D-serine serum levels in patients with schizophrenia: relation to psychopathology and comparison to healthy subjects.

OBJECTIVES: The main objective was to test the hypothesis of the association between D-serine serum levels and negative symptoms in patients with schizophrenia. Secondary objective was to examine the assumption of D-serine serum levels difference between a population of mostly chronic patients with schizophrenia and healthy controls.

METHODS: We recruited outpatients with schizophrenia and age and gender matched healthy controls for the study. D-serine and total serine serum levels were measured by high-performance liquid chromatography (HPLC). The Positive and Negative Syndrome Scale (PANSS) and The Scale for the Assessment of Negative Symptoms (SANS) were used to assess schizophrenic symptoms. Non-parametric statistics was used to test the differences in D-serine and total serine serum levels and rank correlation was used to detect the associations with psychopathology.

RESULTS: We did not find any differences between patients (n=50) and controls (n=50) in D-serine serum levels. Patients had significantly lower total serine serum levels and higher D-serine/total serine ratio. D-serine serum levels were not associated with the PANSS or the SANS total and subscales scores. Total se-rine serum levels inversely correlated with the SANS total and the PANSS negative symptom subscale scores.

CONCLUSION: Decreased, not increased, serum levels of total serine negatively associated with intensity of negative symptoms were detected in patients with schizophrenia. We did not find any relationship between D-serine serum levels and negative symptoms among the patients. These findings do not agree with the previous reports of decreased D-serine and increased total serine serum levels in schizophrenia.