Clinical phenotype of schizophrenia in a Finnish isolate

We identified all cases in Finland (population of 5 million) with a diagnosis of schizophrenia born between 1940 and 1969, using four national computerised registers with high reliability. A sample of 397 families was identified in a genetically homogeneous internal isolate (population of 18,000) in northeastern Finland with high prevalence for schizophrenia and an LOD score of 3.8 in chromosome 1. Our aim was to examine with Operational Criteria Checklist for Psychotic Illness (OCCPI) factor analysis the psychotic and affective signs and symptoms of schizophrenia in this genetically homogeneous population, and compare them with findings from individuals with schizophrenia from multiplex families from the whole country. After collecting all original case notes, we made DSM-IV consensus diagnoses and completed OCCPI ratings on a lifetime basis. For the factor analysis, we accepted 190 patients with a diagnosis of schizophrenia. In addition, 466 schizophrenia patients from 147 multiplex families from the whole country were included in the analysis. The OCCPI factor analysis resulted in four factors: "delusions and hallucinations" and "negative" factors, plus two affective ("manic" and "depressive") factors. We compared the pattern of symptoms among three patient groups: isolate patients who were the only affected individuals in their family, isolate patients who had affected family members, and patients from the whole country with affected family members. We found no clear differences among these groups. However, there were significant differences in the frequency of individual OCCPI items between the study groups. Findings in this schizophrenia OCCPI phenotype study suggest that the clinical picture of schizophrenia in a genetically isolated and homogeneous population closely resembles our nationwide findings in Finland.