Conceptualization of vulnerability models for schizophrenia: historical aspects

The conceptualization of vulnerability started around the middle of the 19th century with the emergence of the theories of degeneration that attributed mental disorders to a hereditarily transmitted predisposition reducing the individual psychological resistance. This condition was considered to be the basis of all "endogenous psychoses" whose different types were considered to be caused by additional pathoplastic influences. During the first half of the 20th century the idea of degeneration was abandoned and affective and schizophrenic disorders were conceived as different genetically caused diseases. Further research indicated that the propensity to develop a schizophrenic disorder may sometimes be caused by acquired etiological factors. In both cases it has been observed that this predisposition manifests itself as an overt illness only under the impact of environmental stress. This enhanced attempts to investigate more precisely the different factors implicated in the genesis of the "vulnerability" for schizophrenia and to determine more precisely the conditions that precipitate the clinical manifestation of disorders diagnosed as schizophrenic. In this perspective several vulnerability models for schizophrenia as well as for its subsyndromes have been proposed. Despite these efforts, the question whether schizophrenic disorders are caused by a specific predisposition or are only dimensions of an "unitary psychosis" has not yet been definitively resolved.