Phenotypic variation between parent-offspring trios and non-trios in genetic studies of schizophrenia.

Background: Phenotypic differences between parent-offspring trios and non-trios have been reported for various psychiatric disorders, and it has been suggested that this may make comparisons of case-control and family-based results for gene-disease association studies inappropriate.

Aims: To compare phenotypes between trios and non-trios with schizophrenia, and explore possible reasons for differences observed.

Method: Phenotypes were compared between trios (n=75) and non-trios (n=424) collected as part of a case-control study.

Results: Differences were observed for most phenotypes investigated, although all were eliminated after adjusting for confounding.

Conclusions: Confounding, genetic heterogeneity or selection bias could result in differences in case-control and family-based results. However as we discuss, where adequately designed case-control studies are used, gene-disease association results would be incomparable between family-based and case-control studies only if genetic heterogeneity was present. These results do not support the presence of such genetic heterogeneity in schizophrenia.