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The biopsychosocial model of mental disorders posits that the interactions of biological, psychological, and social risk factors best account for the development of mental disorders (Engel 1980). This model seems applicable to the personality disorders, which have a complex and multidimensional etiology (Tyrer 1988).
Etiological theories in psychiatry also need to account for the specificity of psychopathology, that is, why different individuals develop different disorders. The dominant paradigm in contemporary psychiatry, neo-Kraepelinian theory (Klerman 1986), can be considered as a variant of the biopsychosocial model in which biological vulnerability explains the specificity of psychopathology (Cloninger 1990). Neo-Kraepelinian theory is essentially identical to predisposition-stress models that have been applied to the major functional psychoses (Gottesman 1991).
Predisposition-stress models contrast with those psychological theories that invoke specific developmental experiences to account for specific disorders. The problem with such formulations is that many negative events in childhood are highly prevalent in patients who have entirely different disorders and can also be found in individuals with no mental disorder (Rutter 1989). In the neo-Kraepelinian model, psychological or social factors are seen as nonspecific stressors that precipitate a transition from predisposition to overt psychopathology. The model therefore predicts that each psychiatric disorder should be validated by the presence of biological markers that reflect a specific vulnerability (Robins and Barrett 1982). Although this paradigm has been widely used for DSM Axis I conditions, its application to the etiology of the personality disorders is more recent (Siever and Davis 1991).
The biological factors in the personality disorders may be reflected in underlying temperamental factors. Temperament is a major influence on the development of personality traits (Rutter 1989). These traits are patterns of affect, cognition, and behavior that are consistent in a variety of interpersonal contexts. There is evidence that personality traits, as measured by self-report questionnaires, are under strong genetic influence (Plomin et al. 1990; Tellegen et al. 1988). There is also evidence that personality traits and disorders lie on a continuum (Livesley et al. 19921.
Variability in personality traits is entirely compatible with normality. Only additional risk factors would amplify traits to the point that they become maladaptive, and would therefore justify a diagnosis of personality disorder (Paris in press). These additional risk factors could be biological, in that certain traits...