Estimating the genetic contribution to schizophrenia.

The authors discuss the limitations of the concept of heritability in schizophrenia and, using reported incidence figures, assess two alternatives--the multifactorial and single major locus (SML) models. Both models predict genetic heterogeneity in schizophrenia. For some parameter values, the SML model indicates that homozygotes are rare but at very high risk. According to the multifactorial model, 9.1% of the schizophrenic population has a genetic risk of 99% or more. The authors conclude that neither model adequately accounts for the data but that predictions from both can be used to design sampling procedures which will increase the probability of selecting for study individuals whose illness is highly genetically determined.