Genetic link between schizophrenia and cognitive impairment
30 September 2010
New research from the Institute of Psychiatry (IoP) at King’s College London points to a genetic link between schizophrenia and cognitive impairment. These findings have the potential to help identify the genes causing schizophrenia, and could pave the way for earlier diagnosis and individualised treatment.
Patients with schizophrenia are known to have abnormalities in cognitive functions, such as intellect and memory. It has been speculated that impaired cognition could represent an intermediate state between genetic risk for schizophrenia and the disorder itself, known as an endophenotype. Identifying endophenotypes genetically linked to schizophrenia would help researchers to better understand the pathogenesis of the disorder.
To determine the extent of genetic overlap between schizophrenia and cognitive impairment (specifically, intelligence, immediate recall and delayed recall), Dr Timothea Toulopoulou and colleagues combined family and twin data to create the largest international database of cognitive function in schizophrenia.
Using genetic modelling, they showed that genes, and not environmental factors, were responsible for a substantial portion of the correlation between schizophrenia and cognitive impairment. The results suggested that 89% of the correlation between schizophrenia and intelligence, 72% of the correlation between schizophrenia and immediate recall, and 86% of the correlation between schizophrenia and delayed recall was due to genetic factors.
These findings suggest that schizophrenia and cognition share, to some extent, the same genes, thus validating intelligence, immediate recall and delayed recall as endophenotypes for schizophrenia. However, the study also found that over half the schizophrenia risk genes did not affect cognition, suggesting that there is more to the genetics of schizophrenia than simply the genetic determinants of cognitive impairment.
Psychiatric classification currently depends almost entirely on clinical symptoms, leading to inconsistencies in molecular genetic studies. According to the researchers, grouping schizophrenia patients according to cognitive performance could potentially help to identify the schizophrenia risk genes.
Dr Timothea Toulopoulou, who led the study said: 'his is one of the first steps in helping us to see that the clinical diagnosis of schizophrenia, long conceptualised as a syndrome, may be dissectible into constituent parts, each more intimately connected to the pathophysiology and the aetiology of the disorder.'
The paper is published in the Archives of General Psychiatry: Toulopoulou, T. et al. , Impaired intellect and memory: a missing link between genetic risk and schizophrenia?, Vol. 67 No. 9, pp 905-13. September 2010.