HTR2A and psychotic disorder: For example, HTR2A encodes the 5-hydroxytryptamine 2A receptor, a major postsynaptic target for serotonin in the human brain that has been functionally linked to psychosis and antipsychotic response.37 In the module that is significantly correlated with the 5-HIAA:MHPG ratio, the hub genes GSK3B and TCF4 seem particularly relevant to neuropsychiatric disease.