Twin studies in schizophrenia with special emphasis on concordance figures

Twin studies in schizophrenia have been reviewed with special emphasis on concordance rates in population-based investigations. Sources of error have been discussed with particular focus on sampling. The pair-wise concordance rates in schizophrenia are 30-40% in MZ and 5-10% in DZ, with somewhat higher rates for proband concordance. The findings from twin studies support the diathesis stress model in schizophrenia, and it is argued that the polygenic model gives the best explanation for the empirical findings.