SCHIZOPHRENIA IN THE GENETIC ISOLATE OF FINLAND

We compared the features of schizophrenia in the homogeneous populatio n of Finland (population about 5,000,000) and in an internal isolate i n northeastern Finland inhabited in the 1680s by a small group of foun ders (current population about 18,000) in a register-based epidemiolog ical study. We identified all cases with a diagnosis of schizophrenia in Finland born between 1940-1969 using three national computerized re gisters and found a total of 267 schizophrenia patients in the interna l isolate and 29,124 in Finland. The lifetime prevalence was 2.21% in the internal isolate and 1.21% in Finland, respectively. The age-corre cted lifetime risk was 3.2% in the internal isolate and 1.1% in the wh ole country. The risk of schizophrenia to siblings in the internal iso late was 6.4% (95% confidence interval 0.052, 0.078), 9.1% (95% CI 0.0 62, 0.130), and 6.8% (95% CI 0.028, 0.135) given 1, 2, or 3 affected s iblings, and for all Finland 4.2% (95% CI 0.036, 0.043), 6.4% (95% CI 0.058, 0.071), and 8.7% (95% CI 0.068, 0.107) given 1, 2, or 3, affect ed siblings, respectively. The mean number of children in schizophreni a families and thus the number of families having at least two affecte d individuals were clearly higher in the isolate (24.9% vs 9.2%). We d id not find any other epidemiological features differing between these two regions. It seems that the family material collected from the int ernal isolate is a representative subsample from the entire country an d hopefully it enables easier identification of at least some predispo sing genes for schizophrenia due to its unique population structure. ( C) 1997 Wiley-Liss, Inc.