attention to S-adenosyl methionine (SAM). After an historical introduction the clinical data is first reviewed of the anti-depressant action of SAM, in particular a survey of double blind placebo-controlled trials. Then follows an account of the biochemical parameters of the action of SAM, in particular the role of folic acid and 5-methyltetrahydrofolate (vitamin B9), polyamines, homocysteine, together with epigenetic studies. In schizophrenia the effect of oral l-methionine on worsening the symptoms of some chronic schizophrenics has been known since 1961. Recent epigenetic research covered has addressed the mechanism of this reaction. This includes the role of SAM in modulating DNA methyltransferase-1 mRNA activity, cytosine 5-methylation, spine numbers and the expression of mRNAs encoding for reelin and GAD67 in GABAergic neurons in the frontal cortex in schizophrenia. There is also evidence that marker D8S542 located within the methionine sulfoxide reductase (MSRA) gene may be involved in schizophrenia as well as 677C > T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene. The possible roles of homocysteine and methionine S-adenosyl transferase kinetics are also discussed.