The present invention provides methods for treating or ameliorating the effects of schizophrenia, which include administering to a patient in need thereof a therapeutically effective amount of a proline modulator. Further provided are methods of selecting a patient at risk for or suffering from schizophrenia that is likely to benefit from proline modulation. Methods for identifying an agent that modulates proline levels in a patient and methods for identifying a patient at risk for developing a DTNBP1-related psychiatric illness, as well as other methods and compositions for treating or ameliorating the effects of schizophrenia are also provided.
