GRM2 and schizophrenia: However, antipsychotic efficacy of mGlu2/3 agonists or mGlu2 receptor PAMs may be restricted to those subjects with schizophrenia not previously exposed to atypical antipsychotics with nearly complete 5-HT2A receptor blockade or in those subjects early in their personal trajectory with schizophrenia (Patil et al., 2007; Kinon et al., 2015).