Molecular Genetics and the Kraepelinian Dichotomy: One Disorder, Two Disorders, or Do We Need to Start Thinking Afresh?

By Nick Craddock, MA, MD, MmedSci, PhD, FRCPsych; Michael J. Owen

The Kraepelinian dichotomy — the broad division of the major mood and psychotic illnesses of adulthood into schizophrenia and manic depressive illness — has been enshrined in Western psychiatry for more than a century and continues to influence clinical practice, research, and public perceptions of mental illness. Although cogent arguments for abandoning an essentially dichotomous approach in favor of alternative formulations (categorical, dimensional, or continuous) have often been advanced, these have failed to gain widespread support, in part because of lack of robust scientific data, but possibly also because of the practical complexity of applying alternative classifications in clinical practice and research settings.

ABOUT THE AUTHORS

Nick Craddock, MA, MMedSci, PhD, FRCPsych; and Prof. Michael J. Owen are with Medical Research Council (MRC) Centre for Neuropsychiatric Genetics and Genomics, School of Medicine, Cardiff University, Heath Park, Cardiff, United Kingdom.

Address correspondence to: Nick Craddock, MRC Centre for Neuropsychiatric Genetics and Genomics, Henry Wellcome Building, School of Medicine, Cardiff University, Heath Park, Cardiff, CF14 4XN, UK; or e-mail: craddockn@cardiff.ac.uk.

The authors’ work on the genetics of psychosis and mood disorders is funded through grants from the Wellcome Trust, MRC, National Institutes of Health (NIH), and Stanley Medical Research Institute. Prof. Craddock and Prof. Owen have disclosed no relevant financial relationships.

Prof. Owen is a member of the Diagnostic and Statistical Manual of Mental Disorders, fifth edition, (DSM-V) Work Group on Psychotic Disorders. The opinions expressed in this article do not necessarily reflect the consensus of the DSM-V Work Group or Task Force.

The authors wish to thank all participants in their studies.

doi: 10.3928/00485718-20100127-04

EDUCATIONAL OBJECTIVES

1. Cite genetic findings in mood and psychotic illness.

2. Review implications of recent genetic findings for understanding the relationship between mood and psychotic illness.

3. Discuss implications of recent findings for understanding the relationship between mood and psychotic illness and other psychiatric phenotypes, such as autism.

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