title: Genes for schizophrenia and bipolar disorder? Implications for psychiatric nosology.
abstract: 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 continuing to rely heavily on the traditional Kraepelinian dichotomy. As psychosis susceptibility genes are identified and characterized over the next few years, this will have a major impact on our understanding of disease pathophysiology and will lead to changes in classification and the clinical practice of psychiatry.
authors.affiliation: Department of Psychological Medicine, Henry Wellcome Building, Wales School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, UK. craddockn@cardiff.ac.uk
authors.forename: Nick
authors.initials: N
authors.lastname: Craddock
authors.forename: Michael C
authors.initials: MC
authors.lastname: O'Donovan
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Owen
mesh_terms: D001714:Bipolar Disorder / Q000235:genetics*; D019208:Brain-Derived Neurotrophic Factor / Q000235:genetics*; D002352:Carrier Proteins / Q000235:genetics*; D002394:Catechol O-Methyltransferase / Q000235:genetics*; D000074765:Dysbindin; D049029:Dystrophin-Associated Proteins; D008040:Genetic Linkage / Q000235:genetics; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D009419:Nerve Tissue Proteins / Q000235:genetics*; D020890:Neuregulin-1; D012559:Schizophrenia / Q000235:genetics*
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D002352:Carrier Proteins; C475071:DAOA protein, human; C412476:DISC1 protein, human; C432416:DTNBP1 protein, human; D000074765:Dysbindin; D049029:Dystrophin-Associated Proteins; D047908:Intracellular Signaling Peptides and Proteins; C094131:NRG1 protein, human; D009419:Nerve Tissue Proteins; D020890:Neuregulin-1; D002394:Catechol O-Methyltransferase