Extending the phenotype of schizophrenia: implications for linkage analysis.

On the basis of simulation studies, we suggest that most existing designs for studying linkage in schizophrenia do not have sufficient power to detect a major contributing locus, even if one is present. For this reason, recent failures to replicate reports of linkage in schizophrenia are not surprising. Inclusion in the linkage design of phenotypes genetically related to schizophrenia, but more commonly found in the relatives of schizophrenics than schizophrenia itself, may increase the power of linkage analysis substantially.