Background and Goal. The aim was to examine the serum levels of homocysteine (Hcy) and their associations with the methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism in patients with schizophrenia and mood disorders as well as controls. Materials and Methods. There were 198 patients: 82 with schizophrenia spectrum disorders, 22 with mood disorders, and 94 controls. The level of Hcy was determined by an isocratic high-performance liquid chromatography system. MTHFR C677T polymorphism was analysed using the restriction fragment length polymorphism-polymerase chain reaction method. Results. The average level of Hcy was μmol/L for patients with schizophrenia, μmol/L for patients with affective disorders, versus μmol/L in a control. The highest level of Hcy has been observed in patients with episodic-recurrent course of schizophrenia ( μmol/L), paranoid schizophrenia continuous ( μmol/L), and in patients with affective disorders ( μmol/L). An association between the MTHFR gene C677T polymorphism and Hcy level was found by linear regression analysis ( , ). Conclusions. The data indicate a link between Hcy levels and schizophrenia and mood disorders. No associations between the level of Hcy in patients with schizophrenia and mood disorders and the MTHFR C677T polymorphism were found. 1. Introduction Hcy was first described by Butz and du Vigneud in 1932 . They obtained the product by treating methionine with a concentrated acid. Three enzymes are directly involved in the Hcy metabolism: methionine synthase (MS), betaine homocysteine methyltransferase, and cystathionine β-synthase. Several other enzymes are indirectly involved. Vitamins B6 and B12 are cofactors to these enzymes, and folate is a substrate in the MS-mediated reaction . Deficiencies in vitamins B6, B12, and folate can lead to high Hcy levels. Supplementation with pyridoxine, folic acid, B12, or folic acid, respectively, reduces the concentration of Hcy in the bloodstream. Methionine is the immediate precursor of S-adenosylmethionine, the methyl donor of numerous methylation reactions in the brain, including many that are directly involved in the synthesis and metabolism of monoamines such as dopamine, norepinephrine, and serotonin . This suggests that an association between elevated Hcy and schizophrenia is biologically plausible. Another way of investigating the association between Hcy and mental disorders is via the MTHFR gene. MTHFR converts 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, which is needed for the remethylation of Hcy to methionine . MTHFR
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