The enigmatic phenotype: Relevant signs and symptoms in schizophrenia

Ever since schizophrenia was conceptualized by Kraepelin and Bleuler, attempts have been made to rearrange signs and symptoms in order to achieve an useful disease concept with consequences for outcome, prognosis, treatment response and etiology. Several procedures were used to describe relevant phenotypes of the disease. In the beginning, famous psychiatrists conceptualized definitions of schizophrenia which was followed by a consensus about the operational criteria of schizophrenia. Later, more emphasis was placed on the statistical analyses of symptoms present in patients with psychotic disorders which resulted in a great variety of symptom clusters. In another approach, investigators try to deconstruct psychiatric diagnoses in search for so called endophenotypes of which covert symptoms like cognitive deficits in schizophrenia, are an example. The value of all these endeavours ultimately depends on the external validity which means that a relationship has to be established with the etiology, treatment response and outcome. The premises of all these research efforts is, however, the idea that the pathogenic agent of schizophrenia or a subtype will be found. In this paper an outline of the literature about the ordening of overt and covert symptoms in schizophrenia is presented. It is concluded that the different approaches are essential analogue and that research into the delineation of cognitive deficits and their treatment is at present most promising.