Like many other researchers and clinicians, Nick Craddock and Mike Owen of Cardiff University in Wales feel that the traditional boundaries of psychotic and mood disorders may be getting in the way of progress in basic research, particularly genetics. In the past year, they have published a series of papers, both theoretical and experimental, that argue for moving beyond the Kraepelinian dichotomy of schizophrenia and bipolar disorder as distinct disease entities.
On May 15, 2006, Craddock and Owen led us through a live online discussion of these issues, with an eye toward finding alternative approaches to diagnosis and classification. Mayada Akil of the National Institute of Mental Health served as moderator. Please read the edited transcript, two recent review papers (full text can be accessed by clicking on the journal images above), and the text below and continue this discussion by offering comments.
by Nick Craddock and Mike Owen
It has been conventional for psychiatric research, including the search for predisposing genes, to proceed under the assumption that schizophrenia and bipolar disorder are separate disease entities with different underlying etiologies. These represent Emil Kraepelin's traditional dichotomous classification of the so-called "functional" psychoses and form the basis of modern diagnostic practice. However, findings emerging from many fields of psychiatric research do not fit well with this model. In particular, the pattern of findings emerging from genetic studies shows increasing evidence for an overlap in genetic susceptibility across the traditional classification categories, including association findings at DAOA(G72), DTNBP1 (dysbindin), COMT, BDNF, DISC1, and NRG1. The emerging evidence suggests the possibility of relatively specific relationships between genotype and psychopathology. For example, DISC1 and NRG1 may confer susceptibility to a form of illness with mixed features of schizophrenia and mania. The elucidation of genotype-phenotype relationships is at an early stage, but current findings highlight the need to consider alternative approaches to classification and conceptualization for psychiatric research rather than continue to rely heavily on the traditional Kraepelinian dichotomy.
The aim of this Schizophrenia Research Forum discussion is to discuss the current utility, or otherwise, of the Kraepelinian dichotomy for research and clinical practice and consider this against alternative approaches to diagnosis and classification. To focus discussion, two specific issues will be addressed, in the form of questions:
1) Do the disadvantages of the Kraepelinian dichotomy now outweigh the advantages?
2) What are the best alternative approaches to diagnosis and classification? (e.g., dimensions, alternative categories, prototypes.")
References: Craddock N, O'Donovan MC, Owen MJ. Genes for schizophrenia and bipolar disorder? Implications for psychiatricnosology. Schizophr Bull. 2006 Jan;32(1):9-16. Abstract
Craddock N, Owen MJ. The beginning of the end for the Kraepelinian dichotomy. Br J Psychiatry. 2005 May;186:364-6. Abstract