title: Cognitive heterogeneity in schizophrenia.
abstract: OBJECTIVE
  Further clarification of the nature of cognitive heterogeneity in schizophrenia is needed to aid the endophenotype approach to the understanding of the genetic basis of the disorder. This review summarizes recent neuropsychological studies of schizophrenia, aimed at establishing whether there are valid forms of cognitive impairment that can be defined with the use of neuropsychological measures in patients with schizophrenia, and studies that have attempted to relate specific neuropsychological findings to genetic polymorphisms.
  
  
  RESULTS
  There is good evidence for significant cognitive heterogeneity in schizophrenia. It is not yet clear, however, whether this heterogeneity is better accounted for by a general loss of function, varying in degree between different patients, or by impairment in specific cognitive abilities, for example working memory. Molecular genetic studies have provided evidence for associations of single nucleotide polymorphisms with both specific and general impairments, with some additional support for a working memory deficit from neuroimaging studies.
  
  
  CONCLUSIONS
  Larger, better controlled studies are needed before the genetic sources of cognitive heterogeneity in schizophrenia can be accurately characterized. This will be aided with the development and use of more specific neuropsychological tasks that can accurately discriminate between different cognitive domains.
authors.affiliation: UCL Institute of Neurology, London, UK. e.joyce@ion.ucl.ac.uk
authors.forename: Eileen M
authors.initials: EM
authors.lastname: Joyce
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Roiser
mesh_terms: D002352:Carrier Proteins / Q000235:genetics; D002394:Catechol O-Methyltransferase / Q000235:genetics; D003072:Cognition Disorders / Q000175:diagnosis* / Q000235:genetics / Q000523:psychology; D004292:Dominance, Cerebral / Q000502:physiology; D000074765:Dysbindin; D049029:Dystrophin-Associated Proteins; D006801:Humans; D007360:Intelligence / Q000235:genetics; D008279:Magnetic Resonance Imaging; D008570:Memory, Short-Term; D009483:Neuropsychological Tests; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D017397:Prefrontal Cortex / Q000473:pathology; D012559:Schizophrenia / Q000175:diagnosis* / Q000235:genetics; D012565:Schizophrenic Psychology
chemical_list: D002352:Carrier Proteins; C432416:DTNBP1 protein, human; D000074765:Dysbindin; D049029:Dystrophin-Associated Proteins; D002394:Catechol O-Methyltransferase