2.3. Eligibility Criteria

Two authors independently reviewed the retrieved articles for eligibility according to the following inclusion criteria: 1) studies on the association between the COMT Val158Met polymorphism and antipsychotic response; 2) patients diagnosed with schizophrenia according to DSM-III, DSM-IV, DSM-5, or ICD-10 criteria and verified through a standardized structured clinical interview; 3) antipsychotic response estimated based on a standardized clinical rating scale, such as the Brief Psychiatric Rating Scale (BPRS) or the Positive and Negative Syndrome Scale (PANSS). Studies focused on intermediate phenotypes such as cognitive response or structural brain alterations were excluded. Authors of studies meeting inclusion criteria, but without effect sizes were contacted for this data. A total of 30 independent investigations with 6291 study subjects met inclusion criteria.

To investigate whether ethnicity can affect the association between the COMT Val158Met polymorphism and antipsychotic treatment efficacy, separate subgroup analyses were conducted in Caucasian and Asian populations.