Testing Liddle's three-syndrome model in families with schizophrenia

While the symptoms of schizophrenia can be grouped into positive and negative syndromes, increasing evidence suggests that three clusters of symptoms are present. Liddle (1987a) described a three-syndrome model comprised of reality distortion, psychomotor poverty and disorganization symptom clusters. This model was assessed in the present study using a sample of 72 members of five families segregating schizophrenia. A wide range of psychopathology was present across a spectrum of diagnoses. Data on symptoms used in Liddle's model were derived from the Positive and Negative Syndrome Scale (PANSS) and a mental status examination. Factor analysis of the data indicated the presence of three clusters of symptoms. The psychomotor poverty or negative symptom cluster was confirmed in the familial sample. However, the other two factors differed somewhat from the Liddle model. Hallucinations, delusions, disorganized thinking and inappropriate affect formed one factor; suspiciousness and stereotyped thinking formed the other. These three symptom clusters may be comparable to the catatonic, hebephrenic and paranoid classical subtypes of schizophrenia. The implications of Liddle's model for genetic studies of schizophrenia require further investigation.