Decreased plasma levels of neureglin-1 in drug naïve patients and chronic patients with schizophrenia

Although the neuregulin-1 (NRG1) gene is one of the susceptibility genes for schizophrenia and various other psychiatric diseases, it remains unclear how individual psychiatric diseases affect the expression of the NRG1 protein in patients. A previous study reported a schizophrenia-linked decrease in serum NRG1 levels. The present study aimed to replicate this initial finding and to assess its disease specificity for schizophrenia. We collected plasma samples from drug-naïve patients with first-episode schizophrenia (n=80), patients with chronic schizophrenia (n=86), patients with bipolar I disorder (n=60), patients with bipolar II disorder (n=60) and patients with major depressive disorder (n=60), we measured the plasma levels of NRG1β1 and compared the levels with those of age- and sex-matched healthy volunteers (n=82). One-way ANOVA and post hoc analyses detected specific NRG1β1 decreases in the participants with first-episode and chronic schizophrenia but not in those with bipolar I disorder, bipolar II disorder or major depressive disorder. The mean plasma levels of NRG1β1 immunoreactivity were 4.27±0.71 ng/mL in the participants with first-episode schizophrenia, 4.08±0.64 ng/mL in the participants with chronic schizophrenia and 7.21±0.91 ng/mL in the healthy controls. Although we analyzed the pathological correlations of NRG1β1 immunoreactivity in terms of the clinical parameters of the sample, we observed only weak positive correlations with the age of the participants with chronic schizophrenia and the disease onset times of the participants with bipolar II disorder. We failed to identify correlations between other clinical parameters and plasma NRG1β1 immunoreactivity among all patient subjects. These findings suggest that NRG1 may serve as a relatively specific disease marker for schizophrenia. However, the pathological role of this decrease must be explored further.