The relationship between homocysteine (HCY) levels and cognitive impairments, particularly executive functions in bipolar disorder (BD), has recently been investigated. However, conflicting results were reported. The aim of the present study is to investigate changes in serum HCY, methionine, vitamine B12 and levels in BD patients are relative to controls and to investigate the relationship between HCY, methionine, vitamin B12, and folate levels and clinical features, cognitive functions and psychosocial functioning in euthymic BD patients and controls. Methods: Sixty BD type I euthymic patients and twenty controls were assessed with Global Assessment of Functioning and a battery of neuropsychological tests including the Wisconsin card sorting test, the Rey's auditory verbal learning test, the Cancellation test, Trail making test A, Trail making test B, and the Stroop test. HCY, vitamin B12, methionine and folate levels were measured together after collecting blood samples from both patient and controls. Results: Mean serum methionine concentration was different between groups. Low serum methionine was found to be a predictor of BD. However, a statistically significant difference was not detected between groups for mean serum values of HCY, folate, or vitamin B12. HCY levels showed a positive correlation with illness duration, the number of total episodes, and the number of manic episodes. A significant correlation was not found between HCY, methionine, folate, B12 levels with cognitive functions and functioning in the BD group. Conclusion: Low serum methionine was found to be a predictor of BD, a condition which can lead to a decrease in SAM synthesis and thus to a variety of complications in methylation reactions. Additional studies are needed to clarify the impact of single carbon metabolism on BD.
