Subjects

In total, 153 Chinese Han subjects were recruited for the current study, including 33 patients with schizophrenia (SZ), 61 of their unaffected biological parents (PA) (30 fathers and 31 mothers), 30 young healthy controls for the patients (HC1) and 29 old healthy controls for the unaffected parents (HC2).

The SZ and PA groups were recruited from the Peking University Sixth Hospital. The diagnosis of schizophrenia was made according to ICD-10 diagnostic criteria for paranoid schizophrenia by at least two trained and skilled psychiatrists. All patients were under antipsychotic medication when they were enrolled in the study, and the dosages were converted to the equivalent dose of chlorpromazine. More than half of the patients were under combination medication. The Positive and Negative Syndrome Scale (PANSS)²⁸ was used to assess the severity of disease. Patients who had a history of serious medical illness or those who were treated with electroconvulsive therapy during the previous 6 months were excluded from the study. The HC1 and HC2 groups were recruited from the local community. They were well matched with the patients and parents group with regard to age, gender and education level. The exclusion criteria for the healthy controls included having any first- or second-degree relatives with schizophrenia spectrum disorders, intracranial pathology, history of brain injury, neurological disorders and alcohol/substance abuse. All first-degree relatives and normal controls were interviewed by a psychiatrist in order to exclude a previous or current diagnosis of any mental illnesses. The right-handedness of all participants was assessed using the Edinburgh Handedness Inventory.²⁹

The study was approved by the Medical Ethics Committee of Peking University Sixth Hospital. Prior to written consent being obtained, the research objective and procedures were explained in detail to all participants. All available biological parents of the patients were invited to participate in this study, and therefore written consent was given by the patients and their parents, as well as all healthy participants enrolled in this study. This study was conducted in accordance with the Declaration of Helsinki.