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Keywords:

  • bipolar disorder;
  • cognition;
  • homocysteine;
  • neuropsychological functioning

Objectives:  Elevated homocysteine (Hcy) levels have been demonstrated to have a negative impact on cognitive functioning in healthy elderly people. Further studies suggest that they are an independent risk factor for dementia, in particular for Alzheimer's disease. Bipolar disorder is also associated with cognitive impairment. However, the pathophysiological mechanisms of these deficits have not been elucidated yet. This study examines the role of Hcy on cognition and its impact on psychosocial functioning in euthymic bipolar patients.

Methods:  A total of 55 euthymic bipolar patients and 17 healthy controls were enrolled in the study. Neuropsychological assessments consisted of the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), the Trail Making Test (TMT), the Weschler Adult Intelligence Scale, 3rd edition (WAIS-III) subtest Letter–Number Sequencing Test (LNST) and the HAWIE-R (German version of the WAIS-R) subtest Information. Psychosocial functioning was assessed using the Social Adjustment Scale (SAS). To obtain plasma levels of Hcy, blood samples were collected in EDTA tubes, immediately put on ice, centrifuged within 15 min and stored at −80°C. Total Hcy concentration was measured using high-performance liquid chromatography.

Results:  In the neuropsychological tests, patients differed significantly from healthy controls on the TMT B and the RBANS composite indices Language, Attention and Total Score. No differences were found on the HAWIE-R subtest Information, the TMT A, LNST or the RBANS composite indices Immediate Memory, Visuospatial/Constructional Abilities and Delayed Memory. Mean Hcy levels were 9.8 ± 3.2 μm/L in the patient group and 7.8 ± 2.1 μm/L in the control group, respectively (p = 0.012). In the patient group Hcy levels significantly correlated with gender, diagnosis and RBANS index scores for Immediate Memory, Language, Attention and Total Score. Linear regression analyses revealed a significant and independent association of Hcy levels with Immediate Memory and TMT B scores in the patient group. Homocysteine levels did not correlate with any measure in the control group. Spearman's correlations indicated that psychosocial functioning in bipolar patients is not associated with clinical variables apart from time in remission. However, it correlated significantly with working memory measures (LNST). No relationship could be determined between psychosocial functioning and Hcy plasma levels.

Conclusions:  Elevated Hcy levels seem to be associated with cognitive impairment in euthymic bipolar patients, but not with psychosocial functioning. More studies are needed to clarify the role of Hcy in cognition in bipolar disorder.