Diagnostic classification of psychiatric disorders and familial-genetic research.

The validity of diagnostic definitions in psychiatry is directly related to the extent to which their etiology can be specified. However, since detailed knowledge of causal or susceptibility factors is lacking for most psychiatric disorders with a known or suspected familial-genetic origin, the current widely accepted classification systems largely fail to achieve this ideal. To illustrate this problem, this paper looks at the difficulties posed by the criteria for schizophrenia as laid down in the International Classification of Diseases, 10th revision (ICD-10) and the Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised (DSM-III-R), and highlights the discrepancies between the majority of diagnostic boundaries and the various phenotype aggregation patterns observed in family studies. Progress in our understanding of psychiatric disorders requires to be firmly based on the findings of epidemiological studies as well as on a clear appreciation of the limitations of classification tools.