The etiology of schizophrenia remains unclear. In recent one decade, hypofunction of N-methyl-D-aspartate (NMDA) receptor has been implicated in the pathophysiology of schizophrenia. Hence, enhancing NMDA neurotransmission was considered as a new approach for schizophrenia treatment. To date, there have been a few pilot studies exploring the efficacy of NMDA enhancers as adjuvant therapy for schizophrenia, for instance, D-serine (an endogenous agonist of the NMDA-glycine site). They were not only well-tolerated but also synergistic in improving positive, negative and cognitive symptoms in those receiving typical and atypical antipsychotics (except clozapine).
Refractory schizophrenia (particularly clozapine-resistant) is still a difficult clinical issue at present. Previous studies revealed that add-on treatment of D-serine or other agonists of NMDA receptor failed to give significant benefits in such patients. The primary goal of this study is to investigate the efficacy and safety of glycine transporter(GlyT)-1 inhibitor adjuvant therapy in refractory schizophrenia, and to identify the predictors for treatment response to NMDA enhancers.
