Schizotypal disorder: at the crossroads of genetics and nosology.

The aim of this paper is to review the available evidence in support of the correctness of including the DSM-III/III-R schizotypal personality disorder (SPD) in the schizophrenia spectrum, to discuss the components that may account for the familial segregation of SPD, and to consider the implications for research and clinical use of this diagnostic category. The majority of the available data from genetic epidemiology studies, starting from probands with schizophrenia or with SPD, suggest that SPD is one of several phenotypes of liability for the schizophrenia spectrum. Recent twin studies suggest that the affect-constricted and eccentric aspects of SPD are the features that truly belong to the spectrum of schizophrenia, sharing important genetic influences. However, other components are more useful for the identification of SPD in clinical settings, and these may be the specific focus of treatment. The present categorization appears to be a reasonable trade-off for the purposes of both the investigator and the clinician, even though different components within SPD may have different origins and can be selectively emphasized according to the different aims involved.